From c46f2bbd86e73f9254051dabc573380a7dc157fd Mon Sep 17 00:00:00 2001
From: TG <tarik.graba@telecom-paris.fr>
Date: Tue, 2 Dec 2025 08:58:19 +0100
Subject: [PATCH] ice40: Explicitly connect CIN when legalizing carry chain

This connection is implicit as it is hardwired in the hardware.
This commit makes the connection explicit and thus appearing in the
generated netlist allowing post-rout simulation.
---
 ice40/chains.cc | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/ice40/chains.cc b/ice40/chains.cc
index f6e236a7..6af7eb3f 100644
--- a/ice40/chains.cc
+++ b/ice40/chains.cc
@@ -122,6 +122,8 @@ class ChainConstrainer
         o_r.cell = lc.get();
         cout_port.net->driver = o_r;
         cout_port.net = co_i3_net;
+        // CIN is connected to COUT in hardware, make the connection explicit in the netlist
+        lc->connectPort(id_CIN, co_i3_net);
 
         // If COUT also connects to a CIN; preserve the carry chain
         if (cin_cell) {