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Simulators >> Circuit Simulators >> Spectre - Time consumption of the topology check
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Message started by haikom on May 30^th, 2007, 1:51pm

Title: Spectre - Time consumption of the topology check
Post by haikom on May 30^th, 2007, 1:51pm

Hi,

I'm doing SPICE-level simulation of mixed signal circuits. One simulation takes 1/2 hour. But when I have a look at the file spectre.out, the computing time is only 5 to 7 minutes. So what takes the rest of the time? Saving the data at the harddisk, IDLE states of the spectre-process, or the topology check which is done before the simulation.
I assume that the topology check takes the rest of the time. Is this correct?
If yes, can I save this information to do this process only one time?

As I know during the topology check the schematic is scanned for floting nodes and gmin or cmin are added. So maybe this process has to be done before every simulation?
I'm happy about any comment :)

Kind regards,
haikom

Title: Re: Spectre - Time consumption of the topology che
Post by Ken Kundert on May 30^th, 2007, 10:46pm

In Spectre, the topology check is very fast. In a half hour simulation it should take no more than a second or two.

-Ken

Title: Re: Spectre - Time consumption of the topology che
Post by didac on May 30^th, 2007, 11:30pm

Are you running your simulation in a shared computer?If it's linux base I think that the computing time is the real time that the process had acceded to the CPU while if there many users you will see this kind of slow-down because they also access to the CPU thus increasing your total simulation time.

Title: Re: Spectre - Time consumption of the topology che
Post by haikom on May 31^st, 2007, 4:20am

Hi,

thanks for your answers. I'm still wondering about the time consumption. Here are more details about the simulation:
Parameter topcheck = full
Total analysis time: 25min
- Simulation preprocessing 20min (all processes after "Simulating input.scs" til "Transient Analysis..." including topology check)
- Transient analysis 5min (Initial condition solution 78sec, Intrinsic tran analysis 240sec)
Parameter topcheck = no
Total analysis time: 50min
- Simulation proprocessing 37min
- Transient analysis 13min

Ken, you said the topology check takes only a few seconds. But what is spectre doing 20min / 37min before the transient analysis? There are a lot of warnings like "rs has been deleted because its value was smaller then 'minr' ". Is this done during the topology check?

Kind regards,
haikom

Title: Re: Spectre - Time consumption of the topology che
Post by ywguo on Jun 3^rd, 2007, 11:22pm

Hi, Haikom,

Are you running a post-layout simulation?

Quote:

There are a lot of warnings like "rs has been deleted because its value was smaller then 'minr' ".

It looks that the netlist has many many very small resistors. I guess the netlist file size is very large because it contains all parasitics in layout. So it is very clear that the total analysis time increase to 50min when parameter topcheck=no. I guess that there are no warnings like "rs has been deleted because its value was smaller than 'minr' ".

Best regards,
Yawei

Title: Re: Spectre - Time consumption of the topology che
Post by Andrew Beckett on Jun 4^th, 2007, 12:55pm

It might be useful to give a bigger segment of the spectre.out file, including the circuit inventory, and so on. Perhaps its taking a long time to do the dc solution? It's very hard to tell from a small snapshot (I assume that was two snapshots from different simulations? It wasn't very clear).

Regards,

Andrew.