For example, assume one is in the middle of an interactive simulation. To determine how many times an address bus contained an 'X' when the address strobe went high, one can define a breakpoint and resimulate. This can be costly for a large, long simulation. A more practical alternative is to analyze simulation history. Manual analysis is a possibility.
Designers can examine waveforms or tabular output, searching for events of interest.
If the user can create an expression for the criteria of the search, then an automated analysis is possible and, perhaps, preferable. This is how the waveform display supports simulation output analysis. During both interactive and post-simulation debugging, we display recorded value changes in the waveform display. In addition to displaying value changes as waveforms, users have to be able to define arbitrary expressions defining events of interest. It should be possible to search automatically backwards or forwards through the simulation output for occurrences of these events.