sim: fix zero encoding

diff --git a/migen/sim/ipc.py b/migen/sim/ipc.py
index 5d9f9eb685ea2647cfc50cdb953ea2349548322e..f463dcfff706225c3a82e0e50c745b621241eb10 100644 (file)
--- a/migen/sim/ipc.py
+++ b/migen/sim/ipc.py
@@ -51,11 +51,14 @@ message_classes = [MessageTick, MessageGo, MessageWrite, MessageRead, MessageRea
 #
 
 def _pack_int(v):
-       p = []
-       while v != 0:
-               p.append(v & 0xff)
-               v >>= 8
-       p.insert(0, len(p))
+       if v == 0:
+               p = [1, 0]
+       else:
+               p = []
+               while v != 0:
+                       p.append(v & 0xff)
+                       v >>= 8
+               p.insert(0, len(p))
        return p
 
 def _pack_str(v):