Introduction Acknowledgements 1 Installing MDK 1.1 Download the source tarball 1.2 Requirements 1.3 Basic installation 1.4 Emacs support 1.5 Special configure flags 1.6 Supported platforms 2 MIX and MIXAL tutorial 2.1 The MIX computer 2.2 MIXAL 3 Getting started 3.1 Writing a source file 3.2 Compiling 3.3 Running the program 3.4 Using 'mixguile' 3.5 Using Scheme in 'mixvm' and 'gmixvm' 4 Emacs tools 4.1 MIXAL mode 4.2 GUD integration 5 'mixasm', the MIXAL assembler 5.1 Invoking 'mixasm' 6 'mixvm', the MIX computer simulator 6.1 Invoking 'mixvm' 6.2 Interactive commands 6.3 MIX block devices 7 'gmixvm', the GTK virtual machine 7.1 Invoking 'gmixvm' 7.2 MIXVM console 7.3 MIX virtual machine 7.4 MIXAL source view 7.5 MIX devices view 7.6 Menu and status bars 8 'mixguile', the Scheme virtual machine 8.1 Invoking 'mixguile' 8.2 Scheme functions reference 9 Reporting Bugs Appendix A Copying A.1 GNU General Public License A.2 GNU Free Documentation License Concept Index Instructions and commands Introduction Acknowledgements 1 Installing MDK 1.1 Download the source tarball 1.2 Requirements 1.3 Basic installation 1.4 Emacs support 1.5 Special configure flags 1.6 Supported platforms 2 MIX and MIXAL tutorial 2.1 The MIX computer 2.1.1 MIX architecture 2.1.2 MIX instruction set 2.1.2.1 Instruction structure 2.1.2.2 Loading operators 2.1.2.3 Storing operators 2.1.2.4 Arithmetic operators 2.1.2.5 Address transfer operators 2.1.2.6 Comparison operators 2.1.2.7 Jump operators 2.1.2.8 Input-output operators 2.1.2.9 Conversion operators 2.1.2.10 Shift operators 2.1.2.11 Miscellaneous operators 2.1.2.12 Execution times 2.2 MIXAL 2.2.1 Basic program structure 2.2.2 MIXAL directives 2.2.3 Expressions 2.2.4 W-expressions 2.2.5 Local symbols 2.2.6 Literal constants 3 Getting started 3.1 Writing a source file 3.2 Compiling 3.3 Running the program 3.3.1 Non-interactive mode 3.3.2 Interactive mode 3.3.3 Debugging commands 3.4 Using 'mixguile' 3.4.1 The 'mixguile' shell 3.4.2 Additional MIX Scheme functions 3.4.3 Defining new functions 3.4.4 Hook functions 3.4.4.1 Command hooks 3.4.4.2 Break hooks 3.4.5 Scheme scripts 3.5 Using Scheme in 'mixvm' and 'gmixvm' 4 Emacs tools 4.1 MIXAL mode 4.1.1 Basics 4.1.2 Help system 4.1.3 Compiling and running 4.2 GUD integration 5 'mixasm', the MIXAL assembler 5.1 Invoking 'mixasm' 6 'mixvm', the MIX computer simulator 6.1 Invoking 'mixvm' 6.2 Interactive commands 6.2.1 File commands 6.2.2 Debug commands 6.2.3 State commands 6.2.4 Configuration commands 6.2.5 Scheme commands 6.3 MIX block devices 7 'gmixvm', the GTK virtual machine 7.1 Invoking 'gmixvm' 7.2 MIXVM console 7.3 MIX virtual machine 7.4 MIXAL source view 7.5 MIX devices view 7.6 Menu and status bars 8 'mixguile', the Scheme virtual machine 8.1 Invoking 'mixguile' 8.2 Scheme functions reference 8.2.1 'mixvm' command wrappers 8.2.2 Hook functions 8.2.3 Additional VM functions 9 Reporting Bugs Appendix A Copying A.1 GNU General Public License A.2 GNU Free Documentation License Concept Index Instructions and commands This manual is for GNU MDK (version 1.3.0, October, 2020), a set of utilities for developing programs using Donald Knuth's MIX mythical computer and MIXAL, its assembly language. Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2008, 2009, 2010, 2013, 2014, 2015, 2020 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with the Invariant Sections being "GNU General Public License", with the Front-Cover Texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom." GNU MDK was written and designed by Jose Antonio Ortega Ruiz. Pieter E. J. Pareit is the author of the Emacs 'MIXAL' mode (*note MIXAL mode::), and has also contributed many bug fixes. Philip E. King has contributed to this package development with many helpful discussions, as well as actual code (*note GUD integration::). Michael Scholz is the author of the German translation of MDK's user interface. Introduction ************ In his book series 'The Art of Computer Programming' (published by Addison Wesley), D. Knuth uses an imaginary computer, the MIX, and its associated machine-code and assembly languages to illustrate the concepts and algorithms as they are presented. The MIX's architecture is a simplified version of those found in real CISC CPUs, and the MIX assembly language (MIXAL) provides a set of primitives that will be very familiar to any person with a minimum experience in assembly programming. The MIX/MIXAL definition is powerful and complete enough to provide a virtual development platform for writing quite complex programs, and close enough to real computers to be worth using when learning programming techniques. At any rate, if you want to learn or improve your programming skills, a MIX development environment would come in handy. The MDK package aims at providing such virtual development environment on a GNU box. Thus, MDK offers you a set of utilities to simulate the MIX computer and to write, compile, run and debug MIXAL programs. As of version 1.3.0, MDK includes the following programs: 'mixasm' MIXAL assembler. Assembler which translates MIXAL source files into programs that can be run (and debugged) by 'mixvm', 'mixguile' or 'gmixvm'. 'mixvm' MIX virtual machine. Emulation of the MIX computer with a CLI. 'gmixvm' A GTK+ GUI for the MIX virtual machine. Provides all of 'mixvm' functionality accessible through a graphical interface. 'mixguile' A Guile shell, with an embedded MIX virtual machine and built-in commands to manipulate it using Scheme. 'mixal-mode.el' An Emacs major mode for MIXAL source files editing, providing syntax highlighting, documentation lookup and invocation of 'mixvm' within Emacs. 'mixvm.el' This elisp program allows running 'mixvm' inside an Emacs GUD buffer, providing concurrent edition and debugging of MIXAL programs. 'mixvm' and 'gmixvm' implement a simulator of the MIX computer, giving you a virtual machine for executing and debugging MIX programs. These binary programs could be written by hand, but it is easier to produce them compiling MIXAL source files, using the MIXAL assembler 'mixasm'. On the other hand, 'mixguile' offers you the possibility of manipulating a MIX virtual machine through a set of Scheme functions, so that you can use this programming language to interact with the virtual machine. In addition, 'mixvm' and 'gmixvm' are also able to interpret Scheme scripts (using an embedded Guile interpreter), that is, you can use Scheme as an extension language to add new functionalities to these programs. This manual gives you a tutorial of MIX and MIXAL, and a thorough description of the use of the MDK utilities. Acknowledgements **************** Many people have further contributed to MDK by reporting problems, suggesting various improvements, or submitting actual code. Here is a list of these people. Please, help me keep it complete and exempt of errors. * Philip Ellis King provided MIXAL test programs pinpointing bugs in the first MDK release, and useful discussions as well. Philip has also contributed with the Emacs port of 'mixvm' and influenced the 'gmixvm' GUI design with insightful comments and prototypes. * Aleix Conchillo has been following MDK's development for many years, indefatigably chasing and fixing bugs, and suggesting many improvements. He's also the original author of the Fink and Macports ports. * Pieter E J Pareit is the author of the Emacs MIXAL mode, and has also contributed many bug fixes. * Michael Scholz is the author of the German translation of MDK's user interface. * Sergey Poznyakoff provided patches to mixlib/mix_scanner.l improving MIXAL compliance. * Sergey Litvin implemented the instructions 'SLB', 'SRB', 'JAE', 'JAO', 'JXE', and 'JXO' from volume 2 of TAOCP. * Francesc Xavier Noria kindly and thoroughly reviewed the MDK documentation, providing insightful advice. * Eric S. Raymond contributed the documentation file 'MIX.DOC' and the samples 'elevator.mixal' and 'mistery.mixal' from his MIXAL package. * Nelson H. F. Beebe has tested MDK in a lot of Unix platforms, suggesting portability enhancements to the source code. * Ryan Schmidt, Agustin Navarro, Ying-Chieh Liao, Adrian Bunk, Baruch Even, and Ronald Cole ported MDK to different platforms, and created and/or maintain packages for it. * Jason Uhlenkott, Andrew Hood, Radu Butnaru, Ruslan Batdalov, WeiZheng, Sascha Wilde, Michael Vernov and Xiaofeng Zhao reported bugs and suggested fixes to them. * Joshua Davies, Eli Bendersky, Milan Bella and Jens Seidel reported bugs on the documentation. * Christoph von Nathusius, Stephen Ramsay and Johan Swanljung tested MDK on different platforms, and helped fixing the configuration process in them. * Richard Stallman suggested various improvements to the documentation and has always kept an eye on each MDK release. * MDK was inspired by Darius Bacon's MIXAL program (http://www.accesscom.com/~darius/). 1 Installing MDK **************** 1.1 Download the source tarball =============================== GNU MDK is distributed as a source tarball available for download in the following URLs: * * GNU mirrors (http://www.gnu.org/prep/ftp.html) The above sites contain the latest stable releases of MDK. The development branch is available as a Git (http://git-scm.com/) repository located at(1) (*note Download-Footnote-1::) * After you have downloaded the source tarball, unpack it in a directory of your choice using the command: tar xfvz mdk-X.Y.tar.gz where X.Y stands for the downloaded version (the current stable release being version 1.3.0). (1) See MDK's Git page (https://savannah.gnu.org/git/?group=mdk) for more information on using the unstable source tree. Note, however, that the rest of this manual is about the _stable_ release. 1.2 Requirements ================ In order to build and install MDK, you will need the following libraries installed in your system: - GLIB 2.16.0 (http://www.gtk.org) (required) - GNU Flex 2.5 (http://www.gnu.org/software/flex/flex.html) (required) - GTK 2.16.0 (http://www.gtk.org) (optional) - Libglade 2.6.0 (http://ftp.gnome.org/pub/GNOME/sources/libglade/2.6/) (optional) - GNU Readline (http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html) (optional) - GNU Libguile 2.0 (http://www.gnu.org/software/guile) (optional) If present, readline and history are used to provide command completion and history management to the command line MIX virtual machine, 'mixvm'. GTK+ and libglade are needed if you want to build the graphical interface to the MIX virtual machine, 'gmixvm'. Finally, if libguile is found, the MDK utilities will be compiled with Guile support and will be extensible using Scheme. *Please note*: you need both the libraries _and_ the headers; this means both the library package and the '-dev' package if you do not compile your libraries yourself (ex: installing 'libgtk2.0-0' and 'libgtk2.0-0-dev' on Debian). 1.3 Basic installation ====================== MDK uses GNU Autoconf and Automake tools, and, therefore, should be built and installed without hassle using the following commands inside the source directory: ./configure make make install where the last one must be run as root. The first command, 'configure', will setup the makefiles for your system. In particular, 'configure' will look for GTK+ and libglade, and, if they are present, will generate the appropriate makefiles for building the 'gmixvm' graphical user interface. Upon completion, you should see a message with the configuration results like the following: *** GNU MDK 1.3.0 has been successfully configured. *** Type 'make' to build the following utilities: - mixasm (MIX assembler) - mixvm (MIX virtual machine, with readline support, with guile support) - gmixvm (mixvm GTK+ GUI, with guile support) - mixguile (the mixvm guile shell) where the last lines may be missing if you lack the above mentioned libraries. The next command, 'make', will actually build the MDK programs in the following locations: - 'mixutils/mixasm' - 'mixutils/mixvm' - 'mixgtk/gmixvm' - 'mixguile/mixguile' You can run these programs from within their directories, but I recommend you to install them in proper locations using 'make install' from a root shell. 1.4 Emacs support ================= MDK includes extensive support for Emacs. Upon installation, all the elisp code is installed in 'PREFIX/share/mdk', where 'PREFIX' stands for your installation root directory (e.g. '/usr/local'). You can copy the elisp files to a directory that is in your load-path, or you can add the above directory to it. Assuming that the installing prefix is '/usr/local', you can do it by adding to your '.emacs' file the following line: (setq load-path (cons "/usr/local/share/mdk" load-path)) 'MIXAL' programs can be written using Emacs and the elisp program 'share/mdk/mixal-mode.el', contributed by Pieter E. J. Pareit. It provides font locking, interactive help, compiling assistance and invocation of the 'MIX' virtual machine via a new major mode called 'mixal-mode'. To start 'mixal-mode' automatically whenever you edit a 'MIXAL' source file, add the following lines to your '.emacs' file: (autoload 'mixal-mode "mixal-mode" t) (add-to-list 'auto-mode-alist '("\\.mixal\\'" . mixal-mode)) In addition, 'mixvm' can be run within an Emacs GUD buffer using the elisp program 'share/mdk/mixvm.el', contributed by Philip E. King. 'mixvm.el' provides an interface between MDK's 'mixvm' and Emacs, via GUD. Place this file in your load-path, optionally adding the following line to your '.emacs' file: (autoload 'mixvm "mixvm" "mixvm/gud interaction" t) 1.5 Special configure flags =========================== You can fine-tune the configuration process using the following switches with configure: -- User Option: --enable-gui[=yes|no] -- User Option: --disable-gui Enables/disables the build of the MIX virtual machine GUI ('gmixvm'). If the required libraries are missing (*note Requirements::) the configure script with automatically disable this feature. -- User Option: --with-guile[=yes|no] -- User Option: --without-guile Enables/disables the Guile support for 'mixvm' and 'gmixvm', and the build of 'mixguile'. If the required libraries are missing (*note Requirements::) the configure script with automatically disable this feature. -- User Option: --with-readline[=yes|no] -- User Option: --without-readline Enables/disables the GNU Readline support for 'mixvm'. If the required libraries are missing (*note Requirements::) the configure script with automatically disable this feature. For additional, boilerplate configure options, see the 'INSTALL' file, or run configure --help 1.6 Supported platforms ======================= GNU MDK has been tested in the following platforms: * Debian GNU/Linux 2.2, 2.3, 3.0, 3.1, 3.2, 4.0, 5.0, 6.0, sid * Redhat GNU/Linux 8.0 (Ronald Cole), 7.0 (Agustin Navarro), 6.2 (Roberto Ferrero) * Mandrake 8.0 (Agustin Navarro) * FreeBSD 4.2, 4.3, 4.4, 4.5 (Ying-Chieh Liao), 5.2 * Solaris 2.8/gcc 2.95.3 (Stephen Ramsay) * MS Windows 98 SE/Cygwin 1.1.8-2 (Christoph von Nathusius)(1) (*note Supported platforms-Footnote-1::) * Mac OS X 10.1.2 (Johan Swanljung), Mac OS X 10.4.x, 10.5 (Darwin Port by Aleix Conchillo). * AMD Athlon, GNU/Linux version 2.4.2-2smp (Red Hat 7.1 (Seawolf)) (N. H. F. Beebe) * Apple PowerPC G3, GNU/Linux 2.2.18-4hpmac (Red Hat Linux/PPC 2000 Q4) (N. H. F. Beebe) * DEC Alpha, GNU/Linux 2.2.19-6.2.1 (Red Hat 6.2) (N. H. F. Beebe) * Compaq/DEC Alpha OSF/1 4.0F [ONLY after adding rsync's snprintf() implementation] (N. H. F. Beebe) * IBM PowerPC AIX 4.2 (N. H. F. Beebe) * Intel Pentium III, GNU/Linux 2.4.9-31smp (Red Hat 7.2 (Enigma)) (N. H. F. Beebe) * SGI Origin 200, IRIX 6.5 (N. H. F. Beebe) * Sun SPARC, GNU/Linux 2.2.19-6.2.1 (Red Hat 6.2) (N. H. F. Beebe) * Sun SPARC, Solaris 2.8 (N. H. F. Beebe) MDK will probably work on any GNU/Linux or BSD platform. If you try it in a platform not listed above, please send a mail to the author . (1) Caveats: Christoph has only tested 'mixvm' and 'mixasm' on this platform, using 'gcc' 2.95.3-2, 'GLIB' 1.2.10 and 'GNU readline' 4.1-2. He has reported missing history functionalities on a first try. If you find problems with history/readline functionality, please try a newer/manually installed readline version. 2 MIX and MIXAL tutorial ************************ In the book series 'The Art of Computer Programming', by D. Knuth, a virtual computer, the MIX, is used by the author (together with the set of binary instructions that the virtual CPU accepts) to illustrate the algorithms and skills that every serious programmer should master. Like any other real computer, there is a symbolic assembler language that can be used to program the MIX: the MIX assembly language, or MIXAL for short. In the following subsections you will find a tutorial on these topics, which will teach you the basics of the MIX architecture and how to program a MIX computer using MIXAL. 2.1 The MIX computer ==================== In this section, you will find a description of the MIX computer, its components and instruction set. 2.1.1 MIX architecture ---------------------- The basic information storage unit in the MIX computer is the "byte", which stores positive values in the range 0-63 . Note that a MIX byte can be then represented as 6 bits, instead of the common 8 bits for a _regular_ byte. Unless otherwise stated, we shall use the word "byte" to refer to a MIX 6-bit byte. A MIX "word" is defined as a set of 5 bytes plus a sign. The bytes within a word are numbered from 1 to 5, being byte number one the most significant one. The sign is denoted by index 0. Graphically, ----------------------------------------------- | 0 | 1 | 2 | 3 | 4 | 5 | ----------------------------------------------- | +/- | byte | byte | byte | byte | byte | ----------------------------------------------- Sample MIX words are '- 12 00 11 01 63' and '+ 12 11 34 43 00'. You can refer to subfields within a word using a "field specification" or "fspec" of the form "(L:R)", where L denotes the first byte, and R the last byte of the subfield. When L is zero, the subfield includes the word's sign. An fspec can also be represented as a single value 'F', given by 'F = 8*L + R' (thus the fspec '(1:3)', denoting the first three bytes of a word, is represented by the integer 11). The MIX computer stores information in "registers", that can store either a word or two bytes and sign (see below), and "memory cells", each one containing a word. Specifically, the MIX computer has 4000 memory cells with addresses 0 to 3999 (i.e., two bytes are enough to address a memory cell) and the following registers: 'rA' A register. General purpose register holding a word. Usually its contents serves as the operand of arithmetic and storing instructions. 'rX' X register. General purpose register holding a word. Often it acts as an extension or a replacement of 'rA'. 'rJ' J (jump) register. This register stores positive two-byte values, usually representing a jump address. 'rI1', 'rI2', 'rI3', 'rI4', 'rI5', 'rI6' Index registers. These six registers can store a signed two-byte value. Their contents are used as indexing values for the computation of effective memory addresses. In addition, the MIX computer contains: - An "overflow toggle" (a single bit with values "on" or "off"). In this manual, this toggle is denoted OV. - A "comparison indicator" (having three values: "EQUAL", "GREATER" or "LESS"). In this manual, this indicator is denoted CM, and its possible values are abbreviated as "E", "G" and "L". - Input-output block devices. Each device is labelled as 'un', where 'n' runs from 0 to 20. In Knuth's definition, 'u0' through 'u7' are magnetic tape units, 'u8' through '15' are disks and drums, 'u16' is a card reader, 'u17' is a card writer, 'u18' is a line printer and, 'u19' is a typewriter terminal, and 'u20', a paper tape. Our implementation maps these devices to disk files, except for 'u19', which represents the standard output. As noted above, the MIX computer communicates with the external world by a set of input-output devices which can be "connected" to it. The computer interchanges information using blocks of words whose length depends on the device at hand (*note Devices::). These words are interpreted by the device either as binary information (for devices 0-16), or as representing printable characters (devices 17-20). In the last case, each MIX byte is mapped onto a character according to the following table: 00 01 A 02 B 03 C 04 D 05 E 06 F 07 G 08 H 09 I 10 ~ 11 J 12 K 13 L 14 M 15 N 16 O 17 P 18 Q 19 R 20 [ 21 # 22 S 23 T 24 U 25 V 26 W 27 X 28 Y 29 Z 30 0 31 1 32 2 33 3 34 4 35 5 36 6 37 7 38 8 39 9 40 . 41 , 42 ( 43 ) 44 + 45 - 46 * 47 / 48 = 49 $ 50 < 51 > 52 @ 53 ; 54 : 55 ' The value 0 represents a whitespace. The characters '~', '[' and '#' correspond to symbols not representable as ASCII characters (uppercase delta, sigma and gamma, respectively), and byte values 56-63 have no associated character. Finally, the MIX computer features a virtual CPU which controls the above components, and which is able to execute a rich set of instructions (constituting its machine language, similar to those commonly found in real CPUs), including arithmetic, logical, storing, comparison and jump instructions. Being a typical von Neumann computer, the MIX CPU fetches binary instructions from memory sequentially (unless a jump instruction is found), and stores the address of the next instruction to be executed in an internal register called "location counter" (also known as program counter in other architectures). The next section, *Note MIX instruction set::, gives a complete description of the available MIX binary instructions. 2.1.2 MIX instruction set ------------------------- The following subsections fully describe the instruction set of the MIX computer. We begin with a description of the structure of binary instructions and the notation used to refer to their subfields. The remaining subsections are devoted to describing the actual instructions available to the MIX programmer. 2.1.2.1 Instruction structure ............................. MIX "instructions" are codified as words with the following subfield structure: _Subfield_ _fspec_ _Description_ ADDRESS (0:2) The first two bytes plus sign are the "address" field. Combined with the INDEX field, denotes the memory address to be used by the instruction. INDEX (3:3) The third byte is the "index", normally used for indexing the address(1) (*note Instruction structure-Footnote-1::). MOD (4:4) Byte four is used either as an operation code modifier or as a field specification. OPCODE (5:5) The last (least significant) byte in the word denotes the operation code. or, graphically, ------------------------------------------------ | 0 | 1 | 2 | 3 | 4 | 5 | ------------------------------------------------ | ADDRESS | INDEX | MOD | OPCODE | ------------------------------------------------ For a given instruction, 'M' stands for the memory address obtained after indexing the ADDRESS subfield (using its INDEX byte), and 'V' is the contents of the subfield indicated by MOD of the memory cell with address 'M'. For instance, suppose that we have the following contents of MIX registers and memory cells: [rI2] = + 00 63 [31] = - 10 11 00 11 22 where '[n]' denotes the contents of the nth memory cell and '[rI2]' the contents of register 'rI2'(2) (*note Instruction structure-Footnote-2::). Let us consider the binary instruction 'I = - 00 32 02 11 10'. For this instruction we have: ADDRESS = - 00 32 = -32 INDEX = 02 = 2 MOD = 11 = (1:3) OPCODE = 10 M = ADDRESS + [rI2] = -32 + 63 = 31 V = [M](MOD) = (- 10 11 00 11 22)(1:3) = + 00 00 10 11 00 Note that, when computing 'V' using a word and an fspec, we apply a left padding to the bytes selected by 'MOD' to obtain a complete word as the result. In the following subsections, we will assign to each MIX instruction a mnemonic, or symbolic name. For instance, the mnemonic of 'OPCODE' 10 is 'LD2'. Thus we can rewrite the above instruction as LD2 -32,2(1:3) or, for a generic instruction: MNEMONIC ADDRESS,INDEX(MOD) Some instructions are identified by both the OPCODE and the MOD fields. In these cases, the MOD will not appear in the above symbolic representation. Also when ADDRESS or INDEX are zero, they can be omitted. Finally, MOD defaults to (0:5) (meaning the whole word). (1) The actual memory address the instruction refers to, is obtained by adding to ADDRESS the value of the 'rI' register denoted by INDEX. (2) In general, '[X]' will denote the contents of entity 'X'; thus, by definition, 'V = [M](MOD)'. 2.1.2.2 Loading operators ......................... The following instructions are used to load memory contents into a register. 'LDA' Put in rA the contents of cell no. M. OPCODE = 8, MOD = fspec. 'rA <- V'. 'LDX' Put in rX the contents of cell no. M. OPCODE = 15, MOD = fspec. 'rX <- V'. 'LDi' Put in rIi the contents of cell no. M. OPCODE = 8 + i, MOD = fspec. 'rIi <- V'. 'LDAN' Put in rA the contents of cell no. M, with opposite sign. OPCODE = 16, MOD = fspec. 'rA <- -V'. 'LDXN' Put in rX the contents of cell no. M, with opposite sign. OPCODE = 23, MOD = fspec. 'rX <- -V'. 'LDiN' Put in rIi the contents of cell no. M, with opposite sign. OPCODE = 16 + i, MOD = fspec. 'rIi <- -V'. In all the above load instructions the 'MOD' field selects the bytes of the memory cell with address 'M' which are loaded into the requisite register (indicated by the 'OPCODE'). For instance, the word '+ 00 13 01 27 11' represents the instruction LD3 13,1(3:3) ^ ^ ^ ^ | | | | | | | --- MOD = 27 = 3*8 + 3 | | --- INDEX = 1 | --- ADDRESS = 00 13 --- OPCODE = 11 Let us suppose that, prior to this instruction execution, the state of the MIX computer is the following: [rI1] = - 00 01 [rI3] = + 24 12 [12] = - 01 02 03 04 05 As, in this case, 'M = 13 + [rI1] = 12', we have V = [M](3:3) = (- 01 02 03 04 05)(3:3) = + 00 00 00 00 03 (note that the specified subfield is left-padded with null bytes to complete a word). Hence, the MIX state, after the instruction execution, will be [rI1] = - 00 01 [rI3] = + 00 03 [12] = - 01 02 03 04 05 To further illustrate loading operators, the following table shows the contents of 'rX' after different 'LDX' instructions: 'LDX 12(0:0) [rX] = - 00 00 00 00 00' 'LDX 12(0:1) [rX] = - 00 00 00 00 01' 'LDX 12(3:5) [rX] = + 00 00 03 04 05' 'LDX 12(3:4) [rX] = + 00 00 00 03 04' 'LDX 12(0:5) [rX] = - 01 02 03 04 05' 2.1.2.3 Storing operators ......................... The following instructions are the inverse of the load operations: they are used to store a subfield of a register into a memory location. Here, MOD represents the subfield of the memory cell that is to be overwritten with bytes from a register. These bytes are taken beginning by the rightmost side of the register. 'STA' Store rA. OPCODE = 24, MOD = fspec. 'V <- rA'. 'STX' Store rX. OPCODE = 31, MOD = fspec. 'V <- rX'. 'STi' Store rIi. OPCODE = 24 + i, MOD = fspec. 'V <- rIi'. 'STJ' Store rJ. OPCODE = 32, MOD = fspec. 'V <- rJ'. 'STZ' Store zero. OPCODE = 33, MOD = fspec. 'V <- 0'. By way of example, consider the instruction 'STA 1200(2:3)'. It causes the MIX to fetch bytes no. 4 and 5 of register A and copy them to bytes 2 and 3 of memory cell no. 1200 (remember that, for these instructions, MOD specifies a subfield of _the memory address_). The other bytes of the memory cell retain their values. Thus, if prior to the instruction execution we have [1200] = - 20 21 22 23 24 [rA] = + 01 02 03 04 05 we will end up with [1200] = - 20 04 05 23 24 [rA] = + 01 02 03 04 05 As a second example, 'ST2 1000(0)' will set the sign of '[1000]' to that of '[rI2]'. 2.1.2.4 Arithmetic operators ............................ The following instructions perform arithmetic operations between rA and rX register and memory contents. 'ADD' Add and set OV if overflow. OPCODE = 1, MOD = fspec. 'rA <- rA +V'. 'SUB' Sub and set OV if overflow. OPCODE = 2, MOD = fspec. 'rA <- rA - V'. 'MUL' Multiply V times rA and store the 10-bytes product in rAX. OPCODE = 3, MOD = fspec. 'rAX <- rA x V'. 'DIV' rAX is considered a 10-bytes number, and it is divided by V. OPCODE = 4, MOD = fspec. 'rA <- rAX / V', 'rX' <- reminder. In all the above instructions, '[rA]' is one of the operands of the binary arithmetic operation, the other being 'V' (that is, the specified subfield of the memory cell with address 'M'), padded with zero bytes on its left-side to complete a word. In multiplication and division, the register 'X' comes into play as a right-extension of the register 'A', so that we are able to handle 10-byte numbers whose more significant bytes are those of 'rA' (the sign of this 10-byte number is that of 'rA': 'rX''s sign is ignored). Addition and subtraction of MIX words can give rise to overflows, since the result is stored in a register with room to only 5 bytes (plus sign). When this occurs, the operation result modulo 1,073,741,823 (the maximum value storable in a MIX word) is stored in 'rA', and the overflow toggle is set to TRUE. 2.1.2.5 Address transfer operators .................................. In these instructions, 'M' (the address of the instruction after indexing) is used as a number instead of as the address of a memory cell. Consequently, 'M' can have any valid word value (i.e., it's not limited to the 0-3999 range of a memory address). 'ENTA' Enter 'M' in [rA]. OPCODE = 48, MOD = 2. 'rA <- M'. 'ENTX' Enter 'M' in [rX]. OPCODE = 55, MOD = 2. 'rX <- M'. 'ENTi' Enter 'M' in [rIi]. OPCODE = 48 + i, MOD = 2. 'rIi <- M'. 'ENNA' Enter '-M' in [rA]. OPCODE = 48, MOD = 3. 'rA <- -M'. 'ENNX' Enter '-M' in [rX]. OPCODE = 55, MOD = 3. 'rX <- -M'. 'ENNi' Enter '-M' in [rIi]. OPCODE = 48 + i, MOD = 3. 'rIi <- -M'. 'INCA' Increase [rA] by 'M'. OPCODE = 48, MOD = 0. 'rA <- rA + M'. 'INCX' Increase [rX] by 'M'. OPCODE = 55, MOD = 0. 'rX <- rX + M'. 'INCi' Increase [rIi] by 'M'. OPCODE = 48 + i, MOD = 0. 'rIi <- rIi + M'. 'DECA' Decrease [rA] by 'M'. OPCODE = 48, MOD = 1. 'rA <- rA - M'. 'DECX' Decrease [rX] by 'M'. OPCODE = 55, MOD = 1. 'rX <- rX - M'. 'DECi' Decrease [rIi] by 'M'. OPCODE = 48 + i, MaOD = 0. 'rIi <- rIi - M'. In the above instructions, the subfield 'ADDRESS' acts as an immediate (indexed) operand, and allow us to set directly the contents of the MIX registers without an indirection to the memory cells (in a real CPU this would mean that they are faster that the previously discussed instructions, whose operands are fetched from memory). So, if you want to store in 'rA' the value -2000 (- 00 00 00 31 16), you can use the binary instruction + 31 16 00 03 48, or, symbolically, ENNA 2000 Used in conjunction with the store operations ('STA', 'STX', etc.), these instructions also allow you to set memory cells contents to concrete values. Note that in these address transfer operators, the 'MOD' field is not a subfield specificator, but serves to define (together with 'OPCODE') the concrete operation to be performed. 2.1.2.6 Comparison operators ............................ So far, we have learned how to move values around between the MIX registers and its memory cells, and also how to perform arithmetic operations using these values. But, in order to write non-trivial programs, other functionalities are needed. One of the most common is the ability to compare two values, which, combined with jumps, will allow the execution of conditional statements. The following instructions compare the value of a register with 'V', and set the CM indicator to the result of the comparison (i.e. to 'E', 'G' or 'L', equal, greater or lesser respectively). 'CMPA' Compare [rA] with V. OPCODE = 56, MOD = fspec. 'CMPX' Compare [rX] with V. OPCODE = 63, MOD = fspec. 'CMPi' Compare [rIi] with V. OPCODE = 56 + i, MOD = fspec. As explained above, these instructions modify the value of the MIX comparison indicator; but maybe you are asking yourself how do you use this value: enter jump operators, in the next subsection. 2.1.2.7 Jump operators ...................... The MIX computer has an internal register, called the "location counter", which stores the address of the next instruction to be fetched and executed by the virtual CPU. You cannot directly modify the contents of this internal register with a load instruction: after fetching the current instruction from memory, it is automatically increased in one unit by the MIX. However, there is a set of instructions (which we call jump instructions) which can alter the contents of the location counter provided some condition is met. When this occurs, the value of the next instruction address that would have been fetched in the absence of the jump is stored in 'rJ' (except for 'JSJ'), and the location counter is set to the value of 'M' (so that the next instruction is fetched from this new address). Later on, you can return to the point when the jump occurred reading the address stored in 'rJ'. The MIX computer provides the following jump instructions: With these instructions you force a jump to the specified address. Use 'JSJ' if you do not care about the return address. 'JMP' Unconditional jump. OPCODE = 39, MOD = 0. 'JSJ' Unconditional jump, but rJ is not modified. OPCODE = 39, MOD = 1. These instructions check the overflow toggle to decide whether to jump or not. 'JOV' Jump if OV is set (and turn it off). OPCODE = 39, MOD = 2. 'JNOV' Jump if OV is not set (and turn it off). OPCODE = 39, MOD = 3. In the following instructions, the jump is conditioned to the contents of the comparison flag: 'JL' Jump if '[CM] = L'. OPCODE = 39, MOD = 4. 'JE' Jump if '[CM] = E'. OPCODE = 39, MOD = 5. 'JG' Jump if '[CM] = G'. OPCODE = 39, MOD = 6. 'JGE' Jump if '[CM]' does not equal 'L'. OPCODE = 39, MOD = 7. 'JNE' Jump if '[CM]' does not equal 'E'. OPCODE = 39, MOD = 8. 'JLE' Jump if '[CM]' does not equal 'G'. OPCODE = 39, MOD = 9. You can also jump conditioned to the value stored in the MIX registers, using the following instructions: 'JAN' 'JAZ' 'JAP' 'JANN' 'JANZ' 'JANP' 'JAE' 'JAO' Jump if the content of rA is, respectively, negative, zero, positive, non-negative, non-zero, non-positive, even or odd. OPCODE = 40, MOD = 0, 1, 2, 3, 4, 5, 6, 7. 'JXN' 'JXZ' 'JXP' 'JXNN' 'JXNZ' 'JXNP' 'JXE' 'JXO' Jump if the content of rX is, respectively, negative, zero, positive, non-negative, non-zero, non-positive, even or odd. OPCODE = 47, MOD = 0, 1, 2, 3, 4, 5, 6, 7. 'JiN' 'JiZ' 'JiP' 'JiNN' 'JiNZ' 'JiNP' Jump if the content of rIi is, respectively, negative, zero, positive, non-negative, non-zero or non-positive. OPCODE = 40 + i, MOD = 0, 1, 2, 3, 4, 5. 2.1.2.8 Input-output operators .............................. As explained in previous sections (*note MIX architecture::), the MIX computer can interact with a series of block devices. To that end, you have at your disposal the following instructions: 'IN' Transfer a block of words from the specified unit to memory, starting at address M. OPCODE = 36, MOD = I/O unit. 'OUT' Transfer a block of words from memory (starting at address M) to the specified unit. OPCODE = 37, MOD = I/O unit. 'IOC' Perform a control operation (given by M) on the specified unit. OPCODE = 35, MOD = I/O unit. 'JRED' Jump to M if the specified unit is ready. OPCODE = 38, MOD = I/O unit. 'JBUS' Jump to M if the specified unit is busy. OPCODE = 34, MOD = I/O unit. In all the above instructions, the 'MOD' subfile must be in the range 0-20, since it denotes the operation's target device. The 'IOC' instruction makes sense for magnetic tape devices ('MOD' = 0-7): it shifts the read/write pointer by the number of blocks given by 'M' (if it equals zero, the tape is rewound), paper tape devices ('MOD' = 20): 'M' should be 0, the tape is rewound, and disk/drum devices ('MOD' = 8-15): it moves the read/write pointer to the block specified in rX and 'M' should be 0(1) (*note Input-output operators-Footnote-1::). (1) In Knuth's original definition, there are other control operations available, but they do not make sense when implementing the devices as disk files (as we do in MDK simulator). For the same reason, MDK devices are always ready, since all input-output operations are performed using synchronous system calls. 2.1.2.9 Conversion operators ............................ The following instructions convert between numerical values and their character representations. 'NUM' Convert rAX, assumed to contain a character representation of a number, to its numerical value and store it in rA. OPCODE = 5, MOD = 0. 'CHAR' Convert the number stored in rA to a character representation and store it in rAX. OPCODE = 5, MOD = 1. Digits are represented in MIX by the range of values 30-39 (digits 0-9). Thus, if the contents of 'rA' and 'rX' are, for instance, [rA] = + 30 30 31 32 33 [rX] = + 31 35 39 30 34 the represented number is 0012315904, and 'NUM' will store this value in 'rA' (i.e., we end up with '[rA]' = + 0 46 62 52 0 = 12315904). If any byte in 'rA' or 'rB' does not belong to the range 30-39, it is interpreted by 'NUM' as the digit obtained by taking its value modulo 10. E.g. values 0, 10, 20, 30, 40, 50, 60 all represent the digit 0; 2, 12, 22, etc. represent the digit 2, and so on. For instance, the number 0012315904 mentioned above could also be represented as [rA] = + 10 40 31 52 23 [rX] = + 11 35 49 20 54 'CHAR' performs the inverse operation, using only the values 30 to 39 for representing digits 0-9. 2.1.2.10 Shift operators ........................ The following instructions perform byte-wise shifts of the contents of 'rA' and 'rX'. 'SLA' 'SRA' 'SLAX' 'SRAX' 'SLC' 'SRC' Shift rA or rAX left, right, or rAX circularly (see example below) left or right. M specifies the number of bytes to be shifted. OPCODE = 6, MOD = 0, 1, 2, 3, 4, 5. The following instructions perform binary shifts of the contents of 'rA' and 'rX'. 'SLB' 'SRB' Shift rAX left or right binary. M specifies the number of binary places to shift. OPCODE = 6, MOD = 6, 7 If we begin with, say, '[rA]' = - 01 02 03 04 05, we would have the following modifications to 'rA' contents when performing the instructions on the left column: SLA 2 [rA] = - 03 04 05 00 00 SLA 6 [rA] = - 00 00 00 00 00 SRA 1 [rA] = - 00 01 02 03 04 Note that the sign is unaffected by shift operations. On the other hand, 'SLC', 'SRC', 'SLAX', 'SRAX', 'SLB' and 'SRB' treat 'rA' and 'rX' as a single 10-bytes register (ignoring again the signs). For instance, if we begin with '[rA]' = + 01 02 03 04 05 and '[rX]' = - 06 07 08 09 10, we would have: SLC 3 [rA] = + 04 05 06 07 08 [rX] = - 09 10 01 02 03 SLAX 3 [rA] = + 04 05 06 07 08 [rX] = - 09 10 00 00 00 SRC 4 [rA] = + 07 08 09 10 01 [rX] = - 02 03 04 05 06 SRAX 4 [rA] = + 00 00 00 00 01 [rX] = - 02 03 04 05 06 SLB 1 [rA] = + 02 04 06 08 10 [rX] = - 12 14 16 18 20 2.1.2.11 Miscellaneous operators ................................ Finally, we list in the following table three miscellaneous MIX instructions which do not fit in any of the previous subsections: 'MOVE' Move MOD words from M to the location stored in rI1. OPCODE = 7, MOD = no. of words. 'NOP' No operation. OPCODE = 0, MOD = 0. 'HLT' Halt. Stops instruction fetching. OPCODE = 5, MOD = 2. The only effect of executing 'NOP' is increasing the location counter, while 'HLT' usually marks program termination. 2.1.2.12 Execution times ........................ When writing MIXAL programs (or any kind of programs, for that matter), we shall often be interested in their execution time. Loosely speaking, we will be interested in the answer to the question: how long does it take a program to execute? Of course, this execution time will be a function of the input size, and the answer to our question is commonly given as the asymptotic behaviour as a function of the input size. At any rate, to compute this asymptotic behaviour, we need a measure of how long execution of a single instruction takes in our (virtual) CPU. Therefore, each MIX instruction will have an associated execution time, given in arbitrary units (in a real computer, the value of this unit will depend on the hardware configuration). When our MIX virtual machine executes programs, it will (optionally) give you the value of their execution time based upon the execution time of each single instruction. In the following table, the execution times (in the above mentioned arbitrary units) of the MIX instructions are given. 'NOP' 1 'ADD' 2 'SUB' 2 'MUL' 10 'DIV' 12 'NUM' 10 'CHAR' 10 'HLT' 10 'SLx' 2 'SRx' 2 'LDx' 2 'STx' 2 'JBUS' 1 'IOC' 1 'IN' 1 'OUT' 1 'JRED' 1 'Jx' 1 'INCx' 1 'DECx' 1 'ENTx' 1 'ENNx' 1 'CMPx' 1 'MOVE' 1+2F In the above table, 'F' stands for the number of blocks to be moved (given by the 'FSPEC' subfield of the instruction); 'SLx' and 'SRx' are a short cut for the byte-shifting operations; 'LDx' denote all the loading operations; 'STx' are the storing operations; 'Jx' stands for all the jump operations, and so on with the rest of abbreviations. 2.2 MIXAL ========= In the previous sections we have listed all the available MIX binary instructions. As we have shown, each instruction is represented by a word which is fetched from memory and executed by the MIX virtual CPU. As is the case with real computers, the MIX knows how to decode instructions in binary format (the so-called machine language), but a human programmer would have a tough time if she were to write her programs in machine language. Fortunately, the MIX computer can be programmed using an assembly language, MIXAL, which provides a symbolic way of writing the binary instructions understood by the imaginary MIX computer. If you have used assembler languages before, you will find MIXAL a very familiar language. MIXAL source files are translated to machine language by a MIX assembler, which produces a binary file (the actual MIX program) which can be directly loaded into the MIX memory and subsequently executed. In this section, we describe MIXAL, the MIX assembly language. The implementation of the MIX assembler program and MIX computer simulator provided by MDK are described later on (*note Getting started::). 2.2.1 Basic program structure ----------------------------- The MIX assembler reads MIXAL files line by line, producing, when required, a binary instruction, which is associated to a predefined memory address. To keep track of the current address, the assembler maintains an internal location counter which is incremented each time an instruction is compiled. In addition to MIX instructions, you can include in MIXAL file assembly directives (or pseudoinstructions) addressed at the assembler itself (for instance, telling it where the program starts and ends, or to reposition the location counter; see below). MIX instructions and assembler directives(1) (*note Basic structure-Footnote-1::) are written in MIXAL (one per source file line) according to the following pattern: [LABEL] MNEMONIC [OPERAND] [COMMENT] where 'OPERAND' is of the form [ADDRESS][,INDEX][(MOD)] Items between square brackets are optional, and 'LABEL' is an alphanumeric identifier (a "symbol") which gets the current value of the location counter, and can be used in subsequent expressions, 'MNEMONIC' is a literal denoting the operation code of the instruction (e.g. 'LDA', 'STA'; see *note MIX instruction set::) or an assembly pseudoinstruction (e.g. 'ORIG', 'EQU'), 'ADDRESS' is an expression evaluating to the address subfield of the instruction, 'INDEX' is an expression evaluating to the index subfield of the instruction, which defaults to 0 (i.e., no use of indexing) and can only be used when 'ADDRESS' is present, 'MOD' is an expression evaluating to the mod subfield of the instruction. Its default value, when omitted, depends on 'OPCODE', 'COMMENT' any number of spaces after the operand mark the beginning of a comment, i.e. any text separated by white space from the operand is ignored by the assembler (note that spaces are not allowed within the 'OPERAND' field). Note that spaces are _not_ allowed between the 'ADDRESS', 'INDEX' and 'MOD' fields if they are present. White space is used to separate the label, operation code and operand parts of the instruction(2) (*note Basic structure-Footnote-2::). We have already listed the mnemonics associated with each MIX instruction; sample MIXAL instructions representing MIX instructions are: HERE LDA 2000 HERE represents the current location counter LDX HERE,2(1:3) this is a comment JMP 1234 (1) We shall call them, collectively, MIXAL instructions. (2) In fact, Knuth's definition of MIXAL restricts the column number at which each of these instruction parts must start. The MIXAL assembler included in MDK, 'mixasm', does not impose such restriction. 2.2.2 MIXAL directives ---------------------- MIXAL instructions can be either one of the MIX machine instructions (*note MIX instruction set::) or one of the following assembly pseudoinstructions: 'ORIG' Sets the value of the memory address to which following instructions will be allocated after compilation. 'EQU' Used to define a symbol's value, e.g. 'SYM EQU 2*200/3'. 'CON' The value of the given expression is copied directly into the current memory address. 'ALF' Takes as operand five characters, constituting the five bytes of a word which is copied directly into the current memory address. 'END' Marks the end of the program. Its operand gives the start address for program execution. The operand of 'ORIG', 'EQU', 'CON' and 'END' can be any expression evaluating to a constant MIX word, i.e., either a simple MIXAL expression (composed of numbers, symbols and binary operators, *note Expressions::) or a w-expression (*note W-expressions::). All MIXAL programs must contain an 'END' directive, with a twofold end: first, it marks the end of the assembler job, and, in the second place, its (mandatory) operand indicates the start address for the compiled program (that is, the address at which the virtual MIX machine must begin fetching instructions after loading the program). It is also very common (although not mandatory) to include at least an 'ORIG' directive to mark the initial value of the assembler's location counter (remember that it stores the address associated with each compiled MIX instruction). Thus, a minimal MIXAL program would be ORIG 2000 set the initial compilation address NOP this instruction will be loaded at address 2000 HLT and this one at address 2001 END 2000 end of program; start at address 2000 this line is not parsed by the assembler The assembler will generate two binary instructions ('NOP' (+ 00 00 00 00 00) and 'HLT' (+ 00 00 02 05)), which will be loaded at addresses 2000 and 2001. Execution of the program will begin at address 2000. Every MIXAL program should also include a 'HLT' instruction, which will mark the end of program execution (but not of program compilation). The 'EQU' directive allows the definition of symbolic names for specific values. For instance, we could rewrite the above program as follows: START EQU 2000 ORIG START NOP HLT END START which would give rise to the same compiled code. Symbolic constants (or symbols, for short) can also be implicitly defined placing them in the 'LABEL' field of a MIXAL instruction: in this case, the assembler assigns to the symbol the value of the location counter before compiling the line. Hence, a third way of writing our trivial program is ORIG 2000 START NOP HLT END START The 'CON' directive allows you to directly specify the contents of the memory address pointed by the location counter. For instance, when the assembler encounters the following code snippet ORIG 1150 CON -1823473 it will assign to the memory cell number 1150 the contents - 00 06 61 11 49 (which corresponds to the decimal value -1823473). Finally, the 'ALF' directive lets you specify the memory contents as a set of five (optionally quoted) characters, which are translated by the assembler to their byte values, conforming in that way the binary word that is to be stored in the corresponding memory cell. This directive comes in handy when you need to store printable messages in a memory address, as in the following example (1) (*note MIXAL directives-Footnote-1::): OUT MSG MSG is not yet defined here (future reference) MSG ALF "THIS " MSG gets defined here ALF "IS A " ALF "MESSA" ALF "GE. " The above snippet also shows the use of a "future reference", that is, the usage of a symbol ('MSG' in the example) prior of its actual definition. The MIXAL assembler is able to handle future references subject to some limitations which are described in the following section (*note Expressions::). Any line starting with an asterisk is treated as a comment and ignored by the assembler. * This is a comment: this line is ignored. * This line is an error: * must be in column 1. As noted in the previous section, comments can also be located after the 'OPERAND' field of an instruction, separated from it by white space, as in LABEL LDA 100 This is also a comment (1) In the original MIXAL definition, the 'ALF' argument is not quoted. You can write the operand (as the 'ADDRESS' field) without quotes, but, in this case, you must follow the alignment rules of the original MIXAL definition (namely, the 'ADDRESS' must start at column 17). 2.2.3 Expressions ----------------- The 'ADDRESS', 'INDEX' and 'MOD' fields of a MIXAL instruction can be expressions, formed by numbers, identifiers and binary operators ('+ - * / // :'). '+' and '-' can also be used as unary operators. Operator precedence is from left to right: there is no other operator precedence rule, and parentheses cannot be used for grouping. A stand-alone asterisk denotes the current memory location; thus, for instance, 4+2** evaluates to 6 (4 plus 2) times the current memory location. White space is not allowed within expressions. The special binary operator ':' has the same meaning as in fspecs, i.e., A:B = 8*A + B while 'A//B' stands for the quotient of the ten-byte number 'A' 00 00 00 00 00 (that is, A right-padded with 5 null bytes or, what amounts to the same, multiplied by 64 to the fifth power) divided by 'B'. Sample expressions are: 18-8*3 = 30 14/3 = 4 1+3:11 = 4:11 = 43 1//64 = (01 00 00 00 00 00)/(00 00 00 01 00) = (01 00 00 00 00) Note that all MIXAL expressions evaluate to a MIX word (by definition). All symbols appearing within an expression must be previously defined. Future references are only allowed when appearing standalone (or modified by an unary operator) in the 'ADDRESS' part of a MIXAL instruction, e.g. * OK: stand alone future reference STA -S1(1:5) * ERROR: future reference in expression LDX 2-S1 S1 LD1 2000 2.2.4 W-expressions ------------------- Besides expressions, as described above (*note Expressions::), the MIXAL assembler is able to handle the so called "w-expressions" as the operands of the directives 'ORIG', 'EQU', 'CON' and 'END' (*note MIXAL directives::). The general form of a w-expression is the following: WEXP = EXP[(EXP)][,WEXP] where 'EXP' stands for an expression and square brackets denote optional items. Thus, a w-expression is made by an expression, followed by an optional expression between parenthesis, followed by any number of similar constructs separated by commas. Sample w-expressions are: 2000 235(3) S1+3(S2),3000 S1,S2(3:5),23 W-expressions are evaluated from left to right as follows: * Start with an accumulated result 'w' equal to 0. * Take the first expression of the comma-separated list and evaluate it. For instance, if the w-expression is 'S1+2(2:4),2000(S2)', we evaluate first 'S1+2'; let's suppose that 'S1' equals 265230: then 'S1+2 = 265232 = + 00 01 00 48 16'. * Evaluate the expression within parenthesis, reducing it to an f-spec of the form 'L:R'. In our previous example, the expression between parenthesis already has the desired form: 2:4. * Substitute the bytes of the accumulated result 'w' designated by the f-spec using those of the previous expression value. In our sample, 'w = + 00 00 00 00 00', and we must substitute bytes 2, 3 and 4 of 'w' using values from 265232. We need 3 bytes, and we take the least significant ones: 00, 48, and 16, and insert them in positions 2, 3 and 4 of 'w', obtaining 'w = + 00 00 48 16 00'. * Repeat this operation with the remaining terms, acting on the new value of 'w'. In our example, if, say, 'S2 = 1:1', we must substitute the first byte of 'w' using one byte (the least significant) from 2000, that is, 16 (since 2000 = + 00 00 00 31 16) and, therefore, we obtain 'w = + 16 00 48 16 00'; summing up, we have obtained '265232(1:4),2000(1:1) = + 16 00 48 16 00 = 268633088'. As a second example, in the w-expression 1(1:2),66(4:5) we first take two bytes from 1 (00 and 01) and store them as bytes 1 and 2 of the result (obtaining '+ 00 01 00 00 00') and, afterwards, take two bytes from 66 (01 and 02) and store them as bytes 4 and 5 of the result, obtaining '+ 00 01 00 01 02' (262210). The process is repeated for each new comma-separated example. For instance: 1(1:1),2(2:2),3(3:3),4(4:4) = 01 02 03 04 00 As stated before, w-expressions can only appear as the operands of MIXAL directives taking a constant value ('ORIG', 'EQU', 'CON' and 'END'). Future references are _not_ allowed within w-expressions (i.e., all symbols appearing in a w-expression must be defined before it is used). 2.2.5 Local symbols ------------------- Besides user defined symbols, MIXAL programmers can use the so called "local symbols", which are symbols of the form '[1-9][HBF]'. A local symbol 'nB' refers to the address of the last previous occurrence of 'nH' as a label, while 'nF' refers to the next 'nH' occurrence. Unlike user defined symbols, 'nH' can appear multiple times in the 'LABEL' part of different MIXAL instructions. The following code shows an instance of local symbols' usage: * line 1 1H LDA 100 * line 2: 1B refers to address of line 1, 3F refers to address of line 4 STA 3F,2(1B//2) * line 3: redefinition of 1H 1H STZ * line 4: 1B refers to address of line 3 3H JMP 1B Note that a 'B' local symbol never refers to a definition in its own line, that is, in the following program: ORIG 1999 ST NOP 3H EQU 69 3H ENTA 3B local symbol 3B refers to 3H in previous line HLT END ST the contents of 'rA' is set to 69 and _not_ to 2001. An specially tricky case occurs when using local symbols in conjunction with 'ORIG' pseudoinstructions. To wit(1) (*note Local symbols-Footnote-1::), ORIG 1999 ST NOP 3H CON 10 ENT1 * LDA 3B ** rI1 is 2001, rA is 10. So far so good! 3H ORIG 3B+1000 ** at this point 3H equals 2003 ** and the location counter equals 3000. ENT2 * LDX 3B ** rI2 contains 3000, rX contains 2003. HLT END ST (1) The author wants to thank Philip E. King for pointing these two special cases of local symbol usage to him. 2.2.6 Literal constants ----------------------- MIXAL allows the introduction of "literal constants", which are automatically stored in memory addresses after the end of the program by the assembler. Literal constants are denoted as '=wexp=', where 'wexp' is a w-expression (*note W-expressions::). For instance, the code L EQU 5 LDA =20-L= causes the assembler to add after the program's end an instruction with contents 15 ('20-L'), and to assemble the above code as the instruction ' LDA a', where 'a' stands for the address in which the value 15 is stored. In other words, the compiled code is equivalent to the following: L EQU 5 LDA a ... a CON 20-L END start 3 Getting started ***************** In this chapter, you will find a sample code-compile-run-debug session using the MDK utilities. Familiarity with the MIX mythical computer and its assembly language MIXAL (as described in Knuth's TAOCP) is assumed; for a compact reminder, see *note MIX and MIXAL tutorial::. 3.1 Writing a source file ========================= MIXAL programs can be written as ASCII files with your editor of choice. Here you have the mandatory _hello world_ as written in the MIXAL assembly language: * (1) * hello.mixal: say 'hello world' in MIXAL (2) * (3) * label ins operand comment (4) TERM EQU 19 the MIX console device number (5) ORIG 3000 start address (6) START OUT MSG(TERM) output data at address MSG (7) HLT halt execution (8) MSG ALF "MIXAL" (9) ALF " HELL" (10) ALF "O WOR" (11) ALF "LD " (12) END START end of the program (13) MIXAL source files should have the extension '.mixal' when used with the MDK utilities. As you can see in the above sample, each line in a MIXAL file can be divided into four fields separated by an arbitrary amount of whitespace characters (blanks and or tabs). While in Knuth's definition of MIXAL each field must start at a fixed pre-defined column number, the MDK assembler loosens this requirement and lets you format the file as you see fit. The only restrictions retained are for comment lines (like 1-4) which must begin with an asterisk (*) placed at column 1, and for the label field (see below) which, if present, must also start at column 1. The four fields in each non-comment line are: - an optional label, which either refers to the current memory address (as 'START' and 'MSG' in lines 7 and 9) or a defined symbol ('TERM') (if present, the label must always start at the first column in its line, for the first whitespace in the line marks the beginning of the second field), - an operation mnemonic, which can represent either a MIX instruction ('OUT' and 'HLT' in lines 7 and 8 above), or an assembly pseudoinstruction (e.g., the 'ORIG' pseudoinstruction in line 6(1) (*note Writing a source file-Footnote-1::). - an optional operand for the (pseudo)instruction, and - an optional free text comment. Lines 9-12 of the 'hello.mixal' file above also show the second (and last) difference between Knuth's MIXAL definition and ours: the operand of the 'ALF' pseudoinstruction (a word of five characters) must be quoted using ""(2) (*note Writing a source file-Footnote-2::). The workings of this sample program should be straightforward if you are familiar with MIXAL. See TAOCP vol. 1 for a thorough definition or *note MIX and MIXAL tutorial::, for a tutorial. (1) If an 'ORIG' directive is not used, the program will be loaded by the virtual machine at address 0. 'ORIG' allows allocating the executable code where you see fit. (2) In Knuth's definition, the operand always starts at a fixed column number, and the use of quotation is therefore unnecessary. As 'mixasm' releases this requirement, marking the beginning and end of the 'ALF' operand disambiguates the parser's recognition of this operand when it includes blanks. Note that double-quotes (") are not part of the MIX character set, and, therefore, no escape characters are needed within 'ALF''s operands. 3.2 Compiling ============= Three simulators of the MIX computer, called 'mixvm', 'gmixvm' and 'mixguile', are included in the MDK tools. They are able to run binary files containing MIX instructions written in their binary representation. You can translate MIXAL source files into this binary form using 'mixasm', the MIXAL assembler. So, in order to compile the 'hello.mixal' file, you can type the following command at your shell prompt: mixasm hello If the source file contains no errors, this will produce a binary file called 'hello.mix' which can be loaded and run by the MIX virtual machine. Unless the 'mixasm' option '-O' is provided, the assembler will include debug information in the executable file (for a complete description of all the compilation options, see *note mixasm::). Now, your are ready to run your first MIX program, as described in the following section. 3.3 Running the program ======================= MIX is a mythical computer, so it is no use ordering it from your favorite hardware provider. MDK provides three software simulators of the computer, though. They are * 'mixvm', a command line oriented simulator, * 'gmixvm', a GTK based graphical interface to 'mixvm', and * 'mixguile', a Guile shell with a built-in MIX simulator. All three simulators accept the same set of user commands, but offer a different user interface, as noted above. In this section we shall describe some of these commands, and show you how to use them from 'mixvm''s command line. You can use them as well at 'gmixvm''s command prompt (*note gmixvm::), or using the built-in Scheme primitives of 'mixguile' (*note Using mixguile::). Using the MIX simulators, you can run your MIXAL programs, after compiling them with 'mixasm' into binary '.mix' files. 'mixvm' can be used either in "interactive" or "non-interactive" mode. In the second case, 'mixvm' will load your program into memory, execute it (producing any output due to MIXAL 'OUT' instructions present in the program), and exit when it encounters a 'HLT' instruction. In interactive mode, you will enter a shell prompt which allows you issuing commands to the running virtual machine. These commands will permit you to load, run and debug programs, as well as to inspect the MIX computer state (register contents, memory cells contents and so on). 3.3.1 Non-interactive mode -------------------------- To make 'mixvm' work in non-interactive mode, use the '-r' flag. Thus, to run our 'hello.mix' program, simply type mixvm -r hello at your command prompt, and you will get the following output: MIXAL HELLO WORLD Since our hello world program uses MIX's device number 19 as its output device (*note Writing a source file::), the output is redirected to the shell's standard output. Had you used any other MIX output devices (disks, drums, line printer, etc.), 'mixvm' would have created a file named after the device used (e.g. 'disk4.dev') and written its output there(1) (*note Non-interactive mode-Footnote-1::). The virtual machine can also report the execution time of the program, according to the (virtual) time spent in each of the binary instructions (*note Execution times::). Printing of execution time statistics is activated with the '-t' flag; running mixvm -t -r hello produces the following output: MIXAL HELLO WORLD ** Execution time: 11 Sometimes, you will prefer to store the results of your program in MIX registers rather than writing them to a device. In such cases, 'mixvm''s '-d' flag is your friend: it makes 'mixvm' dump the contents of its registers and flags after executing the loaded program. For instance, typing the following command at your shell's prompt mixvm -d -r hello you will obtain the following output: MIXAL HELLO WORLD rA: + 00 00 00 00 00 (0000000000) rX: + 00 00 00 00 00 (0000000000) rJ: + 00 00 (0000) rI1: + 00 00 (0000) rI2: + 00 00 (0000) rI3: + 00 00 (0000) rI4: + 00 00 (0000) rI5: + 00 00 (0000) rI6: + 00 00 (0000) Overflow: F Cmp: E which, in addition to the program's outputs and execution time, gives you the contents of the MIX registers and the values of the overflow toggle and comparison flag (admittedly, rather uninteresting in our sample). As you can see, running programs non-interactively has many limitations. You cannot peek the virtual machine's memory contents, not to mention stepping through your program's instructions or setting breakpoints(2) (*note Non-interactive mode-Footnote-2::). Enter interactive mode. (1) The device files are stored, by default, in a directory called '.mdk', which is created in your home directory the first time 'mixvm' is run. You can change this default directory using the command 'devdir' when running 'mixvm' in interactive mode (*note Configuration commands::) (2) The 'mixguile' program allows you to execute arbitrary combinations of 'mixvm' commands (using Scheme) non-interactively. *Note Scheme scripts::. 3.3.2 Interactive mode ---------------------- To enter the MIX virtual machine interactive mode, simply type mixvm at your shell command prompt. This command enters the 'mixvm' command shell. You will be presented the following command prompt: MIX > The virtual machine is initialised and ready to accept your commands. The 'mixvm' command shell uses GNU's readline, so that you have at your disposal command completion (using ) and history functionality, as well as other line editing shortcuts common to all utilities using this library (for a complete description of readline's line editing usage, see *note (Readline)Command Line Editing::.) Usually, the first thing you will want to do is loading a compiled MIX program into memory. This is accomplished by the 'load' command, which takes as an argument the name of the '.mix' file to be loaded. Thus, typing MIX > load hello Program loaded. Start address: 3000 MIX > will load 'hello.mix' into the virtual machine's memory and set the program counter to the address of the first instruction. You can obtain the contents of the program counter using the command 'pc': MIX > pc Current address: 3000 MIX > After loading it, you are ready to run the program, using, as you surely have guessed, the 'run' command: MIX > run Running ... MIXAL HELLO WORLD ... done Elapsed time: 11 /Total program time: 11 (Total uptime: 11) MIX > Note that now the timing statistics are richer. You obtain the elapsed execution time (i.e., the time spent executing instructions since the last breakpoint), the total execution time for the program up to now (which in our case coincides with the elapsed time, since there were no breakpoints), and the total uptime for the virtual machine (you can load and run more than one program in the same session)(1) (*note Interactive mode-Footnote-1::). After running the program, the program counter will point to the address after the one containing the 'HLT' instruction. In our case, asking the value of the program counter after executing the program will give us MIX > pc Current address: 3002 MIX > You can check the contents of a memory cell giving its address as an argument of the command 'pmem', like this MIX > pmem 3001 3001: + 00 00 00 02 05 (0000000133) MIX > and convince yourself that address 3001 contains the binary representation of the instruction 'HLT'. An address range of the form FROM-TO can also be used as the argument of 'pmem': MIX > pmem 3000-3006 3000: + 46 58 00 19 37 (0786957541) 3001: + 00 00 00 02 05 (0000000133) 3002: + 14 09 27 01 13 (0237350989) 3003: + 00 08 05 13 13 (0002118477) 3004: + 16 00 26 16 19 (0268542995) 3005: + 13 04 00 00 00 (0219152384) 3006: + 00 00 00 00 00 (0000000000) MIX > In a similar manner, you can look at the contents of the MIX registers and flags. For instance, to ask for the contents of the A register you can type MIX > preg A rA: + 00 00 00 00 00 (0000000000) MIX > Use the command 'help' to obtain a list of all available commands, and 'help COMMAND' for help on a specific command, e.g. MIX > help run run Run loaded or given MIX code file. Usage: run [FILENAME] MIX > For a complete list of commands available at the MIX propmt, *Note mixvm::. In the following subsection, you will find a quick tour over commands useful for debugging your programs. (1) Printing of timing statistics can be disabled using the command 'timing' (*note Configuration commands::). 3.3.3 Debugging commands ------------------------ The interactive mode of 'mixvm' lets you step by step execution of programs as well as breakpoint setting. Use 'next' to step through the program, running its instructions one by one. To run our two-instruction 'hello.mix' sample you can do the following: MIX > load hello Program loaded. Start address: 3000 MIX > pc Current address: 3000 MIX > next MIXAL HELLO WORLD Elapsed time: 1 /Total program time: 1 (Total uptime: 1) MIX > pc Current address: 3001 MIX > next End of program reached at address 3002 Elapsed time: 10 /Total program time: 11 (Total uptime: 11) MIX > pc Current address: 3002 MIX > next MIXAL HELLO WORLD Elapsed time: 1 /Total program time: 1 (Total uptime: 12) MIX > MIX > run Running ... ... done Elapsed time: 10 /Total program time: 11 (Total uptime: 22) MIX > (As an aside, the above sample also shows how the virtual machine handles cumulative time statistics and automatic program restart). You can set a breakpoint at a given address using the command 'sbpa' (set breakpoint at address). When a breakpoint is set, 'run' will stop before executing the instruction at the given address. Typing 'run' again will resume program execution. Coming back to our hello world example, we would have: MIX > sbpa 3001 Breakpoint set at address 3001 MIX > run Running ... MIXAL HELLO WORLD ... stopped: breakpoint at line 8 (address 3001) Elapsed time: 1 /Total program time: 1 (Total uptime: 23) MIX > run Running ... ... done Elapsed time: 10 /Total program time: 11 (Total uptime: 33) MIX > Note that, since we compiled 'hello.mixal' with debug info enabled, the virtual machine is able to tell us the line in the source file corresponding to the breakpoint we are setting. As a matter of fact, you can directly set breakpoints at source code lines using the command 'sbp LINE_NO', e.g. MIX > sbp 4 Breakpoint set at line 7 MIX > 'sbp' sets the breakpoint at the first meaningful source code line; thus, in the above example we have requested a breakpoint at a line which does not correspond to a MIX instruction and the breakpoint is set at the first line containing a real instruction after the given one. To unset breakpoints, use 'cbpa ADDRESS' and 'cbp LINE_NO', or 'cabp' to remove all currently set breakpoints. You can also set conditional breakpoints, i.e., tell 'mixvm' to interrupt program execution whenever a register, a memory cell, the comparison flag or the overflow toggle change using the commands 'sbp[rmco]' (*note Debug commands::). MIXAL lets you define symbolic constants, either using the 'EQU' pseudoinstruction or starting an instruction line with a label (which assigns to the label the value of the current memory address). Each MIXAL program has, therefore, an associated symbol table which you can inspect using the 'psym' command. For our hello world sample, you will obtain the following output: MIX > psym START: 3000 TERM: 19 MSG: 3002 MIX > Other useful commands for debugging are 'strace' (which turns on tracing of executed instructions), 'pbt' (which prints a backtrace of executed instructions) and 'weval' (which evaluates w-expressions on the fly). For a complete description of all available MIX commands, *Note mixvm::. 3.4 Using 'mixguile' ==================== With 'mixguile' you can run a MIX simulator embedded in a Guile shell, that is, using Scheme functions and programs. As with 'mixvm', 'mixguile' can be run both in interactive and non-interactive modes. The following subsections provide a quick tour on using this MIX emulator. 3.4.1 The 'mixguile' shell -------------------------- If you simply type mixguile at the command prompt, you'll be presented a Guile shell prompt like this guile> At this point, you have entered a Scheme read-eval-print loop (REPL) which offers you all the Guile functionality plus a new set of built-in procedures to execute and debug MIX programs. Each of the 'mixvm' commands described in the previous sections (and in *note mixvm::) have a Scheme function counterpart named after it by prepending the prefix 'mix-' to its name. Thus, to load our hello world program, you can simply enter guile> (mix-load "hello") Program loaded. Start address: 3000 guile> and run it using 'mix-run': guile> (mix-run) Running ... MIXAL HELLO WORLD ... done Elapsed time: 11 /Total program time: 11 (Total uptime: 11) guile> In the same way, you can execute it step by step using the Scheme function 'mix-next' or set a breakpoint: guile> (mix-sbp 4) Breakpoint set at line 5 guile> or, if you one to peek at a register contents: guile> (mix-preg 'A) rA: + 00 00 00 00 00 (0000000000) guile> You get the idea: you have at your disposal all the 'mixvm' and 'gmixvm' commands by means of 'mix-' functions. But, in case you are wondering, this is only the beginning. You also have at your disposal a whole Scheme interpreter, and you can, for instance, define new functions combining the 'mix-' and all other Scheme primitives. In the next sections, you'll find examples of how to take advantage of the Guile interpreter. 3.4.2 Additional MIX Scheme functions ------------------------------------- The 'mix-' function counterparts of the 'mixvm' commands don't return any value, and are evaluated only for their side-effects (possibly including informational messages to the standard output and/or error stream). When writing your own Scheme functions to manipulate the MIX virtual machine within 'mixguile' (*note Defining new functions::), you'll probably need Scheme functions returning the value of the registers, memory cells and so on. Don't worry: 'mixguile' also offers you such functions. For instance, to access the (numerical) value of a register you can use 'mix-reg': guile> (mix-reg 'I2) 0 guile> Note that, unlike '(mix-preg 'I2)', the expression '(mix-reg 'I2)' in the above example evaluates to a Scheme number and does not produce any side-effect: guile> (number? (mix-reg 'I2)) #t guile> (number? (mix-preg 'I2)) rI2: + 00 00 (0000) #f guile> In a similar fashion, you can access the memory contents using '(mix-cell)', or the program counter using '(mix-loc)': guile> (mix-cell 3000) 786957541 guile> (mix-loc) 3002 guile> Other functions returning the contents of the virtual machine components are 'mix-cmp' and 'mix-over', which eval to the value of the comparison flag and the overflow toggle respectively. For a complete list of these additional functions, *Note mixguile::. In the next section, we'll see a sample of using these functions to extend 'mixguile''s functionality. 3.4.3 Defining new functions ---------------------------- Scheme is a powerful language, and you can use it inside 'mixguile' to easily extend the MIX interpreter's capabilities. For example, you can easily define a function that loads a file, prints its name, executes it and, finally, shows the registers contents, all in one shot: guile> (define my-load-and-run (lambda (file) (mix-load file) (display "File loaded: ") (mix-pprog) (mix-run) (mix-preg))) guile> and use it to run your programs: guile> (my-load-and-run "hello") Program loaded. Start address: 3000 File loaded: hello.mix Running ... MIXAL HELLO WORLD ... done Elapsed time: 11 /Total program time: 11 (Total uptime: 33) rA: + 00 00 00 00 00 (0000000000) rX: + 00 00 00 00 00 (0000000000) rJ: + 00 00 (0000) rI1: + 00 00 (0000) rI2: + 00 00 (0000) rI3: + 00 00 (0000) rI4: + 00 00 (0000) rI5: + 00 00 (0000) rI6: + 00 00 (0000) guile> Or, maybe, you want a function which sets a breakpoint at a specified line number before executing it: guile> (define my-load-and-run-with-bp (lambda (file line) (mix-load file) (mix-sbp line) (mix-run))) guile> (my-load-and-run-with-bp "samples/primes" 10) Program loaded. Start address: 3000 Breakpoint set at line 10 Running ... ... stopped: breakpoint at line 10 (address 3001) Elapsed time: 1 /Total program time: 1 (Total uptime: 45) guile> As a third example, the following function loads a program, runs it and prints the contents of the memory between the program's start and end addresses: guile> (define my-run (lambda (file) (mix-load file) (let ((start (mix-loc))) (mix-run) (mix-pmem start (mix-loc))))) guile> (my-run "hello") Program loaded. Start address: 3000 Running ... MIXAL HELLO WORLD ... done Elapsed time: 11 /Total program time: 11 (Total uptime: 11) 3000: + 46 58 00 19 37 (0786957541) 3001: + 00 00 00 02 05 (0000000133) 3002: + 14 09 27 01 13 (0237350989) guile> As you can see, the possibilities are virtually unlimited. Of course, you don't need to type a function definition each time you start 'mixguile'. You can write it in a file, and load it using Scheme's 'load' function. For instance, you can create a file named, say, 'functions.scm' with your definitions (or any Scheme expression) and load it at the 'mixguile' prompt: guile> (load "functions.scm") Alternatively, you can make 'mixguile' to load it for you. When 'mixguile' starts, it looks for a file named 'mixguile.scm' in your MDK configuration directory ('~/.mdk') and, if it exists, loads it before entering the REPL. Therefore, you can copy your definitions in that file, or load the 'functions.scm' file in 'mixguile.scm'. 3.4.4 Hook functions -------------------- Hooks are functions called before or after a given event occurs. In 'mixguile', you can define command and break hooks, which are associated, respectively, with command execution and program interruption events. The following sections give you a tutorial on using hook functions within 'mixguile'. 3.4.4.1 Command hooks ..................... In the previous section, we have seen how to extend 'mixguile''s functionality through the use of user defined functions. Frequently, you'll write new functions that improve in some way the workings of a built-in 'mixvm' command, following this pattern: a. Prepare the command execution b. Execute the desired command c. Perform post execution operations We call the functions executed in step (a) "pre-hook"s, and those of step "post-hook"s of the given command. 'mixguile' lets you specify pre- and post-hooks for any 'mixvm' command using the 'mix-add-pre-hook' and 'mix-add-post-hook' functions, which take as arguments a symbol naming the command and a function to be executed before (resp. after) the command. In other words, 'mixguile' will execute for you steps (a) and (c) above whenever you eval (b). The hook functions must take a single argument, which is a string list of the command's arguments. As an example, let us define the following hooks for the 'next' command: (define next-pre-hook (lambda (arglist) (mix-slog #f))) (define next-post-hook (lambda (arglist) (display "Stopped at line ") (display (mix-src-line-no)) (display ": ") (display (mix-src-line)) (newline) (mix-slog #t))) In these functions, we are using the function 'mix-slog' to turn off the informational messages produced by the virtual machine, since we are providing our own ones in the post hook function. To install these hooks, we would write: (mix-add-pre-hook 'next next-pre-hook) (mix-add-post-hook 'next next-post-hook) Assuming we have put the above expressions in 'mixguile''s initialisation file, we would obtain the following results when evaluating 'mix-next': guile> (mix-next) MIXAL HELLO WORLD Stopped at line 6: HLT guile> As a second, more elaborate, example, let's define hooks which print the address and contents of a cell being modified using 'smem'. The hook functions could be something like this: (define smem-pre-hook (lambda (arglist) (if (eq? (length arglist) 2) (begin (display "Changing address ") (display (car arglist)) (newline) (display "Old contents: ") (display (mix-cell (string->number (car arglist)))) (newline)) (error "Wrong arguments" arglist)))) (define smem-post-hook (lambda (arglist) (if (eq? (length arglist) 2) (begin (display "New contents: ") (display (mix-cell (string->number (car arglist)))) (newline))))) and we can install them using (mix-add-pre-hook 'smem smem-pre-hook) (mix-add-post-hook 'smem smem-post-hook) Afterwards, a sample execution of 'mix-smem' would look like this: guile> (mix-smem 2000 100) Changing address 2000 Old contents: 0 New contents: 100 guile> You can add any number of hooks to a given command. They will be executed in the same order as they are registered. You can also define global post (pre) hooks, which will be called before (after) any 'mixvm' command is executed. Global hook functions must admit two arguments, namely, a string naming the invoked command and a string list of its arguments, and they are installed using the Scheme functions 'mix-add-global-pre-hook' and 'mix-add-global-post-hook'. A simple example of global hook would be: guile> (define pre-hook (lambda (cmd args) (display cmd) (display " invoked with arguments ") (display args) (newline))) guile> (mix-add-global-pre-hook pre-hook) ok guile> (mix-pmem 120 125) pmem invoked with arguments (120-125) 0120: + 00 00 00 00 00 (0000000000) 0121: + 00 00 00 00 00 (0000000000) 0122: + 00 00 00 00 00 (0000000000) 0123: + 00 00 00 00 00 (0000000000) 0124: + 00 00 00 00 00 (0000000000) 0125: + 00 00 00 00 00 (0000000000) guile> Note that if you invoke 'mixvm' commands within a global hook, its associated command hooks will be run. Thus, if you have installed both the 'next' hooks described earlier and the global hook above, executing 'mix-next' will yield the following result: guile> (mix-next 5) next invoked with arguments (5) slog invoked with arguments (off) MIXAL HELLO WORLD Stopped at line 7: MSG ALF "MIXAL" slog invoked with arguments (on) guile> Adventurous readers may see the above global hook as the beginning of a command log utility or a macro recorder that saves your commands for replay. 3.4.4.2 Break hooks ................... We have seen in the previous section how to associate hooks to command execution, but they are not the whole story. You can also associate hook functions to program interruption, that is, specify functions that should be called every time the execution of a MIX program is stopped due to the presence of a breakpoint, either explicit or conditional. Break hooks take as arguments the line number and memory address at which the break occurred. A simple hook that logs the line and address of the breakpoint could be defined as: (define break-hook (lambda (line address) (display "Breakpoint encountered at line ") (display line) (display " and address ") (display address) (newline))) and installed for explicit and conditional breakpoints using (mix-add-break-hook break-hook) (mix-add-cond-break-hook break-hook) after that, every time the virtual machine encounters a breakpoint, 'break-code' shall be evaluated for you(1) (*note Break hooks-Footnote-1::). (1) You may have noticed that break hooks can be implemented in terms of command hooks associated to 'mix-run' and 'mix-next'. As a matter of fact, they _are_ implemented this way: take a look at the file '_install_dir_/share/mdk/mix-vm-stat.scm' if you are curious. 3.4.5 Scheme scripts -------------------- Another useful way of using 'mixguile' is writing executable scripts that perform a set of commands for you. This is done using the 'mixguile' switch '-s' (being a Guile shell, 'mixguile' accepts all the command options of 'guile'; type 'mixguile -h' for a list of all available command options). For instance, if you have a very useful MIX program 'foo.mix' which you want to run often, you don't have to fire up a MIX virtual machine, load and run it every time; you can write a Scheme script instead: #! /usr/bin/mixguile -s !# ;;; runprimes: execute the primes.mix program ;; load the file you want to run (mix-load "../samples/primes") ;; execute it (mix-run) ;; print the contents of registers (mix-pall) ;; ... Just save the above script to a file named, say, 'runtest', make it executable ('chmod +x runtest'), and, well, execute it from the Unix shell: $ ./runtest Program loaded. Start address: 3000 Running ... ... done Elapsed time: 190908 /Total program time: 190908 (Total uptime: 190908) rA: + 30 30 30 30 30 (0511305630) rX: + 30 30 32 32 39 (0511313959) rJ: + 47 18 (3026) rI1: + 00 00 (0000) rI2: + 55 51 (3571) rI3: + 00 19 (0019) rI4: + 31 51 (2035) rI5: + 00 00 (0000) rI6: + 00 00 (0000) Overflow: F Cmp: L $ Note that this is far more flexible that running programs non-interactively using 'mixvm' (*note Non-interactive mode::), for you can execute any combination of commands you want from a Scheme script (not just running and dumping the registers). For additional 'mixguile' command line options, see *note Invoking mixguile::. 3.5 Using Scheme in 'mixvm' and 'gmixvm' ======================================== In the previous section (*note Using mixguile::) we have seen how the Guile shell 'mixguile' offers you the possibility of using Scheme to manipulate a MIX virtual machine and extend the set of commands offered by 'mixvm' and 'gmixvm'. This possibility is not limited to the 'mixguile' shell. Actually, both 'mixvm' and 'gmixvm' incorporate an embedded Guile interpreter, and can evaluate Scheme expressions. To evaluate a single-line expression at the 'mixvm' or 'gmixvm' command prompt, simply write it and press return (the command parser will recognise it as a Scheme expression because it is parenthesized, and will pass it to the Guile interpreter). A sample 'mixvm' session using Scheme expressions could be: MIX > load hello Program loaded. Start address: 3000 MIX > (define a (mix-loc)) MIX > run Running ... MIXAL HELLO WORLD ... done Elapsed time: 11 /Total program time: 11 (Total uptime: 11) MIX > (mix-pmem a) 3000: + 46 58 00 19 37 (0786957541) MIX > (mix-pmem (mix-loc)) 3002: + 14 09 27 01 13 (0237350989) MIX > You can also load and evaluate a file, using the 'scmf' command like this: MIX> scmf /path/to/file/file.scm Therefore, you have at your disposal all the 'mixguile' goodies described above (new functions, new command definitions, hooks...) inside 'mixvm' and 'gmixvm'. In other words, these programs are extensible using Scheme. See *note Using mixguile:: for examples of how to do it. 4 Emacs tools ************* Everyone writing code knows how important a good editor is. Most systems already come with Emacs, and excellent programmer's editor. MDK adds support to Emacs for both writing and debugging MIX programs. A major mode for MIXAL source files eases edition of your code, while integration with Emacs' debugging interface (GUD) lets you use 'mixvm' without leaving your favourite text editor. This chapter shows how to use the Elisp modules included in MDK, assuming that you have followed the installation instructions in *Note Emacs support::. 4.1 MIXAL mode ============== The module 'mixal-mode.el' provides a new mode, mixal-mode, for editing MIXAL source files(1) (*note MIXAL mode-Footnote-1::). When everything is installed correctly, Emacs will select it as the major mode for editing files with extension '.mixal'. You can also activate mixal-mode in any buffer issuing the Emacs command 'M-x mixal-mode'. (1) mixal-mode has been developed and documented by Pieter E. J. Pareit 4.1.1 Basics ------------ The mode for editing mixal source files is inherited from fundamental-mode, meaning that all your favorite editing operations will still work. If you want a short introduction to Emacs, type 'C-h t' inside Emacs to start the tutorial. Mixal mode adds font locking. If you do not have font locking globally enabled, you can turn it on for mixal-mode by placing the following line in your '.emacs' file: (add-hook 'mixal-mode-hook 'turn-on-font-lock) You can also customize the colors used to colour your mixal code by changing the requisite faces. This is the list of faces used by mixal-mode: * FONT-LOCK-COMMENT-FACE Face to use for comments. * MIXAL-FONT-LOCK-LABEL-FACE Face to use for label names. * MIXAL-FONT-LOCK-OPERATION-CODE-FACE Face to use for operation code names. * MIXAL-FONT-LOCK-ASSEMBLY-PSEUDOINSTRUCTION-FACE Face to use for assembly pseudo-instruction names. 4.1.2 Help system ----------------- When coding your program, you will be thinking, looking up documentation and editing files. Emacs already helps you with editing files, but Emacs can do much more. In particular, looking up documentation is one of its strong points. Besides the info system (which you are probably already using), mixal-mode defines commands for getting particular information about a MIX operation code. With 'M-x mixal-describe-operation-code' (or its keyboard shortcut 'C-h o') you will get the documentation about a particular MIX operation code. Keep in mind that these are not assembly (MIXAL) pseudoinstructions. When the 'point' is around a MIXAL pseudoinstruction in your source file, Emacs will recognize it and will suggest the right MIX operation code. 4.1.3 Compiling and running --------------------------- After you have written your MIXAL program, you'll probably want to test it. This can be done with the MIX virtual machine. First you will need to compile your code into MIX byte code. This can be done within Emacs with the command 'M-x compile' ('C-c c'). In case of compilation errors, you can jump to the offending source code line with 'M-x next-error'. Once the program compiles without errors, you can debug or run it. To invoke the debugger, use 'M-x mixal-debug' ('C-c d'). Emacs will open a 'GUD' buffer where you can use the debugging commands described in *Note mixvm::. If you just want to execute the program, you can do so with 'M-x mixal-run' ('C-c r'). This will invoke mixvm, execute the program and show its output in a separate buffer. 4.2 GUD integration =================== If you are an Emacs user and write your MIXAL programs using this editor, you will find the elisp program 'mixvm.el' quite useful(1) (*note GUD integration-Footnote-1::). 'mixvm.el' allows running the MIX virtual machine 'mixvm' (*note mixvm::) inside an Emacs GUD buffer, while visiting the MIXAL source file in another buffer. After installing 'mixvm.el' (*note Emacs support::), you can initiate an MDK/GUD session inside Emacs with the command M-x mixvm and you will have a 'mixvm' prompt inside a newly created GUD buffer. GUD will reflect the current line in the corresponding source file buffer. (1) 'mixvm.el' has been kindly contributed by Philip E. King. 'mixvm.el' is based on a study of gdb, perldb, and pdb as found in 'gud.el', and 'rubydb3x.el' distributed with the source code to the Ruby language. 5 'mixasm', the MIXAL assembler ******************************* MIX programs, as executed by 'mixvm', are composed of binary instructions loaded into the virtual machine memory as MIX words. Although you could write your MIX programs directly as a series of words in binary format, you have at your disposal a more friendly assembly language, MIXAL (*note MIXAL::) which is compiled into binary form by 'mixasm', the MIXAL assembler included in MDK. In this chapter, you will find a complete description of 'mixasm' options. 5.1 Invoking 'mixasm' ===================== In its simplest form, 'mixasm' is invoked with a single argument, which is the name of the MIXAL file to be compiled, e.g. mixasm hello will compile either 'hello' or 'hello.mixal', producing a binary file named 'hello.mix' if no errors are found. In addition, 'mixasm' can be invoked with the following command line options (note, that, following GNU's conventions, we provide a long option name for each available single letter switch): mixasm [-vhulO] [-o OUTPUT_FILE] [--version] [--help] [--usage] [--ndebug] [--output=OUTPUT_FILE] [--list[=LIST_FILE]] file The meaning of these options is as follows: -- User Option: -v -- User Option: --version Prints version and copyleft information and exits. -- User Option: -h -- User Option: --help -- User Option: -u -- User Option: --usage Prints a summary of available options and exits. -- User Option: -O -- User Option: --ndebug Do not include debugging information in the compiled file, saving space but disallowing breakpoint setting at source level and symbol table inspection under 'mixvm'. -- User Option: -o output_file -- User Option: --output=output_file By default, the given source file FILE.MIXAL is compiled into FILE.MIX. You can provide a different name for the output file using this option. -- User Option: -l -- User Option: --list[=list_file] This option causes 'mixasm' to produce, in addition to the '.mix' file, an ASCII file containing a summary of the compilation results. The file is named after the MIXAL source file, changing its extension to '.mls' if no argument is provided; otherwise, the listing file is named according to the argument. 6 'mixvm', the MIX computer simulator ************************************* This chapter describes 'mixvm', the MIX computer simulator. 'mixvm' is a command line interface programme which simulates the MIX computer (*note The MIX computer::). It is able to run MIXAL programs (*note MIXAL::) previously compiled with the MIX assembler (*note mixasm::). The simulator allows inspection of the MIX computer components (registers, memory cells, comparison flag and overflow toggle), step by step execution of MIX programmes, and breakpoint setting to aid you in debugging your code. For a tutorial description of 'mixvm' usage, *Note Running the program::. 6.1 Invoking 'mixvm' ==================== 'mixvm' can be invoked with the following command line options (note that, following GNU's conventions, we provide a long option name for each available single letter switch): mixvm [-vhurdtq] [--version] [--help] [--usage] [--run] [--dump] [--time] [--noinit] [FILE[.mix]] The meaning of these options is as follows: -- User Option: -v -- User Option: --version Prints version and copyleft information and exits. -- User Option: -h -- User Option: --help -- User Option: -u -- User Option: --usage Prints a summary of available options and exits. -- User Option: -r -- User Option: --run Loads the specified FILE and executes it. After the program execution, 'mixvm' exits. FILE must be the name of a binary '.mix' program compiled with 'mixasm'. If your program does not produce any output, use the '-d' flag (see below) to peek at the virtual machine's state after execution. -- User Option: -d -- User Option: --dump This option must be used in conjunction with '-r', and tells 'mixvm' to print the value of the virtual machine's registers, comparison flag and overflow toggle after executing the program named FILE. See *Note Non-interactive mode::, for sample usage. -- User Option: -t -- User Option: --time This option must be used in conjunction with '-r', and tells 'mixvm' to print virtual time statistics for the program's execution. When run without the '-r' flag, 'mixvm' enters its interactive mode, showing you a prompt like this one: MIX > and waiting for your commands (*note Commands::). If the optional FILE argument is given, the file 'FILE.mix' will be loaded into the virtual machine memory before entering the interactive mode. The first time 'mixvm' is invoked, a directory named '.mdk' is created in your home directory. It contains the 'mixvm' configuration file, the command history file and (by default) the block devices files (*note Devices::). Before showing you the command prompt, 'mixvm' looks in the '~/.mdk' directory for a file named 'mixguile.scm'; if it exists, it is read and evaluated by the embedded Guile interpreter (*note Defining new functions::). You can use the '-q' command line option to skip this file loading: -- User Option: -q -- User Option: --noinit Do not load the Guile initialisation file '~/.mdk/mixguile.scm' at startup. 6.2 Interactive commands ======================== You can enter the interactive mode of the MIX virtual machine by simply invoking 'mixvm' without arguments. You will then be greeted by a shell prompt(1) (*note Commands-Footnote-1::) MIX > which indicates that a new virtual machine has been initialised and is ready to execute your commands. As we have already mentioned, this command prompt offers you command line editing facilities which are described in the Readline user's manual (chances are that you are already familiar with these command line editing capabilities, as they are present in many GNU utilities, e.g. the 'bash' shell)(2) (*note Commands-Footnote-2::). In a nutshell, readline provides command completion using the 'TAB' key and command history using the cursor keys. A history file containing the last commands typed in previous sessions is stored in the MDK configuration directory ('~/.mdk'). As a beginner, your best friend will be the 'help' command, which shows you a summary of all available MIX commands and their usage; its syntax is as follows: -- 'mixvm' command: help [command] Prints a short description of the given COMMAND and its usage. If COMMAND is omitted, 'help' prints the short description for all available commands. (1) The default command prompt, 'MIX > ', can be changed using the 'prompt' command (*note Configuration commands::) (2) The readline functionality will be available if you have compiled MDK with readline support, i.e., if GNU readline is installed in your system. This is often the case in GNU/Linux and BSD systems 6.2.1 File commands ------------------- You have at your disposal a series of commands that let you load and execute MIX executable files, as well as manipulate MIXAL source files: -- file command: load file[.mix] This command loads a binary file, FILE.MIX into the virtual machine memory, and positions the program counter at the beginning of the loaded program. This address is indicated in the MIXAL source file as the operand of the 'END' pseudoinstruction. Thus, if your 'sample.mixal' source file contains the line: END 3000 and you compile it with 'mixasm' to produce the binary file 'sample.mix', you will load it into the virtual machine as follows: MIX > load sample Program loaded. Start address: 3000 MIX > -- file command: run [file[.mix]] When executed without argument, this command initiates or resumes execution of instructions from the current program counter address. Therefore, issuing this command after a successful 'load', will run the loaded program until either a 'HLT' instruction or a breakpoint is found. If you provide a MIX filename as argument, the given file will be loaded (as with 'load' FILE) and executed. If 'run' is invoked again after program execution completion (i.e., after the 'HLT' instruction has been found in a previous run), the program counter is repositioned and execution starts again from the beginning (as a matter of fact, a 'load' command preserving the currently set breakpoints is issued before resuming execution). -- file command: edit [file[.mixal]] The source file FILE.MIXAL is edited using the editor defined in the environment variable MDK_EDITOR. If this variable is not set, the following ones are tried out in order: X_EDITOR, EDITOR and VISUAL. If invoked without argument, the source file for the currently loaded MIX file is edited. The command used to edit source files can also be configured using the 'sedit' command (*note Configuration commands::). -- file command: compile file[.mixal] The source file FILE.MIXAL is compiled (with debug information enabled) using 'mixasm'. If invoked without argument, the source file for the currently loaded MIX file is recompiled. The compilation command can be set using the 'sasm' command (*note Configuration commands::). -- file command: pprog -- file command: psrc Print the path of the currently loaded MIX program and its source file: MIX > load ../samples/primes Program loaded. Start address: 3000 MIX > pprog ../samples/primes.mix MIX > psrc /home/jao/projects/mdk/gnu/samples/primes.mixal MIx> Finally, you can use the 'quit' command to exit 'mixvm': -- file command: quit Exit 'mixvm', saving the current configuration parameters in '~/.mdk/mixvm.config'. 6.2.2 Debug commands -------------------- Sequential execution of loaded programs can be interrupted using the following debug commands: -- debug command: next [ins_number] This command causes the virtual machine to fetch and execute up to INS_NUMBER instructions, beginning from the current program counter position. Execution is interrupted either when the specified number of instructions have been fetched or a breakpoint is found, whatever happens first. If run without arguments, one instruction is executed. If 'next' is invoked again after program execution completion (i.e., after the 'HLT' instruction has been found in a previous run), the program counter is repositioned and execution starts again from the beginning (as a matter of fact, a 'load' command preserving the currently set breakpoints is issued before resuming execution). -- debug command: sbp line_number -- debug command: cbp line_no Sets a breakpoint at the specified source file line number. If the line specified corresponds to a command or to a MIXAL pseudoinstruction which does not produce a MIX instruction in the binary file (such as 'ORIG' or 'EQU') the breakpoint is set at the first source code line giving rise to a MIX instruction after the specified one. Thus, for our sample 'hello.mixal' file: * (1) * hello.mixal: say 'hello world' in MIXAL (2) * (3) * label ins operand comment (4) TERM EQU 19 the MIX console device number (5) ORIG 1000 start address (6) START OUT MSG(TERM) output data at address MSG (7) ... trying to set a breakpoint at line 5, will produce the following result: MIX > sbp 5 Breakpoint set at line 7 MIX > since line 7 is the first one compiled into a MIX instruction (at address 3000). The command 'cbp' clears a (previously set) breakpoint at the given source file line. -- debug command: spba address -- debug command: cbpa address Sets a breakpoint at the given memory ADDRESS. The argument must be a valid MIX memory address, i.e., it must belong into the range [0-3999]. Note that no check is performed to verify that the specified address is reachable during program execution. No debug information is needed to set a breakpoint by address with 'sbpa'. The command 'cbpa' clears a (previously set) breakpoint at the given memory address. -- debug command: sbpr A | X | J | Ii -- debug command: cbpr A | X | J | Ii Sets a conditional breakpoint on the specified register change. For instance, sbpr I1 will cause an interruption during program execution whenever the contents of register 'I1' changes. A previously set breakpoint is cleared using the 'cbpr' command. -- debug command: sbpm address -- debug command: cbpm address Sets a conditional breakpoint on the specified memory cell change. The argument must be a valid MIX memory address, i.e., it must belong into the range [0-3999]. For instance, sbpm 1000 will cause an interruption during program execution whenever the contents of the memory cell number 1000 changes. A previously set breakpoint is cleared using the 'cbpm' command. -- debug command: sbpo -- debug command: cbpo Sets/clears a conditional breakpoint on overflow toggle change. -- debug command: sbpc -- debug command: cbpc Sets/clears a conditional breakpoint on comparison flag change. -- debug command: cabp Clears all currently set breakpoints. -- debug command: psym [symbol_name] MIXAL programs can define symbolic constants, using either the 'EQU' pseudoinstruction or a label at the beginning of a line. Thus, in the program fragment VAR EQU 2168 ORIG 4000 START LDA VAR the symbol 'VAR' stands for the value 2168, while 'START' is assigned the value 4000. The symbol table can be consulted from the 'mixvm' command line using 'psym' followed by the name of the symbol whose contents you are interested in. When run without arguments, 'psym' will print all defined symbols and their values. The virtual machine can also show you the instructions it is executing, using the following commands: -- debug command: strace [on|off] 'strace on' enables instruction tracing. When tracing is enabled, each time the virtual machine executes an instruction (due to your issuing a 'run' or 'next' command), it is printed in its canonical form (that is, with all expressions evaluated to their numerical values) and, if the program was compiled with debug information, as it was originally typed in the MIXAL source file. Instruction tracing is disabled with 'strace off' command. A typical tracing session could be like this: MIX > strace on MIX > next 3000: [OUT 3002,0(2:3)] START OUT MSG(TERM) MIXAL HELLO WORLD Elapsed time: 1 /Total program time: 1 (Total uptime: 1) MIX > next 3001: [HLT 0,0] HLT End of program reached at address 3002 Elapsed time: 10 /Total program time: 11 (Total uptime: 11) MIX > strace off MIX > The executed instruction, as it was translated, is shown between square brackets after the memory address, and, following it, you can see the actual MIXAL code that was compiled into the executed instruction. The tracing behaviour is stored as a configuration parameter in '~/.mdk'. -- debug command: pline [LINE_NUMBER] Prints the requested source line (or the current one if LINE_NUMBER is omitted: MIX > load ../samples/hello Program loaded. Start address: 3000 MIX > pline Line 5: START OUT MSG(TERM) MIX > pline 6 Line 6: HLT MIX > -- debug command: sbt [NUMBER] This command changes the limit for the backtrace of executed instructions. If the number is omitted, the command prints the current limit. If you use a 0, backtraces are turned off. This can improve performance. If you wish for all the instructions to be logged, a -1 will enable that. The amount of memory required for unlimited backtraces can be substantial for long-running programs. -- debug command: pbt [INS_NUMBER] This command prints a backtrace of executed instructions. Its optional argument INS_NUMBER is the number of instructions to print. If it is omitted or equals zero, all executed instructions are printed. For instance, if you compile and load the following program ('bt.mixal'): ORIG 0 BEG JMP *+1 JMP *+1 FOO JMP BAR BAR HLT END BEG you could get the following traces: MIX > load bt Program loaded. Start address: 0 MIX > next MIX > pbt #0 BEG in bt.mixal:2 MIX > next MIX > pbt #0 1 in bt.mixal:3 #1 BEG in bt.mixal:2 MIX > run Running ... ... done MIX > pbt 3 #0 BAR in bt.mixal:5 #1 FOO in bt.mixal:4 #2 1 in bt.mixal:3 MIX > pbt #0 BAR in bt.mixal:5 #1 FOO in bt.mixal:4 #2 1 in bt.mixal:3 #3 BEG in bt.mixal:2 MIX > Note that the executed instruction trace gives you the label of the executed line or, if it has no label, its address. As you have probably observed, 'mixvm' prints timing statistics when running programs. This behaviour can be controlled using the 'stime' command (*note Configuration commands::). 'mixvm' is also able of evaluating w-expressions (*note W-expressions::) using the following command: -- debug command: weval WEXP Evaluates the given w-expression, WEXP. The w-expression can contain any currently defined symbol. For instance: MIX > psym START + 00 00 00 46 56 (0000003000) MIX > weval START(0:1),START(3:4) + 56 00 46 56 00 (0939716096) MIX > New symbols can be defined using the 'ssym' command: -- debug command: ssym SYM WEXP Defines the symbol named SYM with the value resulting from evaluating WEXP, a w-expression. The newly defined symbol can be used in subsequent 'weval' commands, as part of the expression to be evaluated. E.g., MIX > ssym S 2+23*START + 00 00 18 19 56 (0000075000) MIX > psym S + 00 00 18 19 56 (0000075000) MIX > weval S(3:4) + 00 00 19 56 00 (0000081408) MIX > Finally, if you want to discover which is the decimal value of a MIX word expressed as five bytes plus sign, you can use -- debug command: w2d WORD Computes the decimal value of the given word. WORD must be expressed as a sign (+/-) followed by five space-delimited, two-digit decimal values representing the five bytes composing the word. The reverse operation (showing the word representation of a decimal value) can be accomplished with 'weval'. For instance: MIX > w2d - 01 00 00 02 02 -16777346 MIX > weval -16777346 - 01 00 00 02 02 (0016777346) MIX > 6.2.3 State commands -------------------- Inspection and modification of the virtual machine state (memory, registers, overflow toggle and comparison flag contents) is accomplished using the following commands: -- state command: pstat This commands prints the current virtual machine state, which can be one of the following: - No program loaded - Program successfully loaded - Execution stopped ('next' executed) - Execution stopped: breakpoint encountered - Execution stopped: conditional breakpoint encountered - Program successfully terminated -- state command: pc Prints the current value of the program counter, which stores the address of the next instruction to be executed in a non-halted program. -- state command: sreg A | X | J | I[1-6] value -- state command: preg [A | X | J | I[1-6]] -- state command: pall 'preg' prints the contents of a given MIX register. For instance, 'preg' A will print the contents of the A-register. When invoked without arguments, all registers shall be printed: MIX > preg rA: - 00 00 00 00 35 (0000000035) rX: + 00 00 00 15 40 (0000001000) rJ: + 00 00 (0000) rI1: + 00 00 (0000) rI2: + 00 00 (0000) rI3: + 00 00 (0000) rI4: + 00 00 (0000) rI5: + 00 00 (0000) rI6: + 00 00 (0000) MIX > As you can see in the above sample, the contents are printed as the sign plus the values of the MIX bytes stored in the register and, between parenthesis, the decimal representation of its module. 'pall' prints the contents of all registers plus the comparison flag and overflow toggle. Finally, 'sreg' Sets the contents of the given register to VALUE, expressed as a decimal constant. If VALUE exceeds the maximum value storable in the given register, 'VALUE mod MAXIMUM_VALUE' is stored, e.g. MIX > sreg I1 1000 MIX > preg I1 rI1: + 15 40 (1000) MIX > sreg I1 1000000 MIX > preg I1 rI1: + 09 00 (0576) MIX > -- state command: pflags -- state command: scmp E | G | L -- state command: sover F | T 'pflags' prints the value of the comparison flag and overflow toggle of the virtual machine, e.g. MIX > pflags Overflow: F Cmp: E MIX > The values of the overflow toggle are either F (false) or T (true), and, for the comparison flag, E, G, L (equal, greater, lesser). 'scmp' and 'sover' are setters of the comparison flag and overflow toggle values. -- state command: pmem from[-to] -- state command: smem address value 'pmem' prints the contents of memory cells in the address range [FROM-TO]. If the upper limit TO is omitted, only the contents of the memory cell with address FROM is printed, as in MIX > pmem 3000 3000: + 46 58 00 19 37 (0786957541) MIX > The memory contents are displayed both as the set of five MIX bytes plus sign composing the stored MIX word and, between parenthesis, the decimal representation of the module of the stored value. 'smem' sets the content of the memory cell with address ADDRESS to VALUE, expressed as a decimal constant. 6.2.4 Configuration commands ---------------------------- This section describes commands that allow you to configure the virtual machine behaviour. This configuration is stored in the MDK directory '~/.mdk'. As you can see in their description, some commands print, as a side effect, informational messages to the standard output (e.g. 'load' prints a message telling you the loaded program's start address): these messages can be enabled/disabled using 'slog': -- config command: slog on|off Turns on/off the logging of informational messages. Note that error messages are always displayed, as well as state messages required using commands prefixed with 'p' ('preg', 'pmem' and the like). -- config command: stime on|off -- config command: ptime The 'stime' command (un)sets the printing of timing statistics, and 'ptime' prints their current value: MIX > ptime Elapsed time: 10 /Total program time: 11 (Total uptime: 11) MIX > -- config command: sedit TEMPLATE -- config command: pedit 'sedit' sets the command to be used to edit MIXAL source files with the 'edit' command. TEMPLATE must contain the control characters '%s' to mark the place where the source's file name will be inserted. For instance, if you type MIX > sedit emacsclient %s MIX > issuing the 'mixvm' command 'edit foo.mixal' will invoke the operating system command 'emacsclient foo.mixal'. 'pedit' prints the current value of the edit command template. -- config command: sasm TEMPLATE -- config command: pasm 'sasm' sets the command to be used to compile MIXAL source files with the 'compile' command. TEMPLATE must contain the control characters '%s' to mark the place where the source's file name will be inserted. For instance, if you type MIX > sasm mixasm -l %s MIX > issuing the 'mixvm' command 'compile foo.mixal' will invoke the operating system command 'mixasm -l foo.mixal'. 'pasm' prints the current value of the compile command template. -- config command: sddir DIRNAME -- config command: pddir MIX devices (*note Devices::) are implemented as regular files stored, by default, inside '~/.mdk'. The 'sddir' command lets you specify an alternative location for storing these device files, while 'pddir' prints the current device directory. Finally, you can change the default command prompt, 'MIX > ', using the 'prompt' command: -- config command: prompt PROMPT Changes the command prompt to PROMPT. If you want to include white space(s) at the end of the new prompt, bracket PROMPT using double quotes (e.g., 'prompt ">> "'). 6.2.5 Scheme commands --------------------- If you have compiled MDK with 'libguile' support (*note Special configure flags::), 'mixvm' will start and initialise an embedded Guile Scheme interpreter when it is invoked. That means that you have at your disposal, at 'mixvm''s command prompt, all the Scheme primitives described in *note Using mixguile:: and *note mixguile::, as well as any other function or hook that you have defined in the initialisation file '~/.mdk/mixguile.scm'. To evaluate a Scheme function, simply type it at the 'mixvm' command prompt (see *note Using Scheme in mixvm and gmixvm:: for a sample). Compared to the 'mixguile' program, this has only one limitation: the expressions used in 'mixvm' cannot span more than one line. You can get over this inconvenience writing your multiline Scheme expressions in a file and loading it using the 'scmf' command: -- scheme command: scmf FILE_NAME Loads the given Scheme file and evaluates it using the embedded Guile interpreter. 6.3 MIX block devices ===================== The MIX computer comes equipped with a set of block devices for input-output operations (*note Input-output operators::). 'mixvm' implements these block devices as disk files, with the exception of block device no. 19 (typewriter terminal) which is redirected to standard input/output. When you request an output operation on any other (output) device, a file named according to the following table will be created, and the specified MIX words will be written to the file in binary form (for binary devices) or in ASCII (for char devices). Files corresponding to input block devices should be created and filled beforehand to be used by the MIX virtual machine (for input-output devices this creation can be accomplished by a MIXAL program writing to the device the required data, or, if you prefer, with your favourite editor). The device files are stored, by default, in the directory '~/.mdk'; this location can be changed using the 'mixvm' command 'devdir' (*note Configuration commands::). _Device_ _No._ _filename_ _type and block size_ Tape 0-7 'tape[0-7].dev' bin i/o - 100 words Disks 8-15 'disk[0-7].dev' bin i/o - 100 words Card reader 16 'cardrd.dev' char in - 16 words Card writer 17 'cardwr.dev' char out - 16 words Line printer 18 'printer.dev' char out - 24 words Terminal 19 'stdin/stdout' char i/o - 14 words Paper tape 20 'paper.dev' char in - 14 words Devices of type char are stored as ASCII files, using one line per block. For instance, since the card reader has blocks of size 16, that is, 80 characters, it will be emulated by an ASCII file consisting of lines with length 80. If the reader finds a line with less than the required number of characters, it pads the memory with zeroes (MIX character 'space') to complete the block size. Note that the virtual machine automatically converts between the MIX and ASCII character encodings, so that you can manipulate char device files with any ASCII editor. In addition, the reader is not case-sensitive, i.e., it automatically converts lowercase letters to their uppercase counterparts (since the MIX character set does not include the former). The typewriter (device no. 19) lets you use the standard input and output in your MIXAL programs. For instance, here is a simple 'echo' program: * simple echo program TERM EQU 19 the typewriter device BUF EQU 500 input buffer ORIG 1000 START IN BUF(TERM) read a block (70 chars) OUT BUF(TERM) write the read chars HLT END START Input lines longer than 70 characters (14 words) are trimmed. On the other hand, if you type less than a block of characters, whitespace (MIX character zero) is used as padding. 7 'gmixvm', the GTK virtual machine *********************************** This chapter describes the graphical MIX virtual machine emulator shipped with MDK. In addition to having all the command-oriented functionalities of the other virtual machines ('mixvm' and 'mixguile'), 'gmixvm' offers you a graphical interface displaying the status of the virtual machine, the source code of the the downloaded programs and the contents of the MIX devices. 7.1 Invoking 'gmixvm' ===================== If you have built MDK with GTK+ support (*note Installing MDK::), a graphical front-end for the MIX virtual machine will be available in your system. You can invoke it by typing gmixvm [-vhuq] [--version] [--help] [--usage] [--noinit] at your command prompt, where the options have the following meanings: -- User Option: -v -- User Option: --version Prints version and copyleft information and exits. -- User Option: -h -- User Option: --help -- User Option: -u -- User Option: --usage Prints a summary of available options and exits. -- User Option: -q -- User Option: --noinit Do not load the Guile initialisation file '~/.mdk/mixguile.scm' at startup. This file contains any local Scheme code to be executed by the embedded Guile interpreter at startup (*note Using Scheme in mixvm and gmixvm::). Typing 'gmixvm' or 'gmixvm -q' at your command prompt, the main window will appear, offering you a graphical interface to run and debug your MIX programs. |-----------------------------------------------------------| | Menu | |-----------------------------------------------------------| | | | | | | | | | MIXVM / MIXAL / Devices | | | | | | | | | | | | | |-----------------------------------------------------------| | | | Command output | | | | | | | |-----------------------------------------------------------| | Command prompt | |-----------------------------------------------------------| | Status bar | |-----------------------------------------------------------| Apart from the menu and status bars, we can distinguish two zones (or halves) in this main window. In the upper half of 'gmixvm''s main window there is a notebook with three pages, namely, * a MIX virtual machine view, which shows you the registers, flags, memory contents and time statistics of the virtual machine; * a MIXAL source view, which shows the MIXAL file and lets you manage breakpoints; * a Devices view, which shows you the output to character based MIX block devices. These three windows can be detached from the notebook, using either the penultimate toolbar button (which detachs the currently visible notebook page) or the menu entries under 'View->Detached windows'. On the other hand, the main window's lower half presents you a 'mixvm' command prompt and a logging area where results of the issued commands are presented. These widgets implement a 'mixvm' console which offers almost the same functionality as its CLI counterpart. When 'gmixvm' is run, it creates a directory named '.mdk' in your home directory (if it does not already exist). The '.mdk' directory contains the program settings, the device files used by your MIX programs (*note Devices::), and a command history file. The following sections describe the above mentioned components of 'gmixvm'. 7.2 MIXVM console ================= In the lower half of the 'gmixvm' main window, you will find a command text entry and, above it, an echo area. These widgets offer you the same functionality as its CLI counterpart, 'mixvm' (*note mixvm::). You can issue almost all 'mixmv' commands at the 'gmixvm''s command prompt in order to manipulate the MIX virtual machine. Please refer to *Note mixvm::, for a description of these commands, and to *Note Getting started::, for a tutorial on using the MIX virtual machine. The command prompt offers command line completion for partially typed commands using the key; e.g., if you type lo the command is automatically completed to 'load'. If multiple completions are available, they will be shown in the echo area. Thus, typing p will produce the following output on the echo area: Completions: pc psym preg pflags pall pmem which lists all the available commands starting with 'p'. In addition, the command prompt maintains a history of typed commands, which can be recovered using the arrow up and down keys. As mentioned above, a file containing previous sessions' commands is stored in the configuration directory '~/.mdk', and reloaded every time you start 'gmixvm'. You can change the font used to display the issued commands and the messages in the echo area using the 'Settings->Change font->Command prompt' and 'Settings->Change font->Command log' menu commands. 7.3 MIX virtual machine ======================= The first notebook's page displays the current status of the virtual machine. There you can find the registers' contents, the value of the comparison and overflow flags, the location pointer, a list with all MIX memory cells and their contents, and the time statistics (including total uptime, elapsed time since the last run command and total execution time for the currently loaded MIX program). If you click any register entry, you will be prompted for a new register's contents. In the same manner, click on any address of the memory cells list to be prompted for the new contents of the clicked cell. If you click the address column's title, a dialog asking you for a memory address will appear; if you introduce a valid address, this will be the first cell displayed in the scrollable list after you click the OK button. The register contents are shown as a list of MIX bytes plus sign. If you place the mouse pointer over any of them, the decimal value of this MIX word will appear inside a tooltip. You can change the font used to display the MIX virtual machine contents using the 'Settings->Change font->MIX' menu command. 7.4 MIXAL source view ===================== The second notebook's page, dubbed Source, shows you the MIXAL source of the currently loaded MIX file. The information is presented in four columns. The first column displays little icons showing the current program pointer and any set breakpoints. The second and third columns show the address and memory contents of the compiled MIX instruction, while the last one displays its corresponding MIXAL representation, together with the source file line number. You can set/unset breakpoints by clicking on any line that has an associated memory address. You can change the font used to display the MIXAL source code using the 'Settings->Change font->MIXAL' menu command. 7.5 MIX devices view ==================== The last notebook page, dubbed Devices, shows you the output/input to/from MIX block devices (the console, line printer, paper tape, disks, card and tapes *note Devices::) produced by the running program. Input device contents is read from files located in the '~/.mdk' directory, and the output is also written to files at the same location. Note that device tabs will appear as they are used by the MIX program being run, and that loading a new MIX program will close all previously open devices. The input/output for binary block devices (tapes and disks) is a list of MIX words, which can be displayed either in decimal or word format (e.g. - 67 or - 00 00 00 01 03). The format used by 'gmixvm' can be configured using the 'Settings->Device output' menu command for each binary device. You can change the font used to display the devices content using the 'Settings->Change font->Devices' menu command. 7.6 Menu and status bars ======================== The menu bar gives you access to the following commands: -- File: Load... Opens a file dialog that lets you specify a binary MIX file to be loaded in the virtual machine's memory. It is equivalent to the 'mixvm''s 'load' command (*note File commands::). -- File: Edit... Opens a file dialog that lets your specify a MIXAL source file to be edited. It is equivalent to the 'mixvm''s 'edit' command (*note File commands::). The program used for editing can be specified using the menu entry 'Settings->External programs', or using the 'mixvm' command 'sedit'. -- File: Compile... Opens a file dialog that lets your specify a MIXAL source file to be compiled. It is equivalent to the 'mixvm''s 'compile' command (*note File commands::). The command used for compiling can be specified using the menu entry 'Settings->External programs', or using the 'mixvm' command 'sasm'. -- File: Exit Exits the application. -- Debug: Run Runs the currently loaded MIX program, up to the next breakpoint. It is equivalent to the 'mixvm''s 'run' command (*note Debug commands::). -- Debug: Next Executes the next MIX instruction. It is equivalent to the 'mixvm''s 'next' command (*note Debug commands::). -- Debug: Clear breakpoints Clears all currently set breakpoints. It is equivalent to the 'mixvm''s 'cabp' command. -- Debug: Symbols... Opens a dialog showing the list of symbols defined in the currently loaded MIX program. The font used to display this list can be customised using the meny entry 'Settings->Change font->Symbol list'. -- View: Toolbar(s) Toggles the toolbar(s) in the 'gmixvm' window(s) (when notebook pages are detached, each one has its own toolbar). -- View: Detached windows Virtual machine -- View: Detached windows Source -- View: Detached windows Devices These toggles let you detach (or re-attach) the corresponding notebook page. -- Settings: Change font Lets you change the font used in the various 'gmixv' widgets (i.e. commad prompt, command log, Virtual machine, Source, Devices and Symbol list). There is also an entry ('All') to change all fonts at once. -- Settings: Device output... Opens a dialog that lets you specify which format shall be used to show the contents of MIX binary block devices. The available formats are decimal (e.g. -1234) and MIX word (e.g. - 00 00 00 19 18). -- Settings: Devices dir... Opens a dialog that lets you choose where the MIX device files will be stored ('~/.mdk' is the default location). You can also specify the devices directory using the 'mixvm' command 'sddir' (*note Configuration commands::). -- Settings: External programs... This menu command opens a dialog that lets you specify the commands used for editing and compiling MIXAL source files. The commands are specified as template strings, where the control substring '%s' will be substituted by the actual file name. Thus, if you want to edit programs using 'vi' running in an 'xterm', you must enter the command template 'xterm -e vi %s' in the corresponding dialog entry. These settings can also be changed using the 'mixvm' commands 'sedit' and 'sasm' (*note Configuration commands::). -- Settings: Save Saves the current settings. -- Settings: Save on exit Mark this checkbox if you want 'gmixvm' to save its settings every time you quit the program. -- Help: About... Shows information about 'gmixvm''s version and copyright. On the other hand, the status bar displays the name of the last loaded MIX file. In addition, when the mouse pointer is over a MIXAL source file line that contains symbols, a list of these symbols with their values will appear in the status bar. 8 'mixguile', the Scheme virtual machine **************************************** This chapter provides a reference to using 'mixguile' and the Scheme function library giving access to the MIX virtual machine in the MDK emulators ('mixguile', 'mixvm' and 'gmixvm'). See *note Using mixguile:: for a tutorial, step by step introduction to 'mixguile' and using Scheme as an extension language for the MDK MIX virtual machines. 8.1 Invoking 'mixguile' ======================= Invoking 'mixguile' without arguments will enter the Guile REPL (read-eval-print loop) after loading, if it exists, the user's initialisation file ('~/.mdk/mixguile.scm'). 'mixguile' accepts the same command line options than Guile: mixguile [-s SCRIPT] [-c EXPR] [-l FILE] [-e FUNCTION] [-qhv] [--help] [--version] The meaning of these options is as follows: -- User Option: -h -- User Option: --help Prints usage summary and exits. -- User Option: -v -- User Option: --version Prints version and copyleft information and exits. -- User Option: -s SCRIPT Loads Scheme code from SCRIPT, evaluates it and exits. This option can be used to write executable Scheme scripts, as described in *note Scheme scripts::. -- User Option: -c EXPR Evaluates the given Scheme expression and exits. -- User Option: -l FILE Loads the given Scheme file and enters the REPL (read-eval-print loop). -- User Option: -e FUNCTION After reading the script, executes the given function using the provided command line arguments. For instance, you can write the following Scheme script: #! /usr/bin/mixguile \ -e main -s !# ;;; execute a given program and print the registers. (define main (lambda (args) ;; load the file provided as a command line argument (mix-load (cadr args)) ;; execute it (mix-run) ;; print the contents of registers (mix-pall))) save it in a file called, say, 'foo', make it executable, and run it as $ ./foo hello This invocation will cause the evaluation of the 'main' function with a list of command line parameters as its argument ('("./foo" "hello")' in the above example. Note that command line options to mixguile must be written in their own line after the '\' symbol. -- User Option: -q Do not load user's initialisation file. When 'mixguile' starts up, it looks for a file named 'mixguile.scm' in the user's MDK configuration directory ('~/.mdk'), and loads it if it exists. This option tells 'mixguile' to skip this initialisation file loading. 8.2 Scheme functions reference ============================== As we have previously pointed out, 'mixguile' embeds a MIX virtual machine that can be accessed through a set of Scheme functions, that is, of a Scheme library. Conversely, 'mixvm' and 'gmixvm' contain a Guile interpreter, and are able to use this same Scheme library, as well as all the other Guile/Scheme primitives and any user defined function. Therefore, you have at your disposal a powerful programming language, Scheme, to extend the MDK virtual machine emulators (see *note Using Scheme in mixvm and gmixvm:: for samples of how to do it). The following subsections describe available functions the MIX/Scheme library. 8.2.1 'mixvm' command wrappers ------------------------------ For each of the 'mixvm' commands listed in *note Commands::, there is a corresponding Scheme function named by prefixing the command name with 'mix-' (e.g., 'mix-load', 'mix-run' and so on). These command wrappers are implemented using a generic command dispatching function: -- Function: mixvm-cmd command argument Dispatches the given COMMAND to the MIX virtual machine appending the provided ARGUMENT. Both COMMAND and 'argument' must be strings. The net result is as writing "COMMAND ARGUMENT" at the 'mixvm' or 'gmixvm' command prompt. For instance, you can invoke the 'run' command at the 'mixvm' prompt in three equivalent ways: MIX > run hello MIX > (mix-run "hello") MIX > (mixvm-cmd "run" "hello") (only the two last forms can be used at the 'mixguile' prompt or inside a Scheme script). The 'mix-' functions evaluate to a unspecified value. If you want to check the result of the last 'mixvm' command invocation, use the 'mix-last-result' function: -- Function: mix-last-result Returns #T if the last 'mixvm' command invocation was successful, #F otherwise. Using this function, we could improve the script for running a program presented in the previous section by adding error checking: #! /usr/bin/mixguile \ -e main -s !# ;;; Execute a given program and print the registers. (define main (lambda (args) ;; load the file provided as a command line argument (mix-load (cadr args)) ;; execute it if mix-load succeeded (if (mix-last-result) (mix-run)) ;; print the contents of registers if the above commands succeeded (if (mix-last-result) (mix-pall)))) Please, refer to *note Commands:: for a list of available commands. Given the description of a 'mixvm', it is straightforward to use its Scheme counterpart and, therefore, we shall not give a complete description of these functions here. Instead, we will only mention those wrappers that exhibit a treatment of their differing from that of their command counterpart. -- Function: mix-preg [register] -- Function: mix-sreg register value The argument REGISTER of these functions can be either a string or a symbol representing the desired register. For instance, the following invocations are equivalent: (mix-preg 'I1) (mix-preg "I1") -- Function: mix-pmem from [to] The command 'pmem' takes a single argument which can be either a cell number or a range of the form 'FROM-TO'. This function takes one argument to ask for a single memory cell contents, or two parameters to ask for a range. For instance, the following commands are equivalent: MIX > pmem 10-12 0010: + 00 00 00 00 00 (0000000000) 0011: + 00 00 00 00 00 (0000000000) 0012: + 00 00 00 00 00 (0000000000) MIX > (mix-pmem 10 12) 0010: + 00 00 00 00 00 (0000000000) 0011: + 00 00 00 00 00 (0000000000) 0012: + 00 00 00 00 00 (0000000000) MIX > -- Function: mix-sover #t|#f The command 'sover' takes as argument either the string 'T' or the string 'F', to set, respectively, the overflow toggle to true or false. Its Scheme counterpart, 'mix-sover', takes as argument a Scheme boolean value: '#t' (true) or '#f'. For the remaining functions, you simply must take into account that when the command arguments are numerical, the corresponding Scheme function takes as arguments Scheme number literals. On the other hand, when the command argument is a string, the argument of its associated Scheme function will be a Scheme string. By way of example, the following invocations are pairwise equivalent: MIX > load ../samples/hello MIX > (mix-load "../samples/hello") MIX > next 5 MIX > (mix-next 5) 8.2.2 Hook functions -------------------- Hooks are functions evaluated before or after executing a 'mixvm' command (or its corresponding Scheme function wrapper), or after an explicit or conditional breakpoint is found during the execution of a MIX program. The following functions let you install hooks: -- Function: mix-add-pre-hook command hook Adds a function to the list of pre-hooks associated with the given COMMAND. COMMAND is a string naming the corresponding 'mixvm' command, and HOOK is a function which takes a single argument: a string list of the commands arguments. The following scheme code defines a simple hook and associates it with the 'run' command: (define run-hook (lambda (args) (display "argument list: ") (display args) (newline))) (mix-add-pre-hook "run" run-hook) Pre-hooks are executed, in the order they are added, before invoking the corresponding command (or its associated Scheme wrapper function). -- Function: mix-add-post-hook command hook Adds a function to the list of pre-hooks associated with the given COMMAND. The arguments have the same meaning as in 'mix-add-pre-hook'. -- Function: mix-add-global-pre-hook hook -- Function: mix-add-global-post-hook hook Global pre/post hooks are executed before/after any 'mixvm' command or function wrapper invocation. In this case, HOOK takes two arguments: a string with the name of the command being invoked, and a string list with its arguments. -- Function: mix-add-break-hook hook -- Function: mix-add-cond-break hook Add a hook funtion to be executed when an explicit (resp. conditional) breakpoint is encountered during program execution. HOOK is a function taking two arguments: the source line number where the hook has occurred, and the current program counter value. The following code shows a simple definition and installation of a break hook: (define break-hook (lambda (line address) (display "Breakpoint at line ") (display line) (display " and address ") (display address) (newline))) (mix-add-break-hook break-hook) Break hook functions are entirely implemented in Scheme using regular post-hooks for the 'next' and 'run' commands. If you are curious, you can check the Scheme source code at '_prefix_/share/mdk/mixguile-vm-stat.scm' (where _prefix_ stands for your root install directory, usually '/usr' or '/usr/local'. See *note Hook functions:: for further examples on using hook functions. 8.2.3 Additional VM functions ----------------------------- When writing non-trivial Scheme extensions using the MIX/Scheme library, you will probably need to evaluate the contents of the virtual machine components (registers, memory cells and so on). For instance, you may need to store the contents of the 'A' register in a variable. The Scheme functions described so far are of no help: you can print the contents of 'A' using '(mix-preg 'A)', but you cannot define a variable containing the contents of 'A'. To address this kind of problems, the MIX/Scheme library provides the following additional functions: -- Function: mixvm-status -- Function: mix-vm-status Return the current status of the virtual machine, as a number ('mixvm-status') or as a symbol ('mix-vm-status'). Possible return values are: '(mixvm-status)' '(mix-vm-status)' 0 MIX_ERROR Loading or execution error 1 MIX_BREAK Breakpoint encountered 2 MIX_COND_BREAK Conditional breakpoint 3 MIX_HALTED Execution terminated 4 MIX_RUNNING Execution stopped after 'next' 5 MIX_LOADED Program successfully loaded 6 MIX_EMPTY No program loaded -- Function: mix-vm-error? -- Function: mix-vm-break? -- Function: mix-vm-cond-break? -- Function: mix-vm-halted? -- Function: mix-vm-running? -- Function: mix-vm-loaded? -- Function: mix-vm-empty? Predicates asking whether the current virtual machine status is 'MIX_ERROR', 'MIX_BREAK', etc. -- Function: mix-reg register -- Function: mix-set-reg! register value 'mix-reg' evaluates to a number which is the contents of the specified REGISTER. 'mix-set-reg' sets the contents of the given REGISTER to VALUE. The register can be specified either as a string ('"A"', '"X"', etc.) or as a symbol (''A', ''X', etc.). For instance, guile> (mix-reg 'A) 2341 guile> (mix-set-reg! "A" 2000) ok guile> (define reg-a (mix-reg 'A)) guile> (display reg-a) 2000 guile> -- Function: mix-cell cell_no -- Function: mix-set-cell! cell_no value Evaluate and set the contents of the memory cell number CELL_NO. Both CELL_NO and VALUE are Scheme numbers. -- Function: mix-loc Evaluates to the value of the location counter (i.e., the address of the next instruction to be executed). -- Function: mix-over -- Function: mix-set-over! #t|#f 'mix-over' evaluates to '#t' if the overflow toggle is set, and to '#f' otherwise. The value of the overflow toggle can be modified using 'mix-set-over!'. -- Function: mix-cmp -- Function: mix-set-cmp! 'L|'E|'G Evaluate and set the comparison flag. Possible values are the scheme symbols 'L' (lesser), 'E' (equal) and 'G' (greater). -- Function: mix-up-time Evaluates to the current virtual machine uptime. -- Function: mix-lap-time Evaluates to the current virtual machine lapsed time, i.e., the time elapsed since the last 'run' or 'next' command. -- Function: mix-prog-time Evaluates to the total time spent executing the currently loaded program. -- Function: mix-prog-name Evaluates to a string containing the basename (without any leading path) of the currently loaded MIX program. -- Function: mix-prog-path Evaluates to a string containing the full path to the currently loaded MIX program. -- Function: mix-src-path Evaluates to a string containing the full path to the source file of the currently loaded MIX program. -- Function: mix-src-line [lineno] -- Function: mix-src-line-no 'mix-src-line-no' evaluates to the current source file number during the execution of a program. 'mix-src-line' evaluates to a string containing the source file line number LINENO; when invoked without argument, it evaluates to '(mix-src-line (mix-src-line-no))'. -- Function: mix-ddir Evaluates to a string containing the full path of the current device directory. 9 Reporting Bugs **************** If you have any questions, comments or suggestions, please send electronic mail to the author . If you find a bug in MDK, please send electronic mail to the MDK bug list . In your report, please include the version number, which you can find by running 'mixasm --version'. Also include in your message the output that the program produced and the output you expected. Appendix A Copying ****************** GNU MDK is distributed under the GNU General Public License (GPL) and this manual under the GNU Free Documentation License (GFDL). A.1 GNU General Public License ============================== Version 3, 29 June 2007 Copyright (C) 2007 Free Software Foundation, Inc. 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The work must carry prominent notices stating that it is released under this License and any conditions added under section 7. This requirement modifies the requirement in section 4 to "keep intact all notices". c. You must license the entire work, as a whole, under this License to anyone who comes into possession of a copy. This License will therefore apply, along with any applicable section 7 additional terms, to the whole of the work, and all its parts, regardless of how they are packaged. This License gives no permission to license the work in any other way, but it does not invalidate such permission if you have separately received it. d. If the work has interactive user interfaces, each must display Appropriate Legal Notices; however, if the Program has interactive interfaces that do not display Appropriate Legal Notices, your work need not make them do so. A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an "aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate. 6. Conveying Non-Source Forms. You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways: a. Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by the Corresponding Source fixed on a durable physical medium customarily used for software interchange. b. Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by a written offer, valid for at least three years and valid for as long as you offer spare parts or customer support for that product model, to give anyone who possesses the object code either (1) a copy of the Corresponding Source for all the software in the product that is covered by this License, on a durable physical medium customarily used for software interchange, for a price no more than your reasonable cost of physically performing this conveying of source, or (2) access to copy the Corresponding Source from a network server at no charge. c. Convey individual copies of the object code with a copy of the written offer to provide the Corresponding Source. This alternative is allowed only occasionally and noncommercially, and only if you received the object code with such an offer, in accord with subsection 6b. d. Convey the object code by offering access from a designated place (gratis or for a charge), and offer equivalent access to the Corresponding Source in the same way through the same place at no further charge. You need not require recipients to copy the Corresponding Source along with the object code. If the place to copy the object code is a network server, the Corresponding Source may be on a different server (operated by you or a third party) that supports equivalent copying facilities, provided you maintain clear directions next to the object code saying where to find the Corresponding Source. Regardless of what server hosts the Corresponding Source, you remain obligated to ensure that it is available for as long as needed to satisfy these requirements. e. Convey the object code using peer-to-peer transmission, provided you inform other peers where the object code and Corresponding Source of the work are being offered to the general public at no charge under subsection 6d. A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object code work. A "User Product" is either (1) a "consumer product", which means any tangible personal property which is normally used for personal, family, or household purposes, or (2) anything designed or sold for incorporation into a dwelling. In determining whether a product is a consumer product, doubtful cases shall be resolved in favor of coverage. 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If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not apply if neither you nor any third party retains the ability to install modified object code on the User Product (for example, the work has been installed in ROM). The requirement to provide Installation Information does not include a requirement to continue to provide support service, warranty, or updates for a work that has been modified or installed by the recipient, or for the User Product in which it has been modified or installed. Access to a network may be denied when the modification itself materially and adversely affects the operation of the network or violates the rules and protocols for communication across the network. Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying. 7. Additional Terms. "Additional permissions" are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were included in this License, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions. When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission. Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms: a. Disclaiming warranty or limiting liability differently from the terms of sections 15 and 16 of this License; or b. Requiring preservation of specified reasonable legal notices or author attributions in that material or in the Appropriate Legal Notices displayed by works containing it; or c. Prohibiting misrepresentation of the origin of that material, or requiring that modified versions of such material be marked in reasonable ways as different from the original version; or d. Limiting the use for publicity purposes of names of licensors or authors of the material; or e. Declining to grant rights under trademark law for use of some trade names, trademarks, or service marks; or f. Requiring indemnification of licensors and authors of that material by anyone who conveys the material (or modified versions of it) with contractual assumptions of liability to the recipient, for any liability that these contractual assumptions directly impose on those licensors and authors. All other non-permissive additional terms are considered "further restrictions" within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying. If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms. Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way. 8. Termination. You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11). However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation. Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice. Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10. 9. Acceptance Not Required for Having Copies. You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so. 10. Automatic Licensing of Downstream Recipients. Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License. An "entity transaction" is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts. You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it. 11. Patents. A "contributor" is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's "contributor version". A contributor's "essential patent claims" are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, "control" includes the right to grant patent sublicenses in a manner consistent with the requirements of this License. Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version. In the following three paragraphs, a "patent license" is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To "grant" such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party. If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. "Knowingly relying" means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid. If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it. A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007. Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law. 12. No Surrender of Others' Freedom. If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program. 13. Use with the GNU Affero General Public License. Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such. 14. Revised Versions of this License. The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License "or any later version" applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation. If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program. Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version. 15. Disclaimer of Warranty. THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 16. Limitation of Liability. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. 17. Interpretation of Sections 15 and 16. If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee. END OF TERMS AND CONDITIONS --------------------------- How to Apply These Terms to Your New Programs --------------------------------------------- If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES. Copyright (C) YEAR NAME OF AUTHOR This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see . Also add information on how to contact you by electronic and paper mail. If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode: PROGRAM Copyright (C) YEAR NAME OF AUTHOR This program comes with ABSOLUTELY NO WARRANTY; for details type 'show w'. This is free software, and you are welcome to redistribute it under certain conditions; type 'show c' for details. The hypothetical commands 'show w' and 'show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an "about box". You should also get your employer (if you work as a programmer) or school, if any, to sign a "copyright disclaimer" for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see . The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read . A.2 GNU Free Documentation License ================================== Version 1.2, November 2002 Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software. We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference. 1. APPLICABILITY AND DEFINITIONS This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law. A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language. A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them. The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none. The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words. A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque". Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only. The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text. A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition. The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License. 2. VERBATIM COPYING You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3. You may also lend copies, under the same conditions stated above, and you may publicly display copies. 3. COPYING IN QUANTITY If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects. If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages. If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public. It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document. 4. MODIFICATIONS You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version: A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission. B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement. C. State on the Title page the name of the publisher of the Modified Version, as the publisher. D. Preserve all the copyright notices of the Document. E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices. F. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below. G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice. H. Include an unaltered copy of this License. I. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence. J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission. K. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein. L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles. M. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version. N. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section. O. Preserve any Warranty Disclaimers. If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles. You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard. You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. 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Concept Index ************* * Menu: * .mix file: Compiling. (line 1616) * .mixal file: Writing a source file. (line 1541) * .mls file: Invoking mixasm. (line 2533) * address: MIX architecture. (line 502) * address transfer operators: Address transfer operators. (line 824) * arithmetic operators: Arithmetic operators. (line 787) * assembler: Compiling. (line 1606) * assembler <1>: mixasm. (line 2481) * assembly: MIXAL. (line 1150) * binary operator: Expressions. (line 1356) * binary programs: Compiling. (line 1606) * break hook: Break hooks. (line 2250) * breakpoints: Debugging. (line 1863) * breakpoints <1>: Debugging. (line 1882) * bugs: Problems. (line 3905) * byte: MIX architecture. (line 502) * cell: MIX architecture. (line 502) * CM: MIX architecture. (line 547) * comments: MIXAL directives. (line 1335) * comparison indicator: MIX architecture. (line 547) * comparison operators: Comparison operators. (line 877) * compiling: Compiling. (line 1606) * conversion operators: Conversion operators. (line 1023) * exection time: Execution times. (line 1116) * FDL, GNU Free Documentation License: GNU Free Documentation License. (line 4636) * field specification: MIX architecture. (line 502) * fspec: MIX architecture. (line 502) * global hook: Command hooks. (line 2203) * gmixvm: gmixvm. (line 3232) * GPL, GNU General Public License: GNU General Public License. (line 3923) * GTK+: gmixvm. (line 3232) * GUI: gmixvm. (line 3232) * help: Interactive mode. (line 1815) * hook function: Hook functions. (line 2112) * index: MIX architecture. (line 502) * input-output devices: MIX architecture. (line 547) * input-output operators: Input-output operators. (line 986) * instruction: MIX architecture. (line 502) * instruction set: MIX instruction set. (line 606) * interactive mode: Running the program. (line 1627) * interactive mode <1>: Interactive mode. (line 1728) * Introduction: Introduction. (line 160) * jump operators: Jump operators. (line 901) * literal constants: Literal constants. (line 1509) * load: Interactive mode. (line 1744) * loading operators: Loading operators. (line 686) * local symbols: Local symbols. (line 1458) * memory: MIX architecture. (line 502) * memory cell: MIX architecture. (line 502) * miscellaneous operators: Miscellaneous operators. (line 1100) * MIX: MIX and MIXAL tutorial. (line 483) * MIX architecture: MIX architecture. (line 502) * MIX assembly language: MIXAL. (line 1150) * MIX byte: MIX architecture. (line 502) * MIX computer: MIX architecture. (line 502) * MIX instruction: MIX architecture. (line 502) * MIX register: MIX architecture. (line 502) * MIX word: MIX architecture. (line 502) * MIXAL: MIX and MIXAL tutorial. (line 483) * MIXAL <1>: MIXAL. (line 1150) * MIXAL <2>: Writing a source file. (line 1541) * MIXAL <3>: mixasm. (line 2481) * mixasm: Compiling. (line 1606) * mixasm <1>: mixasm. (line 2481) * mixguile: The mixguile shell. (line 1934) * mixguile <1>: mixguile. (line 3540) * mixguile options: Invoking mixguile. (line 3549) * mixvm: Running the program. (line 1627) * mixvm <1>: mixvm. (line 2542) * next: Debugging. (line 1832) * non-interactive: Scheme scripts. (line 2282) * non-interactive mode: Running the program. (line 1627) * non-interactive mode <1>: Non-interactive mode. (line 1656) * operator: Expressions. (line 1356) * OV: MIX architecture. (line 547) * overflow toggle: MIX architecture. (line 547) * pc: Interactive mode. (line 1757) * pmem: Interactive mode. (line 1786) * post-hook: Hook functions. (line 2112) * pre-hook: Hook functions. (line 2112) * preg: Interactive mode. (line 1807) * problems: Problems. (line 3905) * psym: Debugging. (line 1903) * questions: Problems. (line 3905) * rA: MIX architecture. (line 532) * register: MIX architecture. (line 502) * register <1>: MIX architecture. (line 532) * REPL: The mixguile shell. (line 1934) * rIn: MIX architecture. (line 532) * rJ: MIX architecture. (line 532) * run: Interactive mode. (line 1761) * rX: MIX architecture. (line 532) * sbp: Debugging. (line 1882) * sbpa: Debugging. (line 1863) * Scheme: The mixguile shell. (line 1934) * Scheme functions: Defining new functions. (line 2027) * Scheme script: Scheme scripts. (line 2282) * scmf: Using Scheme in mixvm and gmixvm. (line 2331) * shift: Shift operators. (line 1056) * shift operators: Shift operators. (line 1056) * source file: Writing a source file. (line 1541) * storing operators: Storing operators. (line 750) * suggestions: Problems. (line 3905) * tail recursion: Concept Index. (line 5062) * time: Execution times. (line 1116) * tutorial: Getting started. (line 1533) * un: MIX architecture. (line 547) * unary operator: Expressions. (line 1356) * virtual machine: Compiling. (line 1606) * w-expressions: W-expressions. (line 1398) * word: MIX architecture. (line 502) Instructions and commands ************************* * Menu: * About...: Menu and status bars. (line 3529) * ADD: Arithmetic operators. (line 790) * ALF: MIXAL directives. (line 1251) * cabp: Debug commands. (line 2817) * cbp: Debug commands. (line 2744) * cbpa: Debug commands. (line 2775) * cbpc: Debug commands. (line 2814) * cbpm: Debug commands. (line 2798) * cbpo: Debug commands. (line 2810) * cbpr: Debug commands. (line 2787) * Change font: Menu and status bars. (line 3489) * CHAR: Conversion operators. (line 1030) * Clear breakpoints: Menu and status bars. (line 3468) * CMPA: Comparison operators. (line 887) * CMPi: Comparison operators. (line 891) * CMPX: Comparison operators. (line 889) * compile: File commands. (line 2698) * Compile...: Menu and status bars. (line 3449) * CON: MIXAL directives. (line 1248) * DECA: Address transfer operators. (line 848) * DECi: Address transfer operators. (line 852) * DECX: Address transfer operators. (line 850) * Detached windows: Menu and status bars. (line 3482) * Detached windows <1>: Menu and status bars. (line 3483) * Detached windows <2>: Menu and status bars. (line 3484) * Device output...: Menu and status bars. (line 3495) * Devices dir...: Menu and status bars. (line 3503) * DIV: Arithmetic operators. (line 801) * edit: File commands. (line 2689) * Edit...: Menu and status bars. (line 3442) * END: MIXAL directives. (line 1254) * ENNA: Address transfer operators. (line 835) * ENNi: Address transfer operators. (line 839) * ENNX: Address transfer operators. (line 837) * ENTA: Address transfer operators. (line 829) * ENTi: Address transfer operators. (line 833) * ENTX: Address transfer operators. (line 831) * EQU: MIXAL directives. (line 1246) * Exit: Menu and status bars. (line 3456) * External programs...: Menu and status bars. (line 3510) * help: Commands. (line 2642) * HLT: Miscellaneous operators. (line 1108) * IN: Input-output operators. (line 990) * INCA: Address transfer operators. (line 841) * INCi: Address transfer operators. (line 845) * INCX: Address transfer operators. (line 843) * IOC: Input-output operators. (line 996) * JAE: Jump operators. (line 957) * JAN: Jump operators. (line 951) * JANN: Jump operators. (line 954) * JANP: Jump operators. (line 956) * JANZ: Jump operators. (line 955) * JAO: Jump operators. (line 958) * JAP: Jump operators. (line 953) * JAZ: Jump operators. (line 952) * JBUS: Input-output operators. (line 1002) * JE: Jump operators. (line 937) * JG: Jump operators. (line 939) * JGE: Jump operators. (line 941) * JiN: Jump operators. (line 973) * JiNN: Jump operators. (line 976) * JiNP: Jump operators. (line 978) * JiNZ: Jump operators. (line 977) * JiP: Jump operators. (line 975) * JiZ: Jump operators. (line 974) * JL: Jump operators. (line 935) * JLE: Jump operators. (line 945) * JMP: Jump operators. (line 919) * JNE: Jump operators. (line 943) * JNOV: Jump operators. (line 929) * JOV: Jump operators. (line 927) * JRED: Input-output operators. (line 999) * JSJ: Jump operators. (line 921) * JXE: Jump operators. (line 968) * JXN: Jump operators. (line 962) * JXNN: Jump operators. (line 965) * JXNP: Jump operators. (line 967) * JXNZ: Jump operators. (line 966) * JXO: Jump operators. (line 969) * JXP: Jump operators. (line 964) * JXZ: Jump operators. (line 963) * LDA: Loading operators. (line 689) * LDAN: Loading operators. (line 698) * LDi: Loading operators. (line 695) * LDiN: Loading operators. (line 704) * LDX: Loading operators. (line 692) * LDXN: Loading operators. (line 701) * load: File commands. (line 2660) * Load...: Menu and status bars. (line 3437) * mix-add-break-hook: Hooks. (line 3769) * mix-add-cond-break: Hooks. (line 3770) * mix-add-global-post-hook: Hooks. (line 3763) * mix-add-global-pre-hook: Hooks. (line 3762) * mix-add-post-hook: Hooks. (line 3757) * mix-add-pre-hook: Hooks. (line 3739) * mix-cell: Additional VM functions. (line 3847) * mix-cmp: Additional VM functions. (line 3862) * mix-ddir: Additional VM functions. (line 3898) * mix-lap-time: Additional VM functions. (line 3870) * mix-last-result: mixvm wrappers. (line 3658) * mix-loc: Additional VM functions. (line 3852) * mix-over: Additional VM functions. (line 3856) * mix-pmem: mixvm wrappers. (line 3695) * mix-preg: mixvm wrappers. (line 3686) * mix-prog-name: Additional VM functions. (line 3878) * mix-prog-path: Additional VM functions. (line 3882) * mix-prog-time: Additional VM functions. (line 3874) * mix-reg: Additional VM functions. (line 3830) * mix-set-cell!: Additional VM functions. (line 3848) * mix-set-cmp!: Additional VM functions. (line 3863) * mix-set-over!: Additional VM functions. (line 3857) * mix-set-reg!: Additional VM functions. (line 3831) * mix-sover: mixvm wrappers. (line 3712) * mix-src-line: Additional VM functions. (line 3890) * mix-src-line-no: Additional VM functions. (line 3891) * mix-src-path: Additional VM functions. (line 3886) * mix-sreg: mixvm wrappers. (line 3687) * mix-up-time: Additional VM functions. (line 3867) * mix-vm-break?: Additional VM functions. (line 3821) * mix-vm-cond-break?: Additional VM functions. (line 3822) * mix-vm-empty?: Additional VM functions. (line 3826) * mix-vm-error?: Additional VM functions. (line 3820) * mix-vm-halted?: Additional VM functions. (line 3823) * mix-vm-loaded?: Additional VM functions. (line 3825) * mix-vm-running?: Additional VM functions. (line 3824) * mix-vm-status: Additional VM functions. (line 3807) * mixvm-cmd: mixvm wrappers. (line 3639) * mixvm-status: Additional VM functions. (line 3806) * MOVE: Miscellaneous operators. (line 1103) * MUL: Arithmetic operators. (line 797) * next: Debug commands. (line 2730) * Next: Menu and status bars. (line 3464) * NOP: Miscellaneous operators. (line 1106) * NUM: Conversion operators. (line 1026) * ORIG: MIXAL directives. (line 1243) * OUT: Input-output operators. (line 993) * pall: State commands. (line 3001) * pasm: Configuration commands. (line 3112) * pbt: Debug commands. (line 2886) * pc: State commands. (line 2994) * pddir: Configuration commands. (line 3128) * pedit: Configuration commands. (line 3096) * pflags: State commands. (line 3035) * pline: Debug commands. (line 2865) * pmem: State commands. (line 3051) * pprog: File commands. (line 2705) * preg: State commands. (line 3000) * prompt: Configuration commands. (line 3137) * psrc: File commands. (line 2706) * pstat: State commands. (line 2984) * psym: Debug commands. (line 2820) * ptime: Configuration commands. (line 3087) * quit: File commands. (line 2720) * run: File commands. (line 2676) * Run: Menu and status bars. (line 3459) * sasm: Configuration commands. (line 3111) * Save: Menu and status bars. (line 3522) * Save on exit: Menu and status bars. (line 3525) * sbp: Debug commands. (line 2743) * sbpc: Debug commands. (line 2813) * sbpm: Debug commands. (line 2797) * sbpo: Debug commands. (line 2809) * sbpr: Debug commands. (line 2786) * sbt: Debug commands. (line 2877) * scmf: Scheme commands. (line 3158) * scmp: State commands. (line 3036) * sddir: Configuration commands. (line 3127) * sedit: Configuration commands. (line 3095) * SLA: Shift operators. (line 1059) * SLAX: Shift operators. (line 1061) * SLB: Shift operators. (line 1072) * SLC: Shift operators. (line 1063) * slog: Configuration commands. (line 3080) * smem: State commands. (line 3052) * sover: State commands. (line 3037) * spba: Debug commands. (line 2774) * SRA: Shift operators. (line 1060) * SRAX: Shift operators. (line 1062) * SRB: Shift operators. (line 1073) * SRC: Shift operators. (line 1064) * sreg: State commands. (line 2999) * ssym: Debug commands. (line 2947) * STA: Storing operators. (line 756) * STi: Storing operators. (line 760) * stime: Configuration commands. (line 3086) * STJ: Storing operators. (line 762) * strace: Debug commands. (line 2838) * STX: Storing operators. (line 758) * STZ: Storing operators. (line 764) * SUB: Arithmetic operators. (line 793) * Symbols...: Menu and status bars. (line 3472) * Toolbar(s): Menu and status bars. (line 3478) * w2d: Debug commands. (line 2964) * weval: Debug commands. (line 2935)