From 24d64bf788a1eb2c633f66de1b3e1d198b5c90f4 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 4 Jan 2024 11:17:20 -0500
Subject: [PATCH] ROM is never shadowed; also add `assert`.

---
 Machines/Apple/AppleIIgs/MemoryMap.hpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Machines/Apple/AppleIIgs/MemoryMap.hpp b/Machines/Apple/AppleIIgs/MemoryMap.hpp
index 92033f339..6d1820caf 100644
--- a/Machines/Apple/AppleIIgs/MemoryMap.hpp
+++ b/Machines/Apple/AppleIIgs/MemoryMap.hpp
@@ -70,6 +70,11 @@ class MemoryMap {
 		}
 
 		bool is_shadowed(const Region &region, uint32_t address) const {
+			// ROM is never shadowed.
+			if(!region.write) {
+				return false;
+			}
+
 			const auto physical = physical_address(region, address);
 			assert(physical >= 0 && physical <= 0xff'ffff);
 			return shadow_pages_[(physical >> 10) & 127] & shadow_banks_[physical >> 17];