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8.2.3 Additional VM functions

When writing non-trivial Scheme extensions using the MIX/Scheme library, you will probably need to evaluate the contents of the virtual machine components (registers, memory cells and so on). For instance, you may need to store the contents of the A register in a variable. The Scheme functions described so far are of no help: you can print the contents of A using (mix-preg 'A), but you cannot define a variable containing the contents of A. To address this kind of problems, the MIX/Scheme library provides the following additional functions:

— Function: mixvm-status
— Function: mix-vm-status

Return the current status of the virtual machine, as a number (mixvm-status) or as a symbol (mix-vm-status). Posible return values are:

(mixvm-status) (mix-vm-status)
0 MIX_ERROR Loading or execution error
1 MIX_BREAK Breakpoint encountered
2 MIX_COND_BREAK Conditional breakpoint
3 MIX_HALTED Execution terminated
4 MIX_RUNNING Execution stopped after next
5 MIX_LOADED Program successfully loaded
6 MIX_EMPTY No program loaded

— Function: mix-vm-error?
— Function: mix-vm-break?
— Function: mix-vm-cond-break?
— Function: mix-vm-halted?
— Function: mix-vm-running?
— Function: mix-vm-loaded?
— Function: mix-vm-empty?

Predicates asking whether the current virtual machine status is MIX_ERROR, MIX_BREAK, etc.

— Function: mix-reg register
— Function: mix-set-reg! register value

mix-reg evaluates to a number which is the contents of the specified register. mix-set-reg sets the contents of the given register to value. The register can be specified either as a string ("A", "X", etc.) or as a symbol ('A, 'X, etc.). For instance,

          guile> (mix-reg 'A)
          2341
          guile> (mix-set-reg! "A" 2000)
          ok
          guile> (define reg-a (mix-reg 'A))
          guile> (display reg-a)
          2000
          guile>
— Function: mix-cell cell_no
— Function: mix-set-cell! cell_no value

Evaluate and set the contents of the memory cell number cell_no. Both cell_no and value are Scheme numbers.

— Function: mix-loc

Evaluates to the value of the location counter (i.e., the address of the next instruction to be executed).

— Function: mix-over
— Function: mix-set-over! #t|#f

mix-over evaluates to #t if the overflow toggle is set, and to #f otherwise. The value of the overflow toggle can be modified using mix-set-over!.

— Function: mix-cmp
— Function: mix-set-cmp! 'L|'E|'G

Evaluate and set the comparison flag. Possible values are the scheme symbols L (lesser), E (equal) and G (greater).

— Function: mix-up-time

Evaluates to the current virtual machine uptime.

— Function: mix-lap-time

Evaluates to the current virtual machine lapsed time, i.e., the time elapsed since the last run or next command.

— Function: mix-prog-time

Evaluates to the total time spent executing the currently loaded program.

— Function: mix-prog-name

Evaluates to a string containing the basename (without any leading path) of the currently loaded MIX program.

— Function: mix-prog-path

Evaluates to a string containing the full path to the currently loaded MIX program.

— Function: mix-src-path

Evaluates to a string containing the full path to the source file of the currently loaded MIX program.

— Function: mix-src-line [lineno]
— Function: mix-src-line-no

mix-src-line-no evaluates to the current source file number during the execution of a program. mix-src-line evaluates to a string containing the source file line number lineno; when invoked without argument, it evaluates to (mix-src-line (mix-src-line-no)).

— Function: mix-ddir

Evaluates to a string containing the full path of the current device directory.