User guide

6-33
VPD and EVCD File Generation
Performance Tips
The following tips explain how to manage performance of VCS and
VPD:
• Normally you should save data for all signals that you may require
for analysis. The time range should be such that it very likely
contains the origin of the problem.
• Generally, the bigger you make the RAM buffer size (via the
+vpdbufsize option), the faster the simulation completes its run.
The effects are so dependent on circuit and activity that
rules-of-thumb do not apply. Synopsys suggests doubling the
RAM size for the same simulation on your own design while
measuring VCS performance to get a figure for an appropriate
setting. When making this measurement, compare sizeable
simulation runs to overcome the effects of compile time. Naturally,
the above requires that you have physical memory to
accommodate the simulation. Swapping significantly reduces
performance.
Making the buffer size too large can cause excessive swapping,
which can dramatically slow the simulation.
• Saving line-execution data enables more efficient debug of
behavioral code. Access to such data allows breakpointing on
particular activities in the code and stepping through the exact
execution of the source. Correctly used, the cost of reporting on
line execution data (slower simulation) more than pays for itself
by enabling much faster location of the code deficiencies.