update sky130hd layers' resistance and lower gcd core utilization

[AcKoucher]

Correlation Data

Mode: segment
Designs (7): aes, chameleon, gcd, ibex, jpeg, microwatt, riscv32i.
OR Version: bfd6383488 (nightly 7017)
Units: R [kΩ/μm], C [pF/μm]

The resistance values that we were using weren't actually precise. Probably something off with the net-based regression script. The resistance fits obtained with the new segment-based regression have perfect (1.00) R².

I cleaned up the setRC.tcl script so that the data w.r.t. the correlation is tracked here rather than having comments in the file.

Observations:

• There was no regression data for the l1 layer as sky130hd designs don't route on it. The old RC values were kept.
• On the gcd design, the higher R values caused repair_timing to make more insertions which led to a DPL failure during incremental GRT. The solution was to decrease the core utilization a little bit.

Updated Rules

designs/sky130hd/chameleon/rules-base.json updates:

Metric	Old	New	Type
cts__timing__setup__ws	-0.962	-1.33	Failing
cts__timing__setup__tns	-6.72	-12.3	Failing
globalroute__antenna_diodes_count	200	249	Failing
globalroute__timing__setup__ws	-0.943	-1.26	Failing
globalroute__timing__setup__tns	-5.7	-11.4	Failing
finish__timing__setup__ws	-0.881	-1.14	Failing
finish__timing__setup__tns	-6.91	-8.2	Failing

designs/sky130hd/gcd/rules-base.json updates:

Metric	Old	New	Type
cts__timing__setup__tns	-68.8	-70.3	Failing

designs/sky130hd/jpeg/rules-base.json updates:

Metric	Old	New	Type
cts__timing__setup__tns	-59.8	-73.8	Failing
globalroute__timing__setup__tns	-113.0	-131.0	Failing
finish__timing__setup__tns	-42.2	-55.1	Failing

[WARNING] Multiple clocks not supported. Will use first clock: ext_clk: 15.0000.
designs/sky130hd/microwatt/rules-base.json updates:

Metric	Old	New	Type
cts__timing__setup__tns	-345.0	-356.0	Failing
globalroute__timing__setup__tns	-306.0	-345.0	Failing
detailedroute__antenna_diodes_count	1352	1513	Failing
finish__timing__setup__tns	-305.0	-349.0	Failing

[gemini-code-assist]

Code Review

This pull request reduces the core utilization for the gcd design in sky130hd from 40 to 38 and updates the layer resistance values for layers met1 through met5 in setRC.tcl. Feedback suggests retaining the comments in setRC.tcl that document the RC value generation method and units to ensure future maintainability and reproducibility.