fix: workaround for the sky130 poly density issue

Replace 50% of the decap_12 cells with newfill_12 cells across all Wokwi designs.

.github/workflows/gds.yaml

@@ -67,6 +67,14 @@ jobs:
           pdk_version: ${{ env.SKY130_PDK_VERSION }}
           pdk_root: ${{ env.PDK_ROOT }}
 
+      # Patch Wokwi designs to work around the poly density issue
+      - name: Patch Wokwi designs
+        working-directory: projects
+        run: |
+          for project in tt_um_wokwi_*; do
+            python ../sky130_density_fix/replace_decap.py --design $project --user-gds $project/$project.gds --replacement-gds ../sky130_density_fix/sky130_ef_sc_hd__newfill_12.gds
+          done
+
       # run OpenLane to build the GDS
       - name: Harden Chip ROM
         run: nix-shell $GITHUB_WORKSPACE/openlane2/shell.nix --run "python -m openlane tt/rom/config.json"

sky130_density_fix/README.txt

@@ -0,0 +1 @@
+sky130_ef_sc_hd__newfill_12.gds retrieved from https://github.com/RTimothyEdwards/open_pdks/blob/320597ea84b2816eb2fcc4fbe10c3874f19c92fc/sky130/custom/sky130_fd_sc_hd/gds/sky130_ef_sc_hd__newfill_12.gds

sky130_density_fix/replace_decap.py

@@ -0,0 +1,87 @@
+# SPDX-License-Identifier: Apache-2.0
+# Authors: David Lindley, Uri Shaked
+
+import argparse
+from random import random, seed
+
+import klayout.db as pya
+
+# We want reproducible results:
+seed(a=0)
+
+parser = argparse.ArgumentParser(
+    description="Replaces a given portion of a decap_12 cells with newfill_12 cells."
+)
+
+parser.add_argument("--probability", "-p", type=float, default=0.5, help="")
+
+parser.add_argument("--design-name", "-n", required=True)
+
+parser.add_argument("--from-cell-name", "-f", default="sky130_ef_sc_hd__decap_12")
+parser.add_argument("--to-cell-name", "-t", default="sky130_ef_sc_hd__newfill_12")
+
+parser.add_argument("--user-gds", "-i", required=True)
+parser.add_argument("--replacement-gds", "-r", required=True)
+
+parser.add_argument("--output-gds", "-o", required=False)
+
+
+args = parser.parse_args()
+
+probability = args.probability
+
+design_name = args.design_name
+
+from_cell_name = args.from_cell_name
+to_cell_name = args.to_cell_name
+
+user_gds = args.user_gds
+replacement_gds = args.replacement_gds
+output_gds = args.output_gds or user_gds
+
+replacement_layout = pya.Layout()
+replacement_layout.read(replacement_gds)
+
+user_layout = pya.Layout()
+user_layout.read(user_gds)
+
+top_cell = user_layout.cell(design_name)
+replacement_cell = user_layout.create_cell(to_cell_name)
+replacement_cell.copy_tree(replacement_layout.cell(to_cell_name))
+
+
+def cell_dimensions_equal(cell1, cell2):
+    return (
+        cell1.bbox().width() == cell2.bbox().width()
+        and cell1.bbox().height() == cell2.bbox().height()
+    )
+
+
+print("Top-cell name:", top_cell.name)
+print("From-cell prefix:", from_cell_name)
+print("Replacement-cell name:", replacement_cell.name)
+matches = 0
+replacements = 0
+
+for inst in top_cell.each_inst():
+    assert inst is not None
+
+    # Make sure we haven't already processed this gds
+    assert inst.cell.name != to_cell_name
+
+    # For cells that have no hierarchy beneath (standard cells in this case)
+    if inst.cell.hierarchy_levels() == 0 and inst.cell.name == from_cell_name:
+        assert cell_dimensions_equal(inst.cell, replacement_cell)
+        matches += 1
+
+        if random() < probability:
+            continue
+
+        inst.cell = replacement_cell
+        replacements += 1
+
+print(f"Replaced {replacements} cells out of {matches} matches.")
+print(f"Writing to {output_gds}...")
+
+user_layout.write(output_gds)
+print("Done.")