flow/designs: per-PDK WNS plots and README from rules-base.json

flow/designs/README.md

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+# ORFS designs
+
+## Findings: how accurate are early-stage WNS estimates?
+
+Reading the committed `rules-base.json` baselines, normalized by each design's clock
+period (parsed from its `.sdc`), the picture across the 67 designs / 8 PDKs that expose
+`cts` and `globalroute` slack is:
+
+- **Global route usually tightens the estimate.** For most PDKs the mean absolute error
+  drops from `cts` to `globalroute` — dramatically for `sky130hs` (10.5% → 1.9%) and
+  `gt2n` (3.3% → 0.0%), and clearly for `gf12` (2.2% → 1.1%) and `ihp-sg13g2`
+  (0.6% → 0.0%). `ihp-sg13g2` and `gf180` are already accurate at `cts`.
+
+- **`cts` is biased optimistic; `globalroute` often overshoots into pessimism.** Every
+  PDK's `cts` bias is ≥ 0 (cts reports more slack than the design finally closes with),
+  whereas `globalroute` bias flips negative for `sky130hd` (−3.5%), `sky130hs` (−1.9%),
+  `gf12` (−1.1%) and `nangate45` (−0.5%). Global route tends to *over-correct*.
+
+- **`sky130hd` is the exception where routing makes the estimate worse**, not better:
+  `globalroute` MAE (3.5%) exceeds `cts` MAE (2.9%), and it is consistently pessimistic.
+
+- **Outliers are design-specific, not PDK-wide.** `sky130hs/gcd` has `cts` +45.9%
+  (wildly optimistic, fully corrected by `globalroute`), and `asap7/swerv_wrapper` is
+  +14.9% optimistic at *both* stages — the cases most likely to mislead an early-stage
+  go/no-go decision.
+
+Practical reading: `cts` slack is a usable optimistic rank-ordering; `globalroute` is the
+first estimate within a few % of final for most PDKs, but on `sky130hd` (and for specific
+designs elsewhere) even `globalroute` can be off by 3–10% of the clock period. This is the
+design-level companion to the per-net GRT-vs-RCX divergence in
+[`flow/docs/rcx`](../docs/rcx/README.md) (PR #4302). Per-PDK design breakdowns:
+[asap7](asap7/README.md), [nangate45](nangate45/README.md), [sky130hd](sky130hd/README.md),
+[sky130hs](sky130hs/README.md), [gf12](gf12/README.md), [gf180](gf180/README.md),
+[gt2n](gt2n/README.md), [ihp-sg13g2](ihp-sg13g2/README.md).
+
+<!-- BEGIN WNS-ACCURACY (generated by flow/util/plot_wns.py) -->
+## WNS estimate accuracy across PDKs
+
+How closely the earlier-stage worst-slack estimates (`cts`, `globalroute`) match the final (`finish`) WNS, per design, normalized by that design's clock period so PDKs with different timing units are comparable. Error is `(stage − finish) / clock_period`; **positive = optimistic** (the stage reported more slack than the design actually closes with), negative = pessimistic. Clock period is parsed from each design's `.sdc`; designs whose period could not be parsed are omitted.
+
+![WNS estimate accuracy by stage, across PDKs](wns_accuracy.png)
+
+Mean absolute error (MAE) and mean signed error (bias), in % of clock period:
+
+| PDK | designs | cts MAE | cts bias | grt MAE | grt bias | worst (design) |
+| --- | ---: | ---: | ---: | ---: | ---: | --- |
+| asap7 | 16 | 2.8% | +1.5% | 2.9% | +1.1% | +14.9% (swerv_wrapper globalroute) |
+| gf12 | 9 | 2.2% | -2.2% | 1.1% | -1.1% | -14.2% (jpeg cts) |
+| gf180 | 5 | 1.0% | +1.0% | 0.4% | +0.3% | +4.3% (aes cts) |
+| gt2n | 3 | 3.3% | +3.3% | 0.0% | +0.0% | +10.0% (aes cts) |
+| ihp-sg13g2 | 7 | 0.6% | +0.6% | 0.0% | +0.0% | +4.5% (spi cts) |
+| nangate45 | 15 | 0.8% | +0.6% | 1.0% | -0.5% | -3.2% (black_parrot globalroute) |
+| sky130hd | 7 | 2.9% | +2.0% | 3.5% | -3.5% | -10.0% (gcd globalroute) |
+| sky130hs | 5 | 10.5% | +10.5% | 1.9% | -1.9% | +45.9% (gcd cts) |
+
+_Generated by `flow/util/plot_wns.py`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS-ACCURACY -->

flow/designs/asap7/README.md

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+# asap7 designs
+
+## Findings: worst negative slack (WNS) across asap7
+
+These notes read the committed `rules-base.json` baselines — the worst setup slack each
+design reaches at clock-tree synthesis (`cts`), global route (`globalroute`) and `finish`.
+The plot and table below are regenerated from that data by
+[`flow/util/plot_wns.py`](../../util/plot_wns.py); no flow run is needed, so the numbers
+are exactly what CI checks against.
+
+What stands out:
+
+- **Every asap7 design closes with negative setup slack.** All 18 baselines have
+  `finish` WNS < 0, so the committed asap7 constraints target clocks the flow does not
+  actually meet — these baselines track *how far short* each design lands, not timing
+  closure. `swerv_wrapper` (≈ −318) and `mock-alu` (≈ −300) are the extreme cases, an
+  order of magnitude worse than the cluster around −15 … −50 (`aes*`, `mock-cpu`,
+  `uart`, `jpeg`).
+
+- **Worst slack is often not stable across stages.** Some designs pin their critical
+  path early and barely move (`cva6`, `jpeg`, `mock-cpu`: `cts ≈ globalroute ≈ finish`).
+  Others move a lot: `swerv_wrapper` degrades from −80 at cts/globalroute to −318 at
+  finish, and `riscv32i`/`riscv32i-mock-sram` slip from ≈ −47 (cts) to ≈ −81 (finish) —
+  routing and final extraction make the path materially worse than CTS predicted.
+
+- **Global route is sometimes more pessimistic than finish.** For `gcd`
+  (cts −85.9 → globalroute −110 → finish −96.7) and `aes-block`
+  (cts −84 → globalroute −31 → finish −57) the worst-slack estimate swings between
+  stages rather than monotonically worsening. This is the same GRT-vs-post-route
+  estimate gap explored in [`flow/docs/rcx`](../../docs/rcx/README.md) (PR #4302), here
+  visible at the design level rather than per net.
+
+The takeaway for anyone using cts-stage slack as a proxy for the final result: for asap7
+it is a usable rank ordering but not a reliable magnitude — several designs move tens of
+units (and `swerv_wrapper` hundreds) between cts and finish.
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — asap7](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| swerv_wrapper | -80 | -80 | -318 |
+| mock-alu | -289 | -303 | -300 |
+| gcd | -85.9 | -110 | -96.7 |
+| gcd-ccs | -101 | -93.7 | -96.4 |
+| ethmac | -88.6 | -103 | -93.3 |
+| riscv32i-mock-sram | -47.5 | -52.8 | -81.3 |
+| riscv32i | -47.5 | -49.8 | -81.2 |
+| jpeg_lvt | -30 | -30 | -63.9 |
+| aes-block | -84.1 | -31.1 | -56.6 |
+| ibex | -79.4 | -74.3 | -52.5 |
+| cva6 | -50 | -50 | -50 |
+| uart | -47.6 | -58.7 | -49.1 |
+| jpeg | -34 | -34 | -34 |
+| aes_lvt | -18 | -18 | -26.1 |
+| aes | -28.9 | -28 | -24.2 |
+| aes-mbff | -20.8 | -19 | -20.8 |
+| mock-cpu | -16.6 | -16.6 | -16.6 |
+| ethmac_lvt | -19 | -29.5 | -15.2 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/gf12/README.md

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+# gf12 designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — gf12](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| bp_single | -632 | -470 | -227 |
+| bp_quad | -375 | -223 | -225 |
+| ariane | -257 | -214 | -212 |
+| coyote | -200 | -200 | -200 |
+| bp_dual | -758 | -100 | -165 |
+| ca53 | -100 | -100 | -100 |
+| swerv_wrapper | -75 | -75 | -75 |
+| ibex | -51 | -51 | -51 |
+| tinyRocket | -40 | -40 | -40 |
+| jpeg | -96 | -53.2 | -25 |
+| aes | -21 | -21 | -21 |
+| gcd | -21.5 | -26.3 | -14 |
+| ariane133 | -20.2409 | 0 | 0 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/gf180/README.md

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+# gf180 designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — gf180](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| aes-hybrid | -0.967 | -1.1 | -1.1 |
+| aes | -0.789 | -0.876 | -0.918 |
+| riscv32i | -0.586 | -0.659 | -0.63 |
+| ibex | -0.5 | -0.5 | -0.539 |
+| jpeg | -0.375 | -0.375 | -0.375 |
+| uart-blocks | -0.3 | -0.3 | -0.3 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/gf55/README.md

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+# gf55 designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — gf55](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| aes |  |  | 0 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/gt2n/README.md

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+# gt2n designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — gt2n](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| aes | -25 | -75.2 | -75.2 |
+| jpeg | -50 | -50 | -50 |
+| gcd | -25 | -25 | -25 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/ihp-sg13g2/README.md

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+# ihp-sg13g2 designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — ihp-sg13g2](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| i2c-gpio-expander | -1 | -1 | -1 |
+| ibex | -0.4 | -0.4 | -0.4 |
+| jpeg | -0.4 | -0.4 | -0.4 |
+| riscv32i | -0.3 | -0.3 | -0.3 |
+| aes | -0.225 | -0.225 | -0.225 |
+| gcd | -0.13 | -0.13 | -0.13 |
+| spi | 0 | -0.0426 | -0.045 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/nangate45/README.md

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+# nangate45 designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — nangate45](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| bp_quad | -150 | -150 | -150 |
+| black_parrot | -3.31 | -3.45 | -3.26 |
+| mempool_group | -2.31 | -2.31 | -2.31 |
+| swerv | -0.671 | -0.719 | -0.677 |
+| ariane133 | -0.579 | -0.569 | -0.595 |
+| swerv_wrapper | -0.344 | -0.357 | -0.35 |
+| dynamic_node | -0.362 | -0.38 | -0.344 |
+| ariane136 | -0.3 | -0.3 | -0.318 |
+| bp_be_top | -0.331 | -0.315 | -0.318 |
+| bp_multi_top | -0.24 | -0.24 | -0.24 |
+| jpeg | -0.147 | -0.165 | -0.164 |
+| tinyRocket | -0.14 | -0.168 | -0.154 |
+| bp_fe_top | -0.09 | -0.09 | -0.131 |
+| ibex | -0.11 | -0.127 | -0.11 |
+| aes | -0.041 | -0.0692 | -0.0667 |
+| gcd | -0.0529 | -0.0657 | -0.0559 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/sky130hd/README.md

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+# sky130hd designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — sky130hd](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| microwatt | -2.71 | -2.8 | -2.73 |
+| gcd | -1.36 | -1.58 | -1.47 |
+| riscv32i | -1.41 | -1.55 | -1.37 |
+| jpeg | -0.716 | -0.877 | -0.654 |
+| ibex | -0.505 | -0.576 | -0.5 |
+| aes | -0.18 | -0.554 | -0.425 |
+| chameleon | -0.321 | -0.356 | -0.282 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->

flow/designs/sky130hs/README.md

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+# sky130hs designs
+
+<!-- BEGIN WNS (generated by flow/util/plot_wns.py) -->
+## WNS
+
+Worst setup slack per design at three flow stages — clock-tree synthesis (`cts`), global route (`globalroute`) and `finish` — read from each design's `rules-base.json`. Negative means setup timing is not met. Values are in this PDK's native timing unit (ps for `asap7`, ns for most others), so they are comparable within this PDK but not across PDKs.
+
+The bar is the `finish` slack; the markers show the `cts` and `globalroute` slack for the same design, so stage-to-stage movement is visible.
+
+![WNS by design — sky130hs](wns.png)
+
+| design | cts | globalroute | finish |
+| --- | ---: | ---: | ---: |
+| gcd | -0.358 | -1 | -1 |
+| riscv32i | -0.303 | -0.695 | -0.571 |
+| ibex | -0.35 | -0.525 | -0.35 |
+| jpeg | -0.2 | -0.268 | -0.2 |
+| aes | -0.14 | -0.206 | -0.145 |
+
+_Generated by `flow/util/plot_wns.py` from `rules-base.json`; regenerate with `python3 flow/util/plot_wns.py`._
+<!-- END WNS -->