rsz: extract detailed routing parasitics inside estimate_parasitics code

[eder-matheus]

Part one to fix #6064.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[maliberty]

Suggested change

	[-ext_model_file]
	[-ext_model_file model_file]

[gadfort]

how does this handle corners? they have separate model files.

[eder-matheus]

In my tests, I'm using only the public PDKs available in ORFS, which use only on model file and one corner for parasitics extraction.

How are you using multiple corners in your flow? Do you loop over each corner to extract the parasitics for them?

[gadfort]

Yes, we loop over them to generate a different spef file per corner and read them in per corner to be able to get timing across corners (it's clumsy, but it's the interface we have in OpenROAD at the moment). I think corner support is needed for this to be a complete/correct solution.

[gadfort]

If rcx was augmented to allow us to set the model files per corner that would also allow us to avoid adding this argument and just ask rcx to generate the parasitics

[eder-matheus]

Maybe this option can be updated to take multiple files, and them the implementation will perform parasitics extraction for each of them. I believe sta have the support to have the parasitics stored for multiple corners, so when running repair_timing it would look at all of them.

[gadfort]

@eder-matheus it seems to me like modifying RCX to store the model files would require a much less complex argument to this command. and yes, STA fully supports corners.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[maliberty]

@gadfort do you have a snippet of code that shows how you set it up today for rcx & sta?

[gadfort]

@maliberty https://github.com/siliconcompiler/siliconcompiler/blob/adb451bc72eb0f9b8a863ddf192a164b7f0b0e25/siliconcompiler/tools/openroad/scripts/sc_export.tcl#L40-L69
First few lines handle generate unique SPEFs for each corner and then the last bit just reads them in per corner.
In most other tools, you just define a pexcorner and associate the extraction file with that and then when you call for parasitics these are used. usually write_spef is available and takes a corner input to allow you to dump any corner you want.

[gadfort]

I should note that it looks like rcx could "handle" corners if they are in the RCX file, but the current conversion flows we have don't support creating a single file with multiple corners (no clue what that would look like anyways), most PDKs separate the corners for PEX

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"

[eder-matheus]

The current implementation of RCX doesn't allow reading multiple model files at once. Since we have a big update ongoing on RCX, I think we should not implement new features in this tool until they are merged.

Regarding my implementation here, I believe we could merge what we have now but keep track of the required updates in RCX regarding multiple model files. I will add comments in my code to track what parts needs to be updated once RCX has full support for multiple model files.