\input texinfo @c -*-texinfo-*- @c %**start of header @setfilename mdk.info @settitle MIX Development Kit (mdk) @finalout @setchapternewpage odd @c %**end of header @include version.texi @set JAO Jos@'e Antonio Ortega Ruiz @footnotestyle separate @ifinfo This file documents the the @sc{mdk} utilities for developing programs using Donald Knuth's MIX language. Copyright (C) 2000, 2001 @value{JAO} Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through TeX and print the results, provided the printed document carries copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled ``Copying'' and ``GNU General Public License'' are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. @end ifinfo @titlepage @title MDK @subtitle MIX Development Kit @subtitle Edition @value{EDITION}, for @sc{mdk} Version @value{VERSION} @subtitle @value{UPDATED} @author by @value{JAO} @page @vskip 0pt plus 1filll Copyright @copyright{} 2000, 2001 @value{JAO} Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled ``Copying'' and ``GNU General Public License'' are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. @end titlepage @node Top, Introduction, (dir), (dir) @ifinfo This file documents the @sc{mdk} utilities to develop, run and debug programs written in the MIXAL programming language. MIXAL is an assembler-like language for programming a virtual computer called MIX. They were created by Donald Knuth in the first volume of @cite{The Art of Computer Programming} (Addison Wesley, 1997). @sc{mdk} was written by @value{JAO} and is released under the GNU General Public license (@pxref{Copying}), so that users are free to share and improve it. @end ifinfo @menu * Introduction:: * MIX and MIXAL tutorial:: Learn the innards of MIX and MIXAL. * Getting started:: Basic usage of the @sc{mdk} tools. * mixvm:: Invoking the MIX virtual machine. * mixasm:: Invoking the MIXAL assembler. * Copying:: @sc{mdk} licensing terms. * Problems:: Reporting bugs. * Concept Index:: Index of concepts. @detailmenu --- The Detailed Node Listing --- MIX and MIXAL tutorial * The MIX computer:: Architecture and instruction set of the MIX computer. * MIXAL:: The MIX assembly language. The MIX computer * MIX architecture:: * MIX instruction set:: MIX instruction set * Instruction structure:: * Loading operators:: * Storing operators:: * Arithmetic operators:: * Address transfer operators:: * Comparison operators:: * Jump operators:: * Input-output operators:: * Conversion operators:: * Shift operators:: * Miscellaneous operators:: * Execution times:: MIXAL * Basic structure:: Writing basic MIXAL programs. * MIXAL directives:: Assembler directives. * Expressions:: Evaluation of expressions. * W-expressions:: Evaluation of w-expressions. * Local symbols:: Special symbol table entries. * Literal constants:: Specifying an immediate operand. Getting started * Writing a source file:: A sample MIXAL source file. * Compiling:: Using @code{mixasm} to compile source files into binary format. * Running the program:: Running and debugging your program. Running the program * Non-interactive mode:: Running your programs non-interactively. * Interactive mode:: Running programs interactively. * Debugging:: Commands for debugging your programs. @code{mixvm}, the MIX computer simulator * Invocation:: Options when invoking @code{mixvm}. * Commands:: Commands available in interactive mode. * Devices:: MIX block devices implementation. Interactive commands * File commands:: Loading and executing programs. * Debug commands:: Debugging programs. * State commands:: Inspecting the virtual machine state. @code{mixasm}, the MIXAL assembler * Invoking @code{mixasm}:: @code{mixasm} options @end detailmenu @end menu @node Introduction, MIX and MIXAL tutorial, Top, Top @comment node-name, next, previous, up @unnumbered Introduction @cindex Introduction In his book series @cite{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 ilustrate 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 @sc{mdk} package aims at providing such virtual development environment on a GNU box. Thus, @sc{mdk} offers you a set of utilities to simulate the MIX computer and to write, compile, run and debug MIXAL programs. As of version @value{VERSION}, @sc{mdk} includes the following programs: @table @code @item mixvm MIX virtual machine. Emulation of the MIX computer. @item mixasm MIXAL assembler. Assembler which translates MIXAL source files into programs that can be run (and debugged) by @code{mixvm}. @end table @code{mixvm} implements 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 @code{mixasm}. This manual gives you a tutorial of MIX and MIXAL, and a thorough description of the use of the @sc{mdk} utilities. @node MIX and MIXAL tutorial, Getting started, Introduction, Top @comment node-name, next, previous, up @chapter MIX and MIXAL tutorial @cindex MIX @cindex MIXAL In the book series @cite{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. @menu * The MIX computer:: Architecture and instruction set of the MIX computer. * MIXAL:: The MIX assembly language. @end menu @node The MIX computer, MIXAL, MIX and MIXAL tutorial, MIX and MIXAL tutorial @comment node-name, next, previous, up @section The MIX computer In this section, you will find a description of the MIX computer, its components and instruction set. @menu * MIX architecture:: * MIX instruction set:: @end menu @node MIX architecture, MIX instruction set, The MIX computer, The MIX computer @comment node-name, next, previous, up @subsection MIX architecture @cindex byte @cindex MIX byte @cindex word @cindex MIX word @cindex MIX architecture @cindex MIX computer @cindex register @cindex MIX register @cindex field specification @cindex fspec @cindex instruction @cindex MIX instruction @cindex address @cindex memory cell @cindex cell @cindex memory @cindex index The basic information storage unit in the MIX computer is the @dfn{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 @emph{regular} byte. Unless otherwise stated, we shall use the word @dfn{byte} to refer to a MIX 6-bit byte. A MIX @dfn{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, @example ----------------------------------------------- | 0 | 1 | 2 | 3 | 4 | 5 | ----------------------------------------------- | +/- | byte | byte | byte | byte | byte | ----------------------------------------------- @end example @noindent Sample MIX words are @samp{- 12 00 11 01 63} and @samp{+ 12 11 34 43 00}. You can refer to subfields within a word using a @dfn{field specification} or @dfn{fspec} of the form @samp{(L:R)}, where @samp{L} denotes the first byte and @samp{R} the last byte of the subfield. When @samp{L} is zero, the subfield includes the word's sign. An fspec can also be represented as a single value @samp{F}, given by @code{F = 8*L + R} (thus the fspec @samp{(1:3)}, denoting the first three bytes of a word, is represented by the integer 11). The MIX computer stores information in @dfn{registers}, that can store either a word or two bytes and sign (see below), and @dfn{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: @cindex rA @cindex rX @cindex rJ @cindex rIn @cindex register @table @samp @item rA A register. General purpose register holding a word. Usually its contents serves as the operand of arithmetic and storing instructions. @item rX X register. General purpose register holding a word. Often it acts as an extension or a replacement of @samp{rA}. @item rJ J (jump) register. This register stores positive two-byte values, usually representing a jump address. @item rI[1-6] Index registers. These six registers can store a signed two-byte value. Their contents is used as indexing values for the computation of effective memory addresses. @end table @cindex @sc{ov} @cindex @sc{cm} @cindex @samp{Un} @cindex overflow toggle @cindex comparison indicator @cindex input-output devices @noindent In addition, the MIX computer contains: @itemize @minus @item An @dfn{overflow toggle} (a single bit with values @dfn{on} or @dfn{off}). In this manual, this toggle is denoted @sc{ov}. @item A @dfn{comparison indicator} (having three values: @dfn{EQUAL}, @dfn{GREATER} or @dfn{LESS}). In this manual, this indicator is denoted @sc{cm}, and its possible values are abbreviated as @dfn{E}, @dfn{G} and @dfn{L}. @item Input-output block devices. Each device is labelled as @samp{Un}, where @samp{n} runs from 0 to 20. In Knuth's definition, @samp{U0-7} are magnetic tape units, @samp{U8-15} are disks and drums, @samp{U16} is a card reader, @samp{U17} is a card writer, @samp{U18} is a line printer and, @samp{U19} is a typewriter terminal, and @samp{U20}, a paper tape. Our implementation maps these devices to disk files, except for @samp{U19}, which represents the standard output. @end itemize As noted above, communication of the MIX computer with the external world is achieved by a set of input-output devices which can be "connected" to it. Interchange of information is done in blocks of words whose length depend on the device at hand (see @pxref{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: @multitable {00} {C} {00} {C} {00} {C} {00} {C} @item 00 @tab @tab 01 @tab A @tab 02 @tab B @tab 03 @tab C @item 04 @tab D @tab 05 @tab E @tab 06 @tab F @tab 07 @tab G @item 08 @tab H @tab 09 @tab I @tab 10 @tab d @tab 11 @tab J @item 12 @tab K @tab 13 @tab L @tab 14 @tab M @tab 15 @tab N @item 16 @tab O @tab 17 @tab P @tab 18 @tab Q @tab 19 @tab R @item 20 @tab s @tab 21 @tab p @tab 22 @tab S @tab 23 @tab T @item 24 @tab U @tab 25 @tab V @tab 26 @tab W @tab 27 @tab X @item 28 @tab Y @tab 29 @tab Z @tab 30 @tab 0 @tab 31 @tab 1 @item 32 @tab 2 @tab 33 @tab 3 @tab 34 @tab 4 @tab 35 @tab 5 @item 36 @tab 6 @tab 37 @tab 7 @tab 38 @tab 8 @tab 39 @tab 9 @item 40 @tab . @tab 41 @tab , @tab 42 @tab ( @tab 43 @tab ) @item 44 @tab + @tab 45 @tab - @tab 46 @tab * @tab 47 @tab / @item 48 @tab = @tab 49 @tab $ @tab 50 @tab < @tab 51 @tab > @item 52 @tab @@ @tab 53 @tab ; @tab 54 @tab : @tab 55 @tab ' @end multitable @noindent The value 0 represents a whitespace. Lowercase letters (d, s, p) correspond to symbols non 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 fetchs 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 @dfn{location counter} (also known as program counter in other architectures). The next section, @xref{MIX instruction set}, gives a complete description of the available MIX binary instructions. @node MIX instruction set, , MIX architecture, The MIX computer @comment node-name, next, previous, up @subsection MIX instruction set @cindex 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 remaininig subsections are devoted to describing the actual instructions available to the MIX programmer. @menu * Instruction structure:: * Loading operators:: * Storing operators:: * Arithmetic operators:: * Address transfer operators:: * Comparison operators:: * Jump operators:: * Input-output operators:: * Conversion operators:: * Shift operators:: * Miscellaneous operators:: * Execution times:: @end menu @node Instruction structure, Loading operators, MIX instruction set, MIX instruction set @comment node-name, next, previous, up @subsubsection Instruction structure MIX @dfn{instructions} are codified as words with the following subfield structure: @multitable @columnfractions .15 .20 .65 @item @emph{Subfield} @tab @emph{fspec} @tab @emph{Description} @item ADDRESS @tab (0:2) @tab The first two bytes plus sign are the @dfn{address} field. Combined with the INDEX field, denotes the memory address to be used by the instruction. @item INDEX @tab (3:3) @tab The third byte is the @dfn{index}, normally used for indexing the address@footnote{The actual memory address the instruction refers to, is obtained by adding to ADDRESS the value of the @samp{rI} register denoted by INDEX.}. @item MOD @tab (4:4) @tab Byte four is used either as an operation code modifier or as a field specification. @item OPCODE @tab (5:5) @tab The last (least significant) byte in the word denotes the operation code. @end multitable @noindent or, graphically, @example ------------------------------------------------ | 0 | 1 | 2 | 3 | 4 | 5 | ------------------------------------------------ | ADDRESS | INDEX | MOD | OPCODE | ------------------------------------------------ @end example For a given instruction, @samp{M} stands for the memory address obtained after indexing the ADDRESS subfield (using its INDEX byte), and @samp{V} is the contents of the subfield indicated by MOD of the memory cell with address @samp{M}. For instance, suppose that we have the following contents of MIX registers and memory cells: @example [rI2] = + 00 63 [31] = - 10 11 00 11 22 @end example @noindent where @samp{[n]} denotes the contents of the nth memory cell and @samp{[rI2]} the contents of register @samp{rI2}@footnote{In general, @samp{[X]} will denote the contents of entity @samp{X}; thus, by definition, @w{@samp{V = [M](MOD)}}.}. Let us consider the binary instruction @w{@samp{I = - 00 32 02 11 10}}. For this instruction we have: @example 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 @end example In the following subsections, we will assing to each MIX instruction a mnemonic, or symbolic name. For instance, the mnemonic of @samp{OPCODE} 10 is @samp{LD2}. Thus we can rewrite the above instruction as @example LD2 -32,2(1:3) @end example @noindent or, for a generic instruction: @example MNEMONIC ADDRESS,INDEX(MOD) @end example @noindent 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). @node Loading operators, Storing operators, Instruction structure, MIX instruction set @comment node-name, next, previous, up @subsubsection Loading operators @cindex loading operators The following instructions are used to load memory contents into a register. @ftable @code @item LDA Put in rA the contents of cell no. M. OPCODE = 8, MOD = fspec. @code{rA <- V}. @item LDX Put in rX the contents of cell no. M. OPCODE = 15, MOD = fspec. @code{rX <- V}. @item LDi Put in rIi the contents of cell no. M. OPCODE = 8 + i, MOD = fspec. @code{rIi <- V}. @item LDAN Put in rA the negative contents of cell no. M. OPCODE = 16, MOD = fspec. @code{rA <- -V}. @item LDXN Put in rX the negative contents of cell no. M. OPCODE = 23, MOD = fspec. @code{rX <- -V}. @item LDiN Put in rIi the negative contents of cell no. M. OPCODE = 16 + i, MOD = fspec. @code{rIi <- -V}. @end ftable In all the above load instructions the @samp{MOD} field selects the bytes of the memory cell with address @samp{M} which are loaded into the requisite register (indicated by the @samp{OPCODE}). For instance, the word @w{@samp{+ 00 13 01 27 11}} represents the instruction @example LD3 13,1(3:3) ^ ^ ^ ^ | | | | | | | --- MOD = 27 = 3*8 + 7 | | --- INDEX = 1 | --- ADDRESS = 00 13 --- OPCODE = 11 @end example Let us suppose that, prior to this instruction execution, the state of the MIX computer is the following: @example [rI1] = - 00 01 [rI3] = + 24 12 [12] = - 01 02 03 04 05 @end example @noindent As, in this case, @w{@samp{M = 13 + [rI1] = 12}}, we have @w{@samp{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 @example [rI1] = - 00 01 [rI3] = + 00 03 [12] = - 01 02 03 04 05 @end example To further illustrate loading operators, the following table shows the contents of @samp{rX} after different @samp{LDX} instructions: @table @samp @item LDX 12(0:0) [rX] = - 00 00 00 00 00 @item LDX 12(0:1) [rX] = - 00 00 00 00 01 @item LDX 12(3:5) [rX] = + 00 00 03 04 05 @item LDX 12(3:4) [rX] = + 00 00 00 03 04 @item LDX 12(0:5) [rX] = - 01 02 03 04 05 @end table @node Storing operators, Arithmetic operators, Loading operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Storing operators @cindex 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. @ftable @code @item STA Store rA. OPCODE = 24, MOD = fspec. @code{V <- rA}. @item STX Store rX. OPCODE = 31, MOD = fspec. @code{V <- rX}. @item STi Store rIi. OPCODE = 24 + i, MOD = fspec. @code{V <- rIi}. @item STJ Store rJ. OPCODE = 32, MOD = fspec. @code{V <- rJ}. @item STZ Store zero. OPCODE = 33, MOD = fspec. @code{V <- 0}. @end ftable By way of example, consider the instruction @samp{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 @emph{the memory address}). The others bytes of the memory cell retain their values. Thus, if prior to the instruction execution we have @example [1200] = - 20 21 22 23 24 [rA] = + 01 02 03 04 05 @end example @noindent we will end up with @example [1200] = - 20 04 05 23 24 [rA] = + 01 02 03 04 05 @end example As a second example, @samp{ST2 1000(0)} will set the sign of @samp{[1000]} to that of @samp{[rI2]}. @node Arithmetic operators, Address transfer operators, Storing operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Arithmetic operators @cindex arithmetic operators The following instructions perform arithmetic operations between rA and rX register and memory contents. @ftable @code @item ADD Add and set OV if overflow. OPCODE = 1, MOD = fspec. @w{@code{rA <- rA +V}}. @item SUB Sub and set OV if overflow. OPCODE = 2, MOD = fspec. @w{@code{rA <- rA - V}}. @item MUL Multiply V times rA and store the 10-bytes product in rAX. OPCODE = 3, MOD = fspec. @w{@code{rAX <- rA x V}}. @item DIV rAX is considered a 10-bytes number, and it is divided by V. OPCODE = 4, MOD = fspec. @w{@code{rA <- rAX / V}}, @code{rX} <- reminder. @end ftable In all the above instructions, @samp{[rA]} is one of the operands of the binary arithmetic operation, the other being @samp{V} (that is, the specified subfield of the memory cell with address @samp{M}), padded with zero bytes on its left-side to complete a word. In multiplication and division, the register @samp{X} comes into play as a right-extension of the register @samp{A}, so that we are able to handle 10-byte numbers whose more significant bytes are those of @samp{rA} (the sign of this 10-byte number is that of @samp{rA}: @samp{rX}'s sign is ignored). Addition and substraction 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 @w{1,073,741,823} (the maximum value storable in a MIX word) is stored in @samp{rA}, and the overflow toggle is set to TRUE. @node Address transfer operators, Comparison operators, Arithmetic operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Address transfer operators @cindex address transfer operators In these instructions, @samp{M} (the address of the instruction after indexing) is used as a number instead of as the address of a memory cell. @ftable @code @item ENTA Enter [rA]. OPCODE = 48, MOD = 2. @code{rA <- M}. @item ENTX Enter [rX]. OPCODE = 55, MOD = 2. @code{rX <- M}. @item ENTi Enter [rIi]. OPCODE = 48 + i, MOD = 2. @code{rIi <- M}. @item ENNA Enter negative [rA]. OPCODE = 48, MOD = 3. @code{rA <- -M}. @item ENNX Enter negative [rX]. OPCODE = 55, MOD = 3. @code{rX <- -M}. @item ENNi Enter negative [rIi]. OPCODE = 48 + i, MOD = 3. @code{rIi <- -M}. @item INCA Increase [rA]. OPCODE = 48, MOD = 0. @code{rA <- rA + M}. @item INCX Increase [rX]. OPCODE = 55, MOD = 0. @code{rX <- rX + M}. @item INCi Increase [rIi]. OPCODE = 48 + i, MOD = 0. @code{rIi <- rIi + M}. @item DECA Decrease [rA]. OPCODE = 48, MOD = 1. @code{rA <- rA - M}. @item DECX Decrease [rX]. OPCODE = 55, MOD = 0. @code{rX <- rX - M}. @item DECi Decrease [rIi]. OPCODE = 48 + i, MOD = 0. @code{rIi <- rIi - M}. @end ftable In the above instructions, the subfield @samp{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 @samp{rA} the value -2000 (- 00 00 00 31 16), you can use the binary instruction @w{+ 31 16 00 03 48}, or, symbolically, @example ENNA 2000 @end example @noindent Used in conjuction with the store operations (@samp{STA}, @samp{STX}, etc.), these instructions also allow you to set memory cells contents to concrete values. Note that in these address transfer operators, the @samp{MOD} field is not a subfield specificator, but serves to define (together with @samp{OPCODE}) the concrete operation to be performed. @node Comparison operators, Jump operators, Address transfer operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Comparison operators @cindex 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 @samp{V}, and set the @sc{cm} indicator to the result of the comparison (i.e. to @samp{E}, @samp{G} or @samp{L}, equal, greater or lesser respectively). @ftable @code @item CMPA Compare [rA] with V. OPCODE = 56, MOD = fspec. @item CMPX Compare [rX] with V. OPCODE = 63, MOD = fspec. @item CMPi Compare [rIi] with V. OPCODE = 56 + i, MOD = fspec. @end ftable 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. @node Jump operators, Input-output operators, Comparison operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Jump operators @cindex jump operators The MIX computer has an internal register, called the @dfn{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, the 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 @samp{rJ} (except for @code{JSJ}), and the location counter is set to the value of @samp{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 @samp{rJ}. The MIX computer provides the following jump instructions: With these instructions you force a jump to the specified address. Use @samp{JSJ} if you do not care about the return address. @ftable @code @item JMP Unconditional jump. OPCODE = 39, MOD = 0. @item JSJ Unconditional jump, but rJ is not modified. OPCODE = 39, MOD = 1. @end ftable These instructions check the overflow toggle to decide whether to jump or not. @ftable @code @item JOV Jump if OV is set (and turn it off). OPCODE = 39, MOD = 2. @item JNOV Jump if OV is not set (and turn it off). OPCODE = 39, MOD = 3. @end ftable In the following instructions, the jump is conditioned to the contents of the comparison flag: @ftable @code @item JL Jump if @w{@code{[CM] = L}}. OPCODE = 39, MOD = 4. @itemx JE Jump if @w{@code{[CM] = E}}. OPCODE = 39, MOD = 5. @itemx JG Jump if @w{@code{[CM] = G}}. OPCODE = 39, MOD = 6. @itemx JGE Jump if @code{[CM]} does not equal @code{L}. OPCODE = 39, MOD = 7. @itemx JNE Jump if @code{[CM]} does not equal @code{E}. OPCODE = 39, MOD = 8. @itemx JLE Jump if @code{[CM]} does not equal @code{G}. OPCODE = 39, MOD = 9. @end ftable You can also jump conditioned to the value stored in the MIX registers, using the following instructions: @ftable @code @item JAN @itemx JAZ @itemx JAP @itemx JANN @itemx JANZ @itemx JANP Jump if the contents of rA is, respectively, negative, zero, positive, non-negative, non-zero or non-positive. OPCODE = 40, MOD = 0, 1, 2, 3, 4, 5. @item JXN @itemx JXZ @itemx JXP @itemx JXNN @itemx JXNZ @itemx JXNP Jump if the contents of rX is, respectively, negative, zero, positive, non-negative, non-zero or non-positive. OPCODE = 47, MOD = 0, 1, 2, 3, 4, 5. @item JiN @itemx JiZ @itemx JiP @itemx JiNN @itemx JiNZ @itemx JiNP Jump if the contents of rIi is, respectively, negative, zero, positive, non-negative, non-zero or non-positive. OPCODE = 40 + i, MOD = 0, 1, 2, 3, 4, 5. @end ftable @node Input-output operators, Conversion operators, Jump operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Input-output operators @cindex input-output operators As explained in previous sections (@pxref{MIX architecture}), the MIX computer can interact with a series of block devices. To that end, you have at your disposal the following instructions: @ftable @code @item IN Transfer a block of words from the specified unit to memory, starting at address M. OPCODE = 36, MOD = I/O unit. @item OUT Transfer a block of words from memory (starting at address M) to the specified unit. OPCODE = 37, MOD = I/O unit. @item IOC Perfom a control operation (given by M) on the specified unit. OPCODE = 35, MOD = I/O unit. @item JRED Jump to M if the specified unit is ready. OPCODE = 38, MOD = I/O unit. @item JBUS Jump to M if the specified unit is busy. OPCODE = 34, MOD = I/O unit. @end ftable @noindent In all the above instructions, the @samp{MOD} subfile must be in the range 0-20, since it denotes the operation's target device. The @samp{IOC} instruction only makes sense for tape devices (@samp{MOD} = 0-7 or 20): it shifts the read/write pointer by the number of words given by @samp{M} (if it equals zero, the tape is rewound)@footnote{In Knuth's original definition, there are other control operations available, but they do not make sense when implementing the block devices as disk files (as we do in @sc{mdk} simulator). For the same reason, @sc{mdk} devices are always ready, since all input-output operations are performed using synchronous system calls.}. @node Conversion operators, Shift operators, Input-output operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Conversion operators @cindex conversion operators The following instructions convert between numerical values and their character representations. @ftable @code @item 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. @item CHAR Convert the number stored in rA to a character representation and store it in rAX. OPCODE = 5, MOD = 1. @end ftable @noindent Digits are represented in MIX by the range of values 30-39 (digits 9-0). Thus, if the contents of @samp{rA} and @samp{rX} is, for instance, @example [rA] = + 30 30 31 32 33 [rX] = + 31 35 39 30 34 @end example @noindent the represented number is 0012315904, and @samp{NUM} will store this value in @samp{rA} (i.e., we end up with @samp{[rA]} = @w{+ 0 46 62 52 0} = 12315904. @samp{CHAR} performs the inverse operation. @node Shift operators, Miscellaneous operators, Conversion operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Shift operators @cindex shift @cindex shift operators The following instructions perform byte-wise shifts of the contents of @samp{rA} and @samp{rX}. @ftable @code @item SLA @itemx SRA @itemx SLAX @itemx SRAX @itemx SLC @itemx SRC Shift rA or rAX left, right, or rAX circularly left or right. M specifies the number of bytes to be shifted. OPCODE = 6, MOD = 0, 1, 2, 3, 4, 5. @end ftable @noindent If we begin with, say, @samp{[rA]} = @w{- 01 02 03 04 05}, we would have the following modifications to @samp{rA} contents when performing the instructions on the left column: @multitable {SLA 00} {[rA] = - 00 00 00 00 00} @item SLA 2 @tab [rA] = - 03 04 05 00 00 @item SRA 1 @tab [rA] = - 00 01 02 03 04 @item SLC 3 @tab [rA] = - 04 05 01 02 03 @item SRC 24 @tab [rA] = - 05 01 02 03 04 @end multitable @noindent Note that the sign is unaffected by shift operations. On the other hand, @samp{SLAX} and @samp{SRAX} treat @samp{rA} and @samp{rX} as a single 10-bytes register (ignoring again the signs), so that, if we begin with @samp{[rA]} = @w{+ 01 02 03 04 05} and @samp{[rX]} = @w{- 06 07 08 09 10}, executing @samp{SLAX 3} would yield: @example [rA] = + 04 05 06 07 08 [rX] = - 09 10 00 00 00 @end example @node Miscellaneous operators, Execution times, Shift operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Miscellaneous operators @cindex miscellaneous operators Finally, we list in the following table three miscellaneous MIX instructions which do not fit in any of the previous subsections: @ftable @code @item MOVE Move MOD words from M to the location stored in rI1. OPCODE = 7, MOD = no. of bytes. @item NOP No operation. OPCODE = 0, MOD = 0. @item HLT Halt. Stops instruction fetching. OPCODE = 5, MOD = 2. @end ftable @noindent The only effect of executing @samp{NOP} is increasing the location counter, while @samp{HLT} usually marks program termination. @node Execution times, , Miscellaneous operators, MIX instruction set @comment node-name, next, previous, up @subsubsection Execution times @cindex exection time @cindex time When writing MIXAL programs (or any kind of programs, for that matter), whe shall often be interested in their execution time. Loosely speaking, we will interested in the answer to the question: how long takes 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 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. @multitable {INSSSS} {01} {INSSSS} {01} {INSSSS} {01} {INSSSS} {01} @item @code{NOP} @tab 1 @tab @code{ADD} @tab 2 @tab @code{SUB} @tab 2 @tab @code{MUL} @tab 10 @item @code{DIV} @tab 12 @tab @code{NUM} @tab 10 @tab @code{CHAR} @tab 10 @tab @code{HLT} @tab 10 @item @code{SLx} @tab 2 @tab @code{SRx} @tab 2 @tab @code{LDx} @tab 2 @tab @code{STx} @tab 2 @item @code{JBUS} @tab 1 @tab @code{IOC} @tab 1 @tab @code{IN} @tab 1@tab @code{OUT} @tab 1 @item @code{JRED} @tab 1 @tab @code{Jx} @tab 1 @tab @code{INCx} @tab 1 @tab @code{DECx} @tab 1 @item @code{ENTx} @tab 1 @tab @code{ENNx} @tab 1 @tab @code{CMPx} @tab 1 @tab @code{MOVE} @tab 1+F @end multitable In the above table, 'F' stands for the number of blocks to be moved (given by the @code{FSPEC} subfield of the instruction); @code{SLx} and @code{SRx} are a short cut for the byte-shifting operations; @code{LDx} denote all the loading operations; @code{STx} are the storing operations; @code{Jx} stands for all the jump operations, and so on with the rest of abbreviations. @node MIXAL, , The MIX computer, MIX and MIXAL tutorial @comment node-name, next, previous, up @section MIXAL @cindex MIXAL @cindex MIX assembly language @cindex assembly 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 @sc{mdk} are described later on (@pxref{Getting started}). @menu * Basic structure:: Writing basic MIXAL programs. * MIXAL directives:: Assembler directives. * Expressions:: Evaluation of expressions. * W-expressions:: Evaluation of w-expressions. * Local symbols:: Special symbol table entries. * Literal constants:: Specifying an immediate operand. @end menu @node Basic structure, MIXAL directives, MIXAL, MIXAL @comment node-name, next, previous, up @subsection 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@footnote{We shall call them, collectively, MIXAL instructions.} are written in MIXAL (one per source file line) according to the following pattern: @example [LABEL] MNEMONIC [OPERAND] [COMMENT] @end example @noindent where @samp{OPERAND} is of the form @example [ADDRESS][,INDEX][(MOD)] @end example Items between square brackets are optional, and @table @code @item LABEL Is an alphanumeric identifier (a @dfn{symbol}) which gets the current value of the location counter, and can be used in subsequent expressions. @item MNEMONIC Is a literal denoting the operation code of the instruction (e.g. @code{LDA}, @code{STA}; see @pxref{MIX instruction set}) or an assembly pseudoinstruction (e.g. @code{ORG}, @code{EQU}). @item ADDRESS Expression evaluating to the address subfield of the instruction. @item INDEX Expression evaluating to the index subfield of the instruction. It defaults to 0 (i.e., no use of indexing) and can only be used when @code{ADDRESS} is present. @item MOD Expression evaluating to the mod subfield of the instruction. Its default value, when omitted, depends on @code{OPCODE}. @item COMMENT Any number of spaces after the operand mark the beggining 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 @samp{OPERAND} field). @end table Note that spaces are @emph{not} allowed between the @code{ADDRESS}, @code{INDEX} and @code{MOD} fields if they are present. White space is used to separate the label, operation code and operand parts of the instruction@footnote{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 @sc{mdk}, @code{mixasm}, does not impose such restriction.}. We have already listed the mnemonics associated will each MIX instructions; sample MIXAL instructions representing MIX instructions are: @example HERE LDA 2000 HERE represents the current location counter LDX HERE,2(1:3) this is a comment JMP 1234 @end example @node MIXAL directives, Expressions, Basic structure, MIXAL @comment node-name, next, previous, up @subsection MIXAL directives MIXAL instructions can be either one of the MIX machine instructions (@pxref{MIX instruction set}) or one of the following assembly pseudoinstructions: @ftable @code @item ORIG Sets the value of the memory address to which following instructions will be allocated after compilation. @item EQU Used to define a symbol's value, e.g. @w{@code{SYM EQU 2*200/3}}. @item CON The value of the given expression is copied directly into the current memory address. @item ALF Takes as operand five characters, constituting the five bytes of a word which is copied directly into the current memory address. @item END Marks the end of the program. Its operand gives the start address for program execution. @end ftable The operand of @code{ORIG}, @code{EQU}, @code{CON} and @code{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, @pxref{Expressions}) or a w-expression (@pxref{W-expressions}). All MIXAL programs must contain an @code{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 @code{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 @example ORIG 2000 set the initial compilation adress NOP this instruction will be loaded at adress 2000 HLT and this one at address 2001 END 2000 end of program; execution will start at address 2000 this line is not parsed by the assembler @end example @noindent The assembler will generate two binary instructions (@code{NOP} (@w{+ 00 00 00 00 00}) and @code{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 @code{HLT} instruction, which will mark the end of program execution (but not of program compilation). The @code{EQU} directive allows the definition of symbolic names for specific values. For instance, we could rewrite the above program as follows: @example START EQU 2000 ORIG START NOP HLT END START @end example @noindent which would give rise to the same compiled code. Symbolic constants (or symbols, for short) can also be implicitly defined placing them in the @code{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 @example ORIG 2000 START NOP HLT END START @end example The @code{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 @example ORIG 1150 CON -1823473 @end example @noindent it will assign to the memory cell number 1150 the contents @w{- 00 06 61 11 49} (which corresponds to the decimal value -1823473). Finally, the @code{ALF} directive let's you specify the memory contents as a set of five (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: @example OUT MSG MSG is not yet defined here (future reference) MSG ALF "THIS " MSG gets defined here ALF "IS A " ALF "MESSA" ALF "GE. " @end example @noindent The above snippet also shows the use of a @dfn{future reference}, that is, the usage of a symbol (@code{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 (@pxref{Expressions}). @cindex comments Any line starting with an asterisk is treated as a comment and ignored by the assembler. @example * This is a comment: this line is ignored. * This line is an error: * must be in column 1. @end example As noted in the previous section, comments can also be located after the @code{MNEMONIC} field of an instruction, separated from it by white space, as in @example LABEL LDA 100 This is also a comment @end example @node Expressions, W-expressions, MIXAL directives, MIXAL @comment node-name, next, previous, up @subsection Expressions @cindex operator @cindex binary operator @cindex unary operator The @code{ADDRESS}, @code{INDEX} and @code{MOD} fields of a MIXAL instruction can be expressions, formed by numbers, identifiers and binary operators (@code{+ - * / // :}). @code{+} and @code{-} can also be used as unary operators. Order of evaluation 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, @example 4+2** @end example @noindent evaluates to 4 plus two times the current memory location. White space is not allowed within expressions. The special binary operator @code{:} has the same meaning as in fspecs, i.e., @example A:B = 8*A + B @end example @noindent while @code{A//B} stands for the quotient of the ten-byte number @w{@code{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 @code{B}. Sample expressions are: @example 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 00) @end example @noindent 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 stand-alone (or modified by an unary operator) in the @code{ADDRESS} part of a MIXAL instruction, e.g. @example * OK: stand alone future reference STA -S1(1:5) * ERROR: future reference in expression LDX 2-S1 S1 LD1 2000 @end example @node W-expressions, Local symbols, Expressions, MIXAL @comment node-name, next, previous, up @subsection W-expressions @cindex w-expressions Besides expressions, as described above (@pxref{Expressions}), the MIXAL assembler is able to handle the so called @dfn{w-expressions} as the operands of the directives @code{ORIG}, @code{EQU}, @code{CON} and @code{END} (@pxref{MIXAL directives}). The general form of a w-expression is the following: @example WEXP = EXP[(EXP)][,WEXP] @end example @noindent where @code{EXP} stands for an expression and square brackets denote optional items. Thus, a w-expression is made by a regular expression followed by an optional expression between parenthesis, followed by any number of similar constructs separated by commas. Sample w-expressions are: @example 2000 235(3) S1+3(S2),3000 S1,S2(3:5),23 @end example W-expressions are evaluated as follows. First, all expressions are evaluated according to the rules given in the previous section. Thus, if we start with, say, @samp{S1+2(2:4)} where @samp{S1} equals 265230, we have @samp{265232(2:4)}. The expression between parenthesis must be a valid f-spec, for it specifies the bytes to be taken from the preceding word. In our example, we must take 3 bytes of the word @w{@samp{+ 00 01 00 48 16}} (which is 265232), and store them in positions 2, 3 and 4 of the result, resulting in the new word @w{@samp{+ 00 00 48 16 00}} (i.e., the decimal value 197632). When we have two expressions separated with a comma, we take, for each one, the subfield specified and compose the word to obtain the result. For instance, in the w-expression @example 1(1:2),66(4:5) @end example @noindent we first take two bytes from 1 (00 and 01) and store them as bytes 1 and 2 of the result (obtaining @w{@samp{+ 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 @w{@samp{+ 00 01 00 01 02}} (262210). The process is repeated for each new comma-separated example. For instance: @example 1(1:1),2(2:2),3(3:3),4(4:4) = 01 02 03 04 00 @end example As stated before, w-expressions can only appear as the operands of MIXAL directives taking a constant value (@code{ORIG}, @code{EQU}, @code{CON} and @code{END}). Future references are @emph{not} allowed within w-expressions (i.e., all symbols appearing in a w-expression must be defined before they are used). @node Local symbols, Literal constants, W-expressions, MIXAL @comment node-name, next, previous, up @subsection Local symbols @cindex local symbols Besides user defined symbols, MIXAL programmers can use the so called @dfn{local symbols}, which are symbols of the form @code{[1-9][HBF]}. A local symbol @code{nB} refers to the address of the last previous occurrence of @code{nH} as a label, while @code{nF} refers to the next @code{nH} occurrence. Unlike user defined symbols, @code{nH} can appear multiple times in the @code{LABEL} part of different MIXAL instructions. The following code shows an instance of local symbols' usage: @example * 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 @end example Note that a @code{B} local symbol never refers to a definition in its own line, that is, in the following program: @example ORIG 1999 ST NOP 3H EQU 69 3H ENTA 3B local symbol 3B refers to 3H in previous line HLT END ST @end example @noindent the contents of @samp{rA} is set to 69 and @emph{not} to 2001. An specially tricky case occurs when using local symbols in conjunction with @code{ORIG} pseudoinstructions. To wit@footnote{The author wants to thank Philip E. King for pointing these two special cases of local symbol usage to him.}, @example 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 @end example @node Literal constants, , Local symbols, MIXAL @comment node-name, next, previous, up @subsection Literal constants @cindex literal constants MIXAL allows the introduction of @dfn{literal constants}, which are automatically stored in memory addresses after the end of the program by the assembler. Literal constants are denoted as @code{=wexp=}, where @code{exp} is an w-expression (@pxref{W-expressions}). For instance, the code @example L EQU 10 LDA =20-L= @end example causes the assembler to add after the program's end an instruction with contents 10, and to assemble the above code as the instruction @w{@code{ LDA a}}, where @code{a} stands for the address in which the value 10 is stored. In other words, the compiled code is equivalent to the following: @example L EQU 10 LDA a @dots{} a CON 20-L END start @end example @node Getting started, mixvm, MIX and MIXAL tutorial, Top @comment node-name, next, previous, up @chapter Getting started In this chapter, you will find a sample code-compile-run-debug session using the @sc{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 @ref{MIX and MIXAL tutorial}. @menu * Writing a source file:: A sample MIXAL source file. * Compiling:: Using @code{mixasm} to compile source files into binary format. * Running the program:: Running and debugging your program. @end menu @node Writing a source file, Compiling, Getting started, Getting started @comment node-name, next, previous, up @section Writing a source file @cindex MIXAL @cindex source file MIXAL programs can be written as ASCII files with your editor of choice. Here you have the mandatory @emph{hello world} as written in the MIXAL assembly language: @example * (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) 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) @end example @noindent MIXAL source files should have the extension @file{.mixal} when used with the @sc{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 Knuth's definition of MIXAL each field must start at a fixed pre-defined column number, the @sc{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: @itemize @minus @item an optional label, which either refers to the current memory address (as @code{START} and @code{MSG} in lines 7 and 9) or a defined symbol (@code{TERM}) (if present, the label must always start at the first column in its line, for the first whitespace in the line maks the beginning of the second field), @item an operation mnemonic, which can represent either a MIX instruction (@code{OUT} and @code{HLT} in lines 6 and 7 above), or an assembly pseudoinstruction. @item an optional operand for the (pseudo)instruction, and @item an optional free text comment. @end itemize @noindent Lines 9-12 of the @file{hello.mixal} file above also show the second (and last) difference between Knuth's MIXAL definition and ours: the operand of the @code{ALF} pseudoinstruction (a word of five characters) must be quoted with using ""@footnote{In Knuth's definition, the operand always starts at a fixed column number, and the use of quotation is therefore unnecessary. As @code{mixasm} releases this requirement, marking the beginning and end of the @code{ALF} operand disambiguates the parser's recognition of this operand when it includes blanks}. The workings of this sample program should be straightforward if you are familiar with MIXAL. See TAOCP vol. 1 for a thorought definition or @ref{MIX and MIXAL tutorial}, for a quick tutorial. @node Compiling, Running the program, Writing a source file, Getting started @comment node-name, next, previous, up @section Compiling @cindex compiling @cindex binary programs @cindex virtual machine @cindex assembler @cindex @code{mixasm} A simulator of the MIX computer, called @code{mixvm} (MIX virtual machine) is included in the @sc{mdk} tools. It is able to run binary files containing MIX instructions written in their binary representation. You can translate MIXAL source files into this binary form using @code{mixasm}, the MIXAL assembler. So, in order to compile the @file{hello.mixal} file, you can type the following command at your shell prompt: @example mixasm -g hello @key{RET} @end example If the source file contains no errors, this will produce a binary file called @file{hello.mix} which can be loaded and run by the MIX virtual machine. The @code{-g} flag tells the assembler to include debug information in the executable file (for a complete description of all the compilation options, see @ref{mixasm}.) Now, your are ready to run your first MIX program, as described in the following section. @node Running the program, , Compiling, Getting started @comment node-name, next, previous, up @section Running the program @cindex @code{mixvm} @cindex non-interactive mode @cindex interactive mode MIX is a mythical computer, so it is no use ordering it from your favorite hardware provider. @sc{mdk} provides a software simulator of the computer, though. It is called @code{mixvm}, which stands for @dfn{MIX virtual machine}. Using it, you can run your MIXAL programs, after compiling them with @code{mixasm} into binary @file{.mix} files. @code{mixvm} can be used either in @dfn{interactive} or @dfn{non-interactive} mode. In the second case, @code{mixvm} will load your program into memory, execute it (producing any output due to MIXAL @code{OUT} instructions present in the program), and exit when it encounters a @code{HLT} instruction. In interactive mode, you will enter a shell prompt which allows you issuing commands to the running virtual machine. This commands will permit you loading, running and debugging programs, as well as inspecting the MIX computer state (register contents, memory cells contents and so on). @menu * Non-interactive mode:: Running your programs non-interactively. * Interactive mode:: Running programs interactively. * Debugging:: Commands for debugging your programs. @end menu @node Non-interactive mode, Interactive mode, Running the program, Running the program @comment node-name, next, previous, up @subsection Non-interactive mode @cindex non-interactive mode To make @code{mixvm} work in non-interactive mode, use the @code{-r} flag. Thus, to run our @file{hello.mix} program, simply type @example mixvm -r hello @key{RET} @end example @noindent at your command prompt, and you will get the following output: @example MIXAL HELLO WORLD ** Execution time: 11 @end example @noindent Since our hello world program uses MIX's device number 19 as its output device (@pxref{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.), @code{mixvm} would have created a file named after the device used (e.g. @file{disk4.dev}) and written its output there. Note also that the virtual machine reports the execution time of the program, according to the (virtual) time spent in each of the binary instructions (@pxref{Execution times}). Sometimes, you will prefer to store the results of your program in MIX registers rather than writing them to a device. In such cases, @code{mixvm}'s @code{-d} flag is your friend: it makes @code{mixvm} to dump the contents of its registers and flags after executing the loaded program. For instance, typing the following command at your shell's prompt @example mixvm -d -r hello @end example @noindent you will obtain the following output: @example MIXAL HELLO WORLD ** Execution time: 11 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 @end example @noindent 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. Enter interactive mode. @node Interactive mode, Debugging, Non-interactive mode, Running the program @comment node-name, next, previous, up @subsection Interactive mode @cindex interactive mode To enter the MIX virtual machine interactive mode, simply type @example mixvm @key{RET} @end example @noindent at your shell command prompt. This command enters the @code{mixvm} command shell. You will be presented the following command prompt: @example MIX > @end example @noindent The virtual machine is initialised and ready to accept your commands. The @code{mixvm} command shell uses GNU's readline, so that you have at your disposal command completion (using @key{TAB}) 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 @ref{Command Line Editing,,,Readline}.) Usually, the first thing you will want to do is loading a compiled MIX program into memory. This is acomplished by the @code{load} command, which takes as an argument the name of the @file{.mix} file to be loaded. Thus, typing @example MIX > load hello @key{RET} Program loaded. Start address: 3000 MIX > @end example @noindent will load @file{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 @code{pc}: @example MIX > pc Current address: 3000 MIX > @end example After loading it, you are ready to run the program, using, as you surely have guessed, the @code{run} command: @example MIX > run Running ... MIXAL HELLO WORLD ... done Elapsed time: 11 /Total program time: 11 (Total uptime: 11) MIX > @end example @noindent 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). After running the program, the program counter will point to the address after the one containing the @code{HLT} instruction. In our case, asking the value of the program counter after executing the program will give us @example MIX > pc Current address: 3002 MIX > @end example @noindent You can check the contents of a memory cell giving its address as an argument of the command @code{pmem}, like this @example MIX > pmem 3001 3001: + 00 00 00 02 05 (0000000133) MIX > @end example @noindent and convince yourself that address 3001 contains the binary representation of the instruction @code{HLT}. An address range of the form FROM-TO can also be used as the argument of @code{pmem}: @example 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 > @end example @noindent 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 @example MIX > preg A rA: + 00 00 00 00 00 (0000000000) MIX > @end example @noindent Use the comand @code{help} to obtain a list of all available commands, and @code{help COMMAND} for help on a specific command, e.g. @example MIX > help run run Run loaded or given MIX code file. Usage: run [FILENAME] MIX > @end example @noindent For a complete list of commands available at the MIX propmt, @xref{mixvm}. In the following subsection, you will find a quick tour over commands useful for debugging your programs. @node Debugging, , Interactive mode, Running the program @comment node-name, next, previous, up @subsection Debugging commands The interactive mode of @code{mixvm} lets you step by step execution of programs as well as breakpoint setting. Use @code{next} to step through the program, running its instructions one by one. To run our two-instruction @file{hello.mix} sample you can do the following: @example 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 > @end example @noindent (As an aside, the above sample also shows how the virtual machine handles cummulative time statistics and automatic program restart). You can set a breakpoint at a given address using the command @code{sbpa} (set breakpoint at address). When a breakpoint is set, @code{run} will stop before executing the instruction at the given address. Typing @code{run} again will resume program execution. Coming back to our hello world example, we would have: @example 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 > @end example @noindent Note that, since we compiled @file{hello.mixal} with debug info enabled (the @code{-g} flag of @code{mixasm}), 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 @code{sbp LINE_NO}, e.g. @example MIX > sbp 4 Breakpoint set at line 7 MIX > @end example @noindent @code{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 @code{cbpa ADDRESS} and @code{cbp LINE_NO}, or @code{cabp} to remove all currently set breakpoints. MIXAL lets you define symbolic constants, either using the @code{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 @code{psym} command. For our hello world sample, you will obtain the following output: @example MIX > psym START: 3000 TERM: 19 MSG: 3002 MIX > @end example Other useful commands for debugging are @code{tron} (which turns on tracing of executed intructions) and @code{weval} (which evaluates w-expressions on the fly). For a complete description of all available MIX commands, @xref{mixvm}. @node mixvm, mixasm, Getting started, Top @comment node-name, next, previous, up @chapter @code{mixvm}, the MIX computer simulator @cindex mixvm This chapter describes @code{mixvm}, the MIX computer simulator. @code{mixvm} is a command line interface programme which simulates the MIX computer (@pxref{The MIX computer}). It is able to run MIXAL programs (@pxref{MIXAL}) previously compiled with the MIX assembler (@pxref{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 @code{mixvm} usage, @xref{Running the program}. @menu * Invocation:: Options when invoking @code{mixvm}. * Commands:: Commands available in interactive mode. * Devices:: MIX block devices implementation. @end menu @node Invocation, Commands, mixvm, mixvm @comment node-name, next, previous, up @section Invoking @code{mixvm} @code{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): @example mixvm [-vhurd] [--version] [--help] [--usage] [--run] [--dump] [FILE[.mix]] @end example @noindent The meaning of these options is as follows: @defopt -v @defoptx --version Prints version and copyleft information and exits. @end defopt @defopt -h @defoptx --help @defoptx -u @defoptx --usage Prints a summary of available options and exits. @end defopt @defopt -r @defoptx --run Loads the specified @var{FILE} and executes it. After the program execution, @code{mixvm} exits. @var{FILE} must be the name of a binary @file{.mix} program compiled with @code{mixasm}. If your program does not produce any output, use the @code{-d} flag (see below) to peek at the virtual machine's state after execution. @end defopt @defopt -d @defoptx --dump This option must be used in conjuction with @code{-r}, and tells @code{mixvm} to print the value of the virtual machine's registers, comparison flag and overflow toggle after executing the program named @var{FILE}. See @xref{Non-interactive mode}, for sample usage. @end defopt When run without the @code{-r} flag, @code{mixvm} enters its interactive mode, showing you a prompt like this one: @example MIX > @end example @noindent and waiting for your commands (@pxref{Commands}). If the optional @var{FILE} argument is given, the file @file{FILE.mix} will be loaded into the virtual machine memory before entering the interactive mode. @node Commands, Devices, Invocation, mixvm @comment node-name, next, previous, up @section Interactive commands You can enter the interactive mode of the MIX virtual machine by simply invoking @code{mixvm} without arguments. You will then presented a shell prompt @example MIX > @end example @noindent 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 @code{bash} shell). As a beginner, your best friend will be the @code{help} command, which shows you a summary of all available MIX commands and their usage; its syntax is as follows: @deffn {@code{mixvm} command} help [command] @deffnx {@code{mixvm} command} ? [command] Prints a short description of the given @var{command} and its usage. If @var{command} is omitted, all available commands are described. @end deffn @menu * File commands:: Loading and executing programs. * Debug commands:: Debugging programs. * State commands:: Inspecting the virtual machine state. @end menu @node File commands, Debug commands, Commands, Commands @comment node-name, next, previous, up @subsection 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: @deffn {file command} load file[.mix] This command loads a binary file, @var{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 @code{END} pseudoinstruction. Thus, if your @file{sample.mixal} source file contains the line: @example END 3000 @end example @noindent and you compile it with @code{mixasm} to produce the binary file @file{sample.mix}, you will load it into the virtual machine as follows: @example MIX > load sample Program loaded. Start address: 3000 MIX > @end example @end deffn @deffn {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 @code{load}, will run the loaded program until either a @code{HLT} instruction or a breakpoint is found. If you provide a MIX filename as argument, the given file will be loaded (as with @code{load} @var{file}) and executed. If @code{run} is invoked again after program execution completion (i.e., after the @code{HLT} instruction has been found in a previous run), the program counter is repositioned and execution starts again from the beginning. @end deffn @deffn {file command} edit file[.mixal] The source file @var{file.mixal} is edited using the editor defined in the environment variable @var{MDK_EDITOR}. If this variable is not set, the following ones are tried out in order: @var{X_EDITOR}, @var{EDITOR} and @var{VISUAL}. @end deffn @deffn {file command} compile file[.mixal] The source file @var{file.mixal} is compiled (with debug information enabled) using @code{mixasm}. @end deffn @node Debug commands, State commands, File commands, Commands @comment node-name, next, previous, up @subsection Debug commands Sequential execution of loaded programs can be interrupted using the following debug commands: @deffn {debug command} next [ins_number] This command causes the virtual machine to fetch and execute up to @var{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. @end deffn @deffn {debug command} sbp line_number 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 @code{ORIG} or @code{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 @file{hello.mixal} file: @example * (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) ... @end example @noindent trying to set a breakpoint at line 5, will produce the following result: @example MIX > sbp 5 Breakpoint set at line 7 MIX > @end example @noindent since line 7 is the first one compiled into a MIX instruction (at address 3000). In order to @code{sbp} to work, the source file must be compiled using the @code{-g} flags, which tells @code{mixasm} to include debug information in the binary @file{.mix} file. @end deffn @deffn {debug command} spba address Sets a breakpoint at the given memory @var{address}. The argument must be a valid MIX memory address, i.e., it must belong into the range @w{[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 @code{sbpa}. @end deffn @deffn {debug command} cbp line_no Clears a (previously set) breakpoint at the given source file line. @end deffn @deffn {debug command} cbpa address Clears a (previously set) breakpoint at the given memory address. @end deffn @deffn {debug command} cabp Clears all currently set breakpoints. @end deffn @deffn {debug command} psym [symbol_name] MIXAL programs can define symbolic constants, using either the @code{EQU} pseudoinstruction or a label at the beginning of a line. Thus, in the program fragment @example VAR EQU 2168 ORIG 4000 START LDA VAR @end example @noindent the symbol @code{VAR} stands for the value 2168, while @code{START} is assigned the value 4000. When MIXAL programs are compiled using the @code{-g} flag (which tells @code{mixasm} to include debug information in the binary @file{.mix} file), the symbol table can be consulted from the @code{mixvm} command line using @code{psym} followed by the name of the symbol whose contents you are interested in. When run without arguments, @code{psym} will print all defined symbols and their values. @end deffn The virtual machine can also show you the instructions it is executing, using the following commands: @deffn {debug command} tron @deffnx troff @code{tron} enables instruction tracing. When tracing is enabled, each time the virtual machine executes an instruction (due to your issuing a @code{run} or @code{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 disable with the @code{troff} command. A typical tracing session could be like this: @example MIX > tron Instruction tracing has been turned 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 > troff Instruction tracing has been turned OFF. MIX > @end example @noindent 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. @end deffn @code{mixvm} is also able of evaluating w-expressions (@pxref{W-expressions}) using the following command: @deffn {debug command} weval WEXP Evaluates the given w-expression, @var{WEXP}. The w-expression can contain any currently defined symbol. For instance: @example MIX > psym START + 00 00 00 46 56 (0000003000) MIX > weval START(0:1),START(3:4) + 56 00 46 56 00 (0939716096) MIX > @end example @end deffn New symbols can be defined using the @code{ssym} command: @deffn {debug command} ssym SYM WEXP Defines the symbol named @var{SYM} with the value resulting from evaluating @var{WEXP}, an w-expression. The newly defined symbol can be used in subsequent @code{weval} commands, as part of the expression to be evaluated. E.g., @example 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 > @end example @end deffn Finally, if you want to discover which is the decimal value of a MIX word expressed as five bytes plus sign, you can use @deffn {debug command} w2d WORD Computes the decimal value of the given word. @var{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 @code{weval}. For instance: @example MIX > w2d - 01 00 00 02 02 -16777346 MIX > weval -16777346 - 01 00 00 02 02 (0016777346) MIX > @end example @end deffn @node State commands, , Debug commands, Commands @comment node-name, next, previous, up @subsection State commands Inspection and modification of the virtual machine state (memory, registers, overflow toggle and comparison flag contents) is accomplished using the following commands: @deffn {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. @end deffn @deffn {state command} preg [A | X | J | I[1-6]] @deffnx {state command} pall @deffnx {state command} sreg A | X | J | I[1-6] value @code{preg} prints the contents of a given MIX register. For instance, @w{@code{preg} @var{A}} will print the contents of the A-register. When invoked without arguments, all registers shall be printed: @example 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 > @end example As you can see in the above sample, the contents is printed as the sign plus the values of the MIX bytes stored in the register and, between parenthesis, the decimal representation of its module. @code{pall} prints the contents of all registers plus the comparison flag and overflow toggle. Finally, @code{sreg} Sets the contents of the given register to @var{value}, expressed as a decimal constant. If @var{value} exceeds the maximum value storable in the given register, @math{VALUE mod MAXIMU_VALUE} is stored, e.g. @example MIX > sreg I1 1000 MIX > preg I1 rI1: + 15 40 (1000) MIX > sreg I1 1000000 MIX > preg I1 rI1: + 09 00 (0576) MIX > @end example @end deffn @deffn {state command} pflags @deffnx {state command} scmp E | G | L @deffnx {state command} sover F | T @code{pflags} prints the value of the comparison flag and overflow toggle of the virtual machine, e.g. @example MIX > pflags Overflow: F Cmp: E MIX > @end example @noindent The values of the overflow toggle are either @var{F} (false) or @var{T} (true), and, for the comparison flag, @var{E}, @var{G}, @var{L} (equal, greater, lesser). @code{scmp} and @code{sover} are setters of the comparison flag and overflow toggle values. @end deffn @deffn {state command} pmem from[-to] @deffnx {state command} smem address value @code{pmem} prints the contents of memory cells in the address range @w{[@var{FROM}-@var{TO}]}. If the upper limit @var{to} is omitted, only the contents of the memory cell with address @var{FROM} is printed, as in @example MIX > pmem 3000 3000: + 46 58 00 19 37 (0786957541) MIX > @end example The memory contents is 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. @code{smem} sets the content of the memory cell with address @var{address} to @var{value}, expressed as a decimal constant. @end deffn Finally, you can use the @code{quit} command to exit @code{mixvm}. @node Devices, , Commands, mixvm @comment node-name, next, previous, up @section MIX block devices The MIX computer comes equipped with a set of block devices for input-output operations (@pxref{Input-output operators}). @code{mixvm} implements these block devices as disk files, with the exception of block device no. 19 (typewriter terminal) which is redirected to standard output. When you request an output operation on any other (output) device, a file named according to the following table will be created in the current directory, 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). @multitable {the device name} {xx-xx} {filena[x-x].dev} {bin i/o} @item @emph{Device} @tab @emph{No.} @tab @emph{filename} @tab @emph{type} @item Tape @tab 0-7 @tab @file{tape[0-7].dev} @tab bin i/o @item Disks @tab 8-15 @tab @file{disk[0-7].dev} @tab bin i/o @item Card reader @tab 16 @tab @file{cardrd.dev} @tab char in @item Card writer @tab 17 @tab @file{cardwr.dev} @tab char out @item Line printer @tab 18 @tab @file{printer.dev} @tab char out @item Terminal @tab 19 @tab @code{stdout} @tab char out @item Paper tape @tab 20 @tab @file{paper.dev} @tab char out @end multitable @node mixasm, Copying, mixvm, Top @comment node-name, next, previous, up @chapter @code{mixasm}, the MIXAL assembler @cindex @code{mixasm} @cindex MIXAL @cindex assembler MIX programs, as executed by @code{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 (@pxref{MIXAL}) which is compiled into binary form by @code{mixasm}, the MIXAL assembler included in @sc{mdk}. In this chapter, you will find a complete description of @code{mixasm} options. @menu * Invoking @code{mixasm}:: @code{mixasm} options @end menu @node Invoking @code{mixasm}, , mixasm, mixasm @comment node-name, next, previous, up @section Invoking @code{mixasm} In its simplest form, @code{mixasm} is invoked with a single argument, which is the name of the MIXAL file to be compiled, e.g. @example mixasm hello @end example @noindent will compile either @file{hello} or @file{hello.mixal}, producing a binary file named @file{hello.mix} if no errors are found. In addition, @code{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): @example mixasm [-vhulg] [-o OUTPUT_FILE] [--version] [--help] [--usage] [--debug] [--output=OUTPUT_FILE] [--list[=LIST_FILE]] file @end example @noindent The meaning of these options is as follows: @defopt -v @defoptx --version Prints version and copyleft information and exits. @end defopt @defopt -h @defoptx --help @defoptx -u @defoptx --usage Prints a summary of available options and exits. @end defopt @defopt -g @defoptx --debug Includes debugging information in the compiled file, allowing breakpoint setting at source level and symbol table inspection under @code{mixvm}. @end defopt @defopt -o output_file @defoptx --output=output_file By default, the given source file @var{file.mixal} is compiled into @var{file.mix}. You can provide a different name for the output file using this option. @end defopt @defopt -l @defoptx --list[=list_file] This option causes @code{mixasm} to produce, in addion to the @file{.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 @file{.mls} if no argument is provided; otherwise, the listing file is named according to the argument. @end defopt @node Copying, Problems, mixasm, Top @chapter Copying @lowersections @include gpl.texi @raisesections @node Problems, Concept Index, Copying, Top @chapter Reporting Bugs @cindex bugs @cindex problems If you find a bug in @sc{mdk} (or have questions, comments or suggestions about it), please send electronic mail to @email{jaortega@@acm.org, the author}. In your report, please include the version number, which you can find by running @w{@samp{mixasm --version}}. Also include in your message the output that the program produced and the output you expected. @node Concept Index, , Problems, Top @unnumbered Concept Index @cindex tail recursion @printindex cp @c @node MIXAL instructions, , Concept Index, Top @comment node-name, next, previous, up @c @unnumbered MIXAL instructions @c @printindex fn @shortcontents @contents @bye