From 0fd4a706001a3fa862fa24f9babd712217e44a18 Mon Sep 17 00:00:00 2001
From: folkert van heusden <mail@vanheusden.com>
Date: Thu, 23 Mar 2023 22:09:19 +0100
Subject: [PATCH] for some reason unixv5 wants to write a word to the system id
 i/o address

---
 bus.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/bus.cpp b/bus.cpp
index 330df5a..4e8630f 100644
--- a/bus.cpp
+++ b/bus.cpp
@@ -867,6 +867,9 @@ void bus::write(const uint16_t a, const bool word_mode, uint16_t value, const bo
 		if (a == ADDR_SYSSIZE || a == ADDR_SYSSIZE + 2)  // system size (is read-only)
 			return;
 
+		if (a == ADDR_SYSTEM_ID)  // is r/o
+			return;
+
 		///////////
 
 		DOLOG(debug, true, "UNHANDLED write %o(%c): %o", a, word_mode ? 'B' : 'W', value);