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Section 24
Program Trace Routine
The Program Trace Routine (SNOOPY) is a routine that traces through programs. It is
used with assembly language programs. In batch mode, SNOOPY provides information
about every instruction executed and the effect it had. In demand mode, SNOOPY is a
powerful diagnostic routine that gives the caller control over the trace operation. The
following paragraphs describe how to use SNOOPY in batch mode. Large printouts may
be produced.
A program that is being traced functions the same as a program that is not being traced
except that:
• Execution time is slower. This can affect I/O timing, which might be relevant to the
program being diagnosed.
• Contingencies that would normally error terminate the activity being traced
terminate EXIT$.
The following restrictions apply to SNOOPY:
• SNOOPY must be part of the program's main segment (see the Collector
Programming Reference Manual).
• Tracing terminates if the main segment is reloaded.
• Only one activity may be traced at a time unless the caller uses duplicate copies of
SNOOPY.
• The program cannot be traced if it is running in real-time mode.
• No activity contingency routine may exist for the activity being traced.
• The only I/O Executive requests permitted are IO$ and IOW$.
• Byte instructions and J-register (character addressing) mode for the 1100/60,
1100/70, and 1100/80 are not traced. The EIS instructions for the 1100/60 and
1100/70 are not simulated.
• The major register set must be available.
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