Creating a Saved State FIle during a Transient Simulation

SPectre can create a state file of a circuit periodically during a transient simulation. This file can be used to restart the simulation at some later time after the transient simulation is finished. Alternately, if the simulation terminates unexpectedly, the simulation can be restarted from the last saved state file.

Spectre used to support saving a "checkpoint" file, but I cannot find this option in version 6.1.1.436 of Spectre. However, the manual suggests that simulation recovery is far more robust when saving the state file in lieu of the checkpoint file.

When using ocean, one syntax for including a specific file to save the operating state is as follows:

TSTOP = 300e-09
sprintf( state_file "vcostate.srf")

analysis('tran ?stop TSTOP ?errpreset "conservative"  ?maxstep maxstep  ?savetime list("50e-09"
 "100e-09" "150e-09" "200e-09" "250e-09" "300e-09") ?savefile state_file)
 
This will save the circuit state at simulation times of 50 ns, 100 ns, 150 ns,...,300 ns. Following the simulation, the netlist directory will contain a distinct file for each of the time points as shown below.

Contents of netlist directory following simulation:

amap/                   netlister.log           spectre1.ocn
artSimEnvLog            paraplot-sim-out        spectre2.ocn
control                 raw/                    spectre4.ocn
ihnl/                   runSimulation*          vcostate.srf0_50.0ns
input.ahdlSimDB/        si.env                  vcostate.srf1_100.0ns
input.scllog            spectre.dc              vcostate.srf2_150.0ns
input.scs               spectre.fc              vcostate.srf3_200.0ns
map/                    spectre.ic              vcostate.srf4_250.0ns
netlist                 spectre.inp             vcostate.srf5_300.0ns
netlistFooter           spectre.sim
netlistHeader           spectre0.ocn


Two other options are to use "saveperiod" which saves the state file at a given simulation time interval and "saveclock" which saves the simulation results at the specified realtime interval. These two options, however, overwrite the previous state file. Hence, only a single state file will be contained in the simulation netlist directory. Spectre, by default, is supposed to save the state file every 30 minutes.

Using the Saved State FIle to Re-start a SImulation
----------------------------------------------------

The syntax to re-start a transient simulation from a saved state file named "input.scs.tran.srf" is as follows:

analysis('tran TSTOP  ?errpreset "conservative" ?recover "input.scs.tran.srf" )

One danger in using the recover option is that SPectre will overwrite the existing simulation data. Hence, it is best to copy the simulation results already completed (if you need them) to a new distinct directory name prior to restarting the simulation. There is a methodology to join the two simulation results that Cadence has documented.


sml 5/6/2009