From 404af7500c360724f3b3043a5301d321ff7d9ed2 Mon Sep 17 00:00:00 2001
From: mc78 <mc78@outlook.de>
Date: Mon, 26 Aug 2024 00:47:25 +0200
Subject: [PATCH] Added check that given screen addr hi is not between
 $1000-$1fff nor between $9000-$9fff due to shadowing

---
 libsrc/cbm/workingscreenaddr.s | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/libsrc/cbm/workingscreenaddr.s b/libsrc/cbm/workingscreenaddr.s
index a2780dce6..7c2d1f488 100644
--- a/libsrc/cbm/workingscreenaddr.s
+++ b/libsrc/cbm/workingscreenaddr.s
@@ -13,6 +13,16 @@ _cbm_set_working_screen:
         tax
         and #3
         bne @error
+        cpx #$10    ; Screen addr must not be set to $1000-$1fff nor $9000-$9fff
+        bcc @ok_1000
+        cpx #$1f
+        bcc @error
+    @ok_1000:
+        cpx #$90    ; Screen addr must not be set to $1000-$1fff nor $9000-$9fff
+        bcc @ok_9000
+        cpx #$9f
+        bcc @error
+    @ok_9000:
         stx SCREEN_HI
         sec
         jsr PLOT    ; Get cursor position ...