User guide

4-4
Simulating Your Design
Save and Restart
VCS provides a save and restart feature that allows checkpoints of
the simulation to be saved at arbitrary times. The resulting checkpoint
files can be executed at a later time, causing simulation to resume at
the point immediately following the save.
Benefits of save and restart include:
• Regular checkpoints for interactively debugging problems found
during long batch runs
• Use of plusargs to start action such as $dumpvars on restart
• Execution of common simulation system tasks such as $reset
just once in a regression
Restrictions of save and restart include:
• Requires extra Verilog code to manage the save and restart
• Must duplicate start-up code if handling plusargs on restart
• File I/O suspend and resume in PLI applications must be given
special consideration
Save and Restart Example
Example 4-1 illustrates the basic functionality of save and restart.
The $save call does not execute a save immediately, but schedules
the checkpoint save at the end of the current simulation time just
before events scheduled with #0 are processed. Therefore, events
delayed with #0 are the first to be processed upon restart.