mdk_mixvm.texi

汇编语言编程源代码

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 > 
@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. The
tracing behaviour is stored as a configuration parameter in @file{~/.mdk}.
@end deffn

@deffn {debug command} pline [LINE_NUMBER]
Prints the requested source line (or the current one if
@var{line_number} is omitted:

@example
MIX > load ../samples/hello
Program loaded. Start address: 3000
MIX > pline
Line 5: START       OUT   MSG(TERM)
MIX > pline 6
Line 6:             HLT   
MIX >
@end example
@end deffn

@deffn {debug command} pbt [INS_NUMBER]
This command prints a backtrace of executed instructions. Its optional
argument @var{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 (@file{bt.mixal}):

@example
    ORIG 0
BEG JMP *+1
    JMP *+1
FOO JMP BAR
BAR HLT
    END BEG
@end example

@noindent
you could get the following traces:

@example
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 >
@end example

Note that the executed instruction trace gives you the label of the
executed line or, if it has no label, its address.
@end deffn

As you have probably observed, @code{mixvm} prints timing statistics
when running programs. This behaviour can be controlled using the
@code{stime} command (@pxref{Configuration commands}).

@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, Configuration commands, Debug commands, Commands
@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} pstat
This commands prints the current virtual machine state, which can be one
of the following:
@itemize @minus
@item
No program loaded
@item
Program successfully loaded
@item
Execution stopped (@code{next} executed)
@item
Execution stopped: breakpoint encountered
@item
Execution stopped: conditional breakpoint encountered
@item
Program successfully terminated
@end itemize
@end deffn

@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} sreg A | X | J | I[1-6] value
@deffnx {state command} preg [A | X | J | I[1-6]]
@deffnx {state command} pall
@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, @code{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

@node Configuration commands, Scheme commands, State commands, Commands
@subsection Configuration commands

This section describes commands that allow you to configure the virtual
machine behaviour. This configuration is stored in the @sc{mdk}
directory @file{~/.mdk}.

As you can see in their description, some commands print, as a side
effect, informational messages to the standard output (e.g. @code{load}
prints a message telling you the loaded program's start address): these
messages can be enabled/disabled using @code{slog}:

@deffn {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 @code{p} (@code{preg}, @code{pmem} and the like).
@end deffn

@deffn {config command} stime  on|off
@deffnx {config command} ptime  
The @code{stime} command (un)sets the printing of timing statistics, and
@code{ptime} prints their current value:

@example
MIX > ptime
Elapsed time: 10 /Total program time: 11 (Total uptime: 11)
MIX >
@end example
@end deffn

@deffn {config command} sedit TEMPLATE
@deffnx {config command} pedit
@code{sedit} sets the command to be used to edit MIXAL source files with
the @code{edit} command. @var{TEMPLATE} must contain the control
characters @code{%s} to mark the place where the source's file name will
be inserted. For instance, if you type

@example
MIX > sedit emacsclient %s
MIX >
@end example

issuing the @code{mixvm} command @w{@code{edit foo.mixal}} will invoke
the operating system command @w{@code{emacsclient foo.mixal}}.

@code{pedit} prints the current value of the edit command template.

@end deffn

@deffn {config command} sasm TEMPLATE
@deffnx {config command} pasm
@code{sasm} sets the command to be used to compile MIXAL source files with
the @code{compile} command. @var{template} must contain the control
characters @code{%s} to mark the place where the source's file name will
be inserted. For instance, if you type

@example
MIX > sasm mixasm -g -l %s
MIX >
@end example

issuing the @code{mixvm} command @w{@code{compile foo.mixal}} will invoke
the operating system command @w{@code{mixasm -g -l foo.mixal}}.

@code{pasm} prints the current value of the compile command template.

@end deffn

@deffn {config command} sddir DIRNAME
@deffnx {config command} pddir
MIX devices (@pxref{Devices}) are implemented as regular files stored,
by default, inside @file{~/.mdk}. The @code{sddir} command lets you
specify an alternative location for storing these device files, while
@code{pddir} prints the current device directory.
@end deffn

Finally, you can change the default command prompt, @samp{MIX > },
using the @code{prompt} command:

@deffn {config command} prompt PROMPT
Changes the command prompt to @var{prompt}. If you want to include
white space(s) at the end of the new prompt, bracket @var{prompt} using
double quotes (e.g., @code{prompt ">> "}).
@end deffn

@node Scheme commands,  , Configuration commands, Commands
@subsection Scheme commands

If you have compiled @sc{mdk} with @code{libguile} support
(@pxref{Special configure flags}), @code{mixvm} will start and
initialise an embedded Guile Scheme interpret when it is invoked. That
means that you have at your disposal, at @code{mixvm}'s command prompt,
all the Scheme primitives described in @ref{Using mixguile} and
@ref{mixguile}, as well as any other function or hook that you have
defined in the initialisation file @file{~/.mdk/mixguile.scm}. To
evaluate a Scheme function, simply type it at the @code{mixvm} command
prompt (see @ref{Using Scheme in mixvm and gmixvm} for a
sample). Compared to the @code{mixguile} program, this has only one
limitation: the expressions used in @code{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 @code{scmf}
command:

@deffn {scheme command} scmf FILE_NAME
Loads the given Scheme file and evaluates it using the embedded Guile
interpreter. 
@end deffn


@node Devices,  , Commands, mixvm
@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, 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 @file{~/.mdk}; this location can be changed using the
@code{mixvm} command @code{devdir} (@pxref{Configuration commands}).

@multitable {the device name} { xx-xx } {filename[x-x].dev} {bin  i/o/char } 
@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