From 9d9d36730223cb7a36fca425f6fc5bcbb43e7b02 Mon Sep 17 00:00:00 2001
From: Saqib Khan <11544614+saqibkh@users.noreply.github.com>
Date: Tue, 29 Sep 2026 06:50:57 -0600
Subject: [PATCH] Support waiting on clocking block event through modport
 (#8403) (#8530)

---
 docs/CONTRIBUTORS                             |  1 +
 src/V3LinkDot.cpp                             | 11 ++-
 .../t/t_mod_interface_clocking_event.py       | 18 +++++
 .../t/t_mod_interface_clocking_event.v        | 79 +++++++++++++++++++
 4 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100755 test_regress/t/t_mod_interface_clocking_event.py
 create mode 100644 test_regress/t/t_mod_interface_clocking_event.v

diff --git a/docs/CONTRIBUTORS b/docs/CONTRIBUTORS
index 715feab24..f1efe8a20 100644
--- a/docs/CONTRIBUTORS
+++ b/docs/CONTRIBUTORS
@@ -294,6 +294,7 @@ Ryan Ziegler
 Ryszard Rozak
 Saksham Gupta
 Samuel Riedel
+Saqib Khan
 Sean Cross
 Sebastien Van Cauwenberghe
 Secturion
diff --git a/src/V3LinkDot.cpp b/src/V3LinkDot.cpp
index 8ef4bda56..b8244eae3 100644
--- a/src/V3LinkDot.cpp
+++ b/src/V3LinkDot.cpp
@@ -3482,6 +3482,13 @@ class LinkDotResolveVisitor final : public VNVisitor {
         }
         defParamPins.emplace(nodep->paramPath(), nodep);
     }
+    static AstClocking* sensClockingp(AstNode* nodep) {
+        // Return the clocking block referenced by nodep, either directly or through a modport
+        if (AstClocking* const clockingp = VN_CAST(nodep, Clocking)) return clockingp;
+        if (const AstModportClockingRef* const clockingRefp = VN_CAST(nodep, ModportClockingRef))
+            return clockingRefp->clockingp();
+        return nullptr;
+    }
     VSymEnt* getCreateClockingEventSymEnt(AstClocking* clockingp) {
         AstVar* const eventp = clockingp->ensureEventp(true);
         if (!eventp->user1p()) eventp->user1p(new VSymEnt{m_statep->symsp(), eventp});
@@ -4465,7 +4472,7 @@ class LinkDotResolveVisitor final : public VNVisitor {
             bool ok = false;
             // Special case: waiting on clocking event
             if (m_inSens && foundp && m_ds.m_dotPos != DP_SCOPE && m_ds.m_dotPos != DP_FIRST) {
-                if (AstClocking* const clockingp = VN_CAST(foundp->nodep(), Clocking)) {
+                if (AstClocking* const clockingp = sensClockingp(foundp->nodep())) {
                     foundp = getCreateClockingEventSymEnt(clockingp);
                 }
             }
@@ -5081,7 +5088,7 @@ class LinkDotResolveVisitor final : public VNVisitor {
                     foundp = m_statep->findSymPrefixed(dotSymp, nodep->name(), baddot, true);
                 }
                 if (m_inSens && foundp) {
-                    if (AstClocking* const clockingp = VN_CAST(foundp->nodep(), Clocking)) {
+                    if (AstClocking* const clockingp = sensClockingp(foundp->nodep())) {
                         foundp = getCreateClockingEventSymEnt(clockingp);
                     }
                 }
diff --git a/test_regress/t/t_mod_interface_clocking_event.py b/test_regress/t/t_mod_interface_clocking_event.py
new file mode 100755
index 000000000..6fe7d000c
--- /dev/null
+++ b/test_regress/t/t_mod_interface_clocking_event.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# This program is free software; you can redistribute it and/or modify it
+# under the terms of either the GNU Lesser General Public License Version 3
+# or the Perl Artistic License Version 2.0.
+# SPDX-FileCopyrightText: 2026 Wilson Snyder
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('simulator')
+
+test.compile(verilator_flags2=["--binary"])
+
+test.execute()
+
+test.passes()
diff --git a/test_regress/t/t_mod_interface_clocking_event.v b/test_regress/t/t_mod_interface_clocking_event.v
new file mode 100644
index 000000000..97c8770c7
--- /dev/null
+++ b/test_regress/t/t_mod_interface_clocking_event.v
@@ -0,0 +1,79 @@
+// DESCRIPTION: Verilator: Verilog Test module
+//
+// This file ONLY is placed under the Creative Commons Public Domain
+// SPDX-FileCopyrightText: 2026 Saqib Khan
+// SPDX-License-Identifier: CC0-1.0
+
+// Wait on a clocking block event through a modport (#8403)
+
+// verilog_format: off
+`define stop $stop
+`define checkd(gotv,expv) do if ((gotv) !== (expv)) begin $write("%%Error: %s:%0d:  got=%0d exp=%0d\n", `__FILE__,`__LINE__, (gotv), (expv)); `stop; end while(0);
+// verilog_format: on
+
+`timescale 1ns / 1ns
+
+interface simple_if (
+    input logic clk
+);
+  logic req;
+  clocking mem_cb @(posedge clk);
+    output req;
+  endclocking
+  clocking mon_cb @(negedge clk);
+    input req;
+  endclocking
+  modport mem_mp(clocking mem_cb);
+  modport mon_mp(clocking mon_cb);
+endinterface
+
+module via_mp (
+    simple_if.mem_mp p,
+    simple_if.mon_mp m
+);
+  int mem_count = 0;
+  int mon_count = 0;
+
+  task automatic wait_mon();
+    @(m.mon_cb);
+  endtask
+
+  initial begin
+    repeat (3) begin
+      @(p.mem_cb);
+      mem_count++;
+      $display("[%0t] mem_cb %0d", $time, mem_count);
+    end
+    p.mem_cb.req <= 1'b1;
+  end
+
+  initial begin
+    repeat (3) begin
+      wait_mon();
+      mon_count++;
+      $display("[%0t] mon_cb %0d", $time, mon_count);
+    end
+  end
+endmodule
+
+module t;
+  logic clk = 0;
+  always #5 clk = ~clk;
+
+  simple_if intf (.clk(clk));
+  initial intf.req = 1'b0;
+
+  via_mp u (
+      .p(intf.mem_mp),
+      .m(intf.mon_mp)
+  );
+
+  initial begin
+    #100;
+    `checkd(u.mem_count, 3);
+    `checkd(u.mon_count, 3);
+    `checkd(intf.req, 1'b1);
+    $write("*-* All Finished *-*\n");
+    $finish;
+  end
+endmodule