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  3. Issue with Saved Nodes Being Filtered During Spectre PS...

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Issue with Saved Nodes Being Filtered During Spectre PSS

Alireza Razzaghi
Alireza Razzaghi 3 hours ago

Hi Andrew,
I’m currently using the “selected” option under Save Options → Select signals to output (save) in Spectre. I also include a text file under Simulation Files → Definition Files containing several save statements such as:
save X1.* depth=2
save X1.X2.* depth=3
save X1.X2.X3.* depth=4

In this setup, X1 contains a block with LVS-resistor parasitics, which breaks connectivity along the paths where I want to extract and save parasitic nodes. This combined approach had been working well until recently, when I noticed that in pss and transient analyses Spectre began filtering out some nodes that should have been saved.
To diagnose this, I added the following under Options → Analog → Miscellaneous → Additional arguments:
dump_wildcard_info=yes

This generated the input.wildcard.out file. After examining it, I observed that, for example, Spectre reported:
save X1.* nodes: 35

but only 12 nodes were actually listed under that wildcard. Searching the simulator log revealed this warning:
WARNING (SPECTRE-8544): Ignoring internal parasitic RC nodes `CLK' in save statement because
parasitic optimization will filter out the parasitic nodes by default. Set savefilter=none
if the nodes are not to be ignored.

As suggested, I added:
savefilter=none

also under Additional arguments, and this fixed the issue for a short transient analysis. With this change I was able to see all 35 nodes in both input.wildcard.out and the Results Browser.
However, when I ran a PSS analysis, although input.wildcard.out still listed all 35 nodes, the Results Browser again displayed only a subset of them. It appears that Spectre is dropping some nodes during PSS, but I am not sure why.
Would you please share any insight into how I can ensure that Spectre retains all nodes without applying additional filtering, especially for PSS?
Best regards,
Alireza

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