pdn: connect the supply pins of dont_touch instances

flow/scripts/pdn.tcl

@@ -3,7 +3,21 @@ erase_non_stage_variables floorplan
 load_design 2_3_floorplan_tapcell.odb 2_1_floorplan.sdc
 source_step_tcl PRE PDN
 
+# A supply pin on no net changes no logic when it is connected: lift
+# dont_touch for the platform's global connections, restore it after.
+set lifted [dont_touch_unsupplied]
+foreach inst $lifted {
+  $inst setDoNotTouch 0
+}
 source $::env(PDN_TCL)
+foreach inst $lifted {
+  $inst setDoNotTouch 1
+}
+if { [llength $lifted] > 0 } {
+  utl::info FLW 18 "[llength $lifted] dont_touch instances had a supply pin\
+    on no net; connected by the global connections"
+}
+
 pdngen
 
 source_step_tcl POST PDN

flow/scripts/util.tcl

@@ -506,3 +506,25 @@ proc synth_verilog_files { } {
   }
   return $copies
 }
+
+# global_connect skips dont_touch instances (ODB-0383, a warning each),
+# so an instance made dont_touch before the PDN step keeps its supply
+# pins on no net: unpowered in the netlist, LVS and power analysis. The
+# dont_touch instances with a supply pin on no net, for the PDN step to
+# lift dont_touch from while it makes the global connections.
+proc dont_touch_unsupplied { } {
+  set insts {}
+  foreach inst [[ord::get_db_block] getInsts] {
+    if { ![$inst isDoNotTouch] } {
+      continue
+    }
+    foreach iterm [$inst getITerms] {
+      set type [[$iterm getMTerm] getSigType]
+      if { ($type eq "POWER" || $type eq "GROUND") && [$iterm getNet] eq "NULL" } {
+        lappend insts $inst
+        break
+      }
+    }
+  }
+  return $insts
+}

flow/test/test_pdn_dont_touch_supplies.py

@@ -0,0 +1,116 @@
+#!/usr/bin/env python3
+"""The PDN step connects the supply pins of dont_touch instances.
+
+global_connect skips a dont_touch instance, so an instance made
+dont_touch before the PDN step kept its supply pins on no net.
+dont_touch_unsupplied (util.tcl) names those instances, the PDN step
+lifts dont_touch from them for the global connections and restores it
+after; an instance whose supply pins are already on a net, or that is
+not dont_touch, is not named.
+
+Skipped when no openroad is available: OPENROAD_EXE or openroad on PATH.
+"""
+
+import os
+import shutil
+import subprocess
+import tempfile
+import unittest
+
+FLOW = os.path.join(os.path.dirname(os.path.abspath(__file__)), "..")
+UTIL_TCL = os.path.join(FLOW, "scripts", "util.tcl")
+LEF = os.path.join(FLOW, "platforms", "nangate45", "lef")
+
+DESIGN = """\
+module top (input a, output y0, output y1, output y2);
+  INV_X1 kept (.A(a), .ZN(y0));
+  INV_X1 free (.A(a), .ZN(y1));
+  INV_X1 supplied (.A(a), .ZN(y2));
+endmodule
+"""
+
+SETUP = f"""\
+set ::env(REPORTS_DIR) [pwd]
+source {{{UTIL_TCL}}}
+read_lef {{{os.path.join(LEF, "NangateOpenCellLibrary.tech.lef")}}}
+read_lef {{{os.path.join(LEF, "NangateOpenCellLibrary.macro.mod.lef")}}}
+read_verilog top.v
+link_design top
+set block [ord::get_db_block]
+proc supply_net {{ name }} {{
+  set net [[[ord::get_db_block] findInst $name] findITerm VDD]
+  set net [$net getNet]
+  if {{ $net eq "NULL" }} {{
+    return none
+  }}
+  return [$net getName]
+}}
+foreach pin {{VDD VSS}} {{
+  [[$block findInst supplied] findITerm $pin] connect \\
+    [odb::dbNet_create $block supplied_[string tolower $pin]]
+}}
+[$block findInst supplied] setDoNotTouch 1
+[$block findInst kept] setDoNotTouch 1
+"""
+
+# The platform's PDN script: add_global_connection connects at once.
+GLOBAL_CONNECTIONS = """\
+add_global_connection -net VDD -pin_pattern {^VDD$} -power
+add_global_connection -net VSS -pin_pattern {^VSS$} -ground
+global_connect
+"""
+
+
+def openroad_command():
+    openroad = os.environ.get("OPENROAD_EXE") or shutil.which("openroad")
+    return [openroad, "-no_init", "-no_splash", "-exit"] if openroad else None
+
+
+class TestPdnDontTouchSupplies(unittest.TestCase):
+    def run_openroad(self, body):
+        cmd = openroad_command()
+        if cmd is None:
+            self.skipTest("no openroad")
+        with tempfile.TemporaryDirectory() as tmp:
+            with open(os.path.join(tmp, "top.v"), "w") as f:
+                f.write(DESIGN)
+            with open(os.path.join(tmp, "test.tcl"), "w") as f:
+                f.write(SETUP + body)
+            result = subprocess.run(
+                cmd + ["test.tcl"], cwd=tmp, capture_output=True, text=True
+            )
+        output = result.stdout + result.stderr
+        self.assertEqual(result.returncode, 0, output)
+        return output
+
+    def test_global_connect_skips_dont_touch(self):
+        # The problem the PDN step works around, so this test notices
+        # when global_connect stops skipping dont_touch instances.
+        output = self.run_openroad(
+            GLOBAL_CONNECTIONS
+            + 'puts "kept=[supply_net kept] free=[supply_net free]"\n'
+        )
+        self.assertIn("kept=none free=VDD", output)
+
+    def test_names_only_unsupplied_dont_touch(self):
+        output = self.run_openroad(
+            'puts "lifted=[lmap i [dont_touch_unsupplied] { $i getName }]"\n'
+        )
+        self.assertIn("lifted=kept\n", output)
+
+    def test_lifted_for_global_connections(self):
+        # pdn.tcl's sequence around the platform's PDN script
+        output = self.run_openroad(
+            "set lifted [dont_touch_unsupplied]\n"
+            "foreach inst $lifted { $inst setDoNotTouch 0 }\n"
+            + GLOBAL_CONNECTIONS
+            + "foreach inst $lifted { $inst setDoNotTouch 1 }\n"
+            'puts "kept=[supply_net kept] supplied=[supply_net supplied]"\n'
+            'puts "dont_touch=[[$block findInst kept] isDoNotTouch]"\n'
+        )
+        self.assertIn("kept=VDD supplied=supplied_vdd", output)
+        self.assertIn("dont_touch=1", output)
+
+
+if __name__ == "__main__":
+    unittest.main()