Instruction step
From Wikipedia, the free encyclopedia
An instruction step is a method of executing a computer program one step at a time to determine how it is functioning. This might be to determine if the correct program flow is being followed in the program during the execution or to see if variables are set to their correct values after a single step has completed.
Contents |
[edit] Hardware instruction step
On earlier computers, a knob on the computer console may have enabled step-by-step execution mode to be selected and execution would then proceed by pressing a "single step" or "single cycle" button. Program status word / Memory or general purpose register read-out could then be accomplished by observing and noting the console lights.
[edit] Software instruction step
On later platforms with multiple users, this method was impractical and so single step execution had to be performed using software techniques.
In some software products which facilitate debugging of High level languages, it is possible to execute an entire HLL statement at a time. This frequently involves many machine instructions and execution pauses after the last instruction in the sequence, ready for the next 'instruction' step. This requires integration with the compilation output to determine the scope of each statement.
[edit] Examples of programs providing 'Software' instruction step
- OLIVER (CICS interactive test/debug) for IBM CICS, allowed both instruction and HLL statement stepping
- SIMON (Batch Interactive test/debug) for IBM batch programs, allowed both instruction and HLL statement stepping
- SIMMON an IBM internal test system which provided instruction stepping
