Which RCX extractor rules to use?

[vijayank88]

In sky130A PDK selection RCX extraction rules follows caliber

set ::env(RCX_RULES) {/OpenLane/pdks/sky130A/libs.tech/openlane/rules.openrcx.sky130A.nom.calibre}
set ::env(RCX_RULES_MAX) {/OpenLane/pdks/sky130A/libs.tech/openlane/rules.openrcx.sky130A.max.calibre}
set ::env(RCX_RULES_MIN) {/OpenLane/pdks/sky130A/libs.tech/openlane/rules.openrcx.sky130A.min.calibre}

In sky130B PDK selection RCX extraction rules follows spef_extractor

set ::env(RCX_RULES) {/OpenLane/pdks/sky130B/libs.tech/openlane/rules.openrcx.sky130B.nom.spef_extractor}
set ::env(RCX_RULES_MAX) {/OpenLane/pdks/sky130B/libs.tech/openlane/rules.openrcx.sky130B.max.spef_extractor}
set ::env(RCX_RULES_MIN) {/OpenLane/pdks/sky130B/libs.tech/openlane/rules.openrcx.sky130B.min.spef_extractor}

How this RCX_RULES selected for sky130A and sky130B PDK? (Configuration which control the selection)

Some of MPW designs which passed signoff time previously, after introduction of this RCX_RULES failed to meet signoff timing with sky130A.
After debugging its found that change in RCX_RULES for sky130A & sky130B.
So please confirm which RCX_RULES to use for signoff timing check.

cc/ @RTimothyEdwards @donn

[donn]

@vijayank88 We picked the one that is most accurate for each variant of sky130. For sky130A, we've been able to source a calibration made with Calibre, which we believe to be the most accurate one available. For sky130B, we have no such calibration, so we fall back on the one done with spef_extractor.

If a design fails timing with the new calibration, it has to be updated. Reverting to the old parasitics is not acceptable.

[maliberty]

What is needed to get a similar calibration for B?

[donn]

That is a very good question. @RTimothyEdwards?

[tspyrou]

@vijayank88 how different are the numbers between the two?