From a435792828e3114844e68fae09d7453a5f447ea7 Mon Sep 17 00:00:00 2001
From: gatecat <gatecat@ds0.me>
Date: Tue, 11 Aug 2026 13:43:31 +0200
Subject: [PATCH] nexus: Disconnect CCU2 CIN when it's a don't care

Signed-off-by: gatecat <gatecat@ds0.me>
---
 nexus/pack.cc | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/nexus/pack.cc b/nexus/pack.cc
index 0768afaf..aba45e21 100644
--- a/nexus/pack.cc
+++ b/nexus/pack.cc
@@ -1602,6 +1602,12 @@ struct NexusPacker
             CellInfo *ci = cell.second.get();
             if (ci->type != id_CCU2)
                 continue;
+
+            // For CCU2s with LUT value 0xFFFF, CIN is a don't-care
+            // disconnect it so it doesn't cause an error below or during chaining
+            if (str_or_default(ci->params, id_INIT0, "") == "0xFFFF")
+                ci->disconnectPort(id_CIN);
+
             NetInfo *cin = ci->getPort(id_CIN);
             if (cin) {
                 if (cin->driver.cell && cin->driver.cell->type != id_CCU2) {