mdk_gstart.texi

汇编语言编程源代码

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

@cindex @code{preg}
@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

@cindex @code{help}
@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

@cindex @code{next}
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).

@cindex @code{sbpa}
@cindex breakpoints

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

@cindex @code{sbp}
@cindex breakpoints
@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. You can also set
conditional breakpoints, i.e., tell @code{mixvm} to interrupt program
execution whenever a register, a memory cell, the comparison flag or the
overflow toggle change using the commands @w{@code{sbp[rmco]}}
(@pxref{Debug commands}).

@cindex @code{psym}
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{strace} (which turns on
tracing of executed intructions), @code{pbt} (which prints a backtrace
of executed instructions) and @code{weval} (which evaluates
w-expressions on the fly). For a complete description of all available
MIX commands, @xref{mixvm}.

@node Using mixguile, Using Scheme in mixvm and gmixvm, Running the program, Getting started
@section Using @code{mixguile}

With @code{mixguile} you can run a MIX simulator embedded in a Guile
shell, that is, using Scheme functions and programs. As with
@code{mixvm}, @code{mixguile} can be run both in interactive and
non-interactive modes. The following subsections provide a quick tour on
using this MIX emulator.

@menu
* The mixguile shell::          Using the Scheme MIX virtual machine.
* Additional functions::        Scheme functions accessing the VM.
* Defining new functions::      Defining your own Scheme functions.
* Hook functions::              Using command and break hook functions.
* Scheme scripts::              
@end menu

@node The mixguile shell, Additional functions, Using mixguile, Using mixguile
@subsection The @code{mixguile} shell
@cindex Scheme
@cindex @code{mixguile}
@cindex REPL

If you simply type

@example
mixguile @key{RET}
@end example
@noindent
at the command prompt, you'll be presented a Guile shell prompt like
this

@example
guile>
@end example
@noindent
At this point, you have entered a Scheme read-eval-print loop (REPL)
which offers you all the Guile functionality plus a new set of built-in
procedures to execute and debug MIX programs. Each of the @code{mixvm}
commands described in the previous sections (and in @pxref{mixvm}) have
a Scheme function counterpart named after it by prepending the prefix
@code{mix-} to its name. Thus, to load our hello world program, you can
simply enter

@example
guile> (mix-load "hello")
Program loaded. Start address: 3000
guile> 
@end example
@noindent
and run it using @code{mix-run}:

@example
guile> (mix-run)
Running ...
MIXAL HELLO WORLD                                                     
... done
Elapsed time: 11 /Total program time: 11 (Total uptime: 11)
guile> 
@end example
@noindent
In the same way, you can execute it step by step using the Scheme
function @code{mix-next} or set a breakpoint:

@example
guile> (mix-sbp 4)
Breakpoint set at line 5
guile> 
@end example
@noindent
or, if you one to peek at a register contents:

@example
guile> (mix-preg 'A)
rA: + 00 00 00 00 00 (0000000000)
guile> 
@end example

You get the idea: you have at your disposal all the @code{mixvm} and
@code{gmixvm} commands by means of @code{mix-} functions. But, in case
you are wondering, this is only the beginning. You also have at your
disposal a whole Scheme interpreter, and you can, for instance, define
new functions combining the @code{mix-} and all other Scheme
primitives. In the next sections, you'll find examples of how to take
advantage of the Guile interpreter.

@node Additional functions, Defining new functions, The mixguile shell, Using mixguile
@subsection Additional MIX Scheme functions

The @code{mix-} function counterparts of the @code{mixvm} commands don't
return any value, and are evaluated only for their side-effects
(possibly including informational messages to the standard output and/or
error stream). When writting your own Scheme functions to manipulate the
MIX virtual machine within @code{mixguile} (@pxref{Defining new
functions}), you'll probably need Scheme functions returning the value
of the registers, memory cells and so on. Don't worry: @code{mixguile}
also offers you such functions. For instance, to access the (numerical)
value of a register you can use @code{mix-reg}:

@example
guile> (mix-reg 'I2)
0
guile> 
@end example
@noindent
Note that, unlike @code{(mix-preg 'I2)}, the expression @code{(mix-reg
'I2)} in the above example evaluates to a Scheme number and does not
produce any side-effect:

@example
guile> (number? (mix-reg 'I2))
#t
guile> (number? (mix-preg 'I2))
rI2: + 00 00 (0000)	
#f
guile> 
@end example

In a similar fashion, you can access the memory contents using
@code{(mix-cell)}, or the program counter using @code{(mix-loc)}:

@example
guile> (mix-cell 3000)
786957541
guile> (mix-loc)
3002
guile> 
@end example

Other functions returning the contents of the virtual machine components
are @code{mix-cmp} and @code{mix-over}, which eval to the value of the
comparison flag and the overflow toggle respectively. For a complete
list of these additional functions, @xref{mixguile}.

In the next section, we'll see a sample of using these functions to
extend @code{mixguile}'s functionality.

@node Defining new functions, Hook functions, Additional functions, Using mixguile
@subsection Defining new functions
@cindex Scheme functions

Scheme is a powerful language, and you can use it inside @code{mixguile}
to easily extend the MIX interpreter's capabilities.  For example, you
can easily define a function that loads a file, prints its name,
executes it and, finally, shows the registers contents, all in one shot:

@example
guile> (define my-load-and-run  @key{RET}
         (lambda (file)   @key{RET}
           (mix-load file)   @key{RET}
           (display "File loaded: ")   @key{RET}
           (mix-pprog)   @key{RET}
           (mix-run)   @key{RET}
           (mix-preg)))   @key{RET}
guile> 
@end example
@noindent
and use it to run your programs:

@example
guile> (my-load-and-run "hello")
Program loaded. Start address: 3000
File loaded: hello.mix
Running ...
MIXAL HELLO WORLD                                                     
... done
Elapsed time: 11 /Total program time: 11 (Total uptime: 33)
rA: + 00 00 00 00 00 (0000000000)
rX: + 00 00 00 00 00 (0000000000)
rJ: + 00 00 (0000)
rI1: + 00 00 (0000)	rI2: + 00 00 (0000)	
rI3: + 00 00 (0000)	rI4: + 00 00 (0000)	
rI5: + 00 00 (0000)	rI6: + 00 00 (0000)	
guile> 
@end example


Or, maybe, you want a function which sets a breakpoint at a specified
line number before executing it:

@example
guile> (define my-load-and-run-with-bp
         (lambda (file line)
           (mix-load file)
           (mix-sbp line)
           (mix-run)))
guile> (my-load-and-run-with-bp "samples/primes" 10)
Program loaded. Start address: 3000
Breakpoint set at line 10
Running ...
... stopped: breakpoint at line 10 (address 3001)
Elapsed time: 1 /Total program time: 1 (Total uptime: 45)
guile>
@end example

As a third example, the following function loads a program, runs it and
prints the contents of the memory between the program's start and end
addresses: