From 7cb879d1108267ce7bccf752a8236bad86e0289f Mon Sep 17 00:00:00 2001
From: Brion Vibber <brion@pobox.com>
Date: Sun, 22 Jan 2023 05:54:50 -0800
Subject: [PATCH] fix graphics set

forgot that the OS copies shadow registers over lol
---
 mandel.s | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/mandel.s b/mandel.s
index b5c5953..25eaffd 100644
--- a/mandel.s
+++ b/mandel.s
@@ -40,6 +40,10 @@ DMACTL = $D400
 DLISTL = $D402
 DLISTH = $D403
 
+; OS shadow registers
+SDLSTL = $230
+SDLSTH = $231
+
 .data
 
 aspect:
@@ -74,6 +78,10 @@ display_list:
         .byte $70 ; 8 blank lines
     .endrep
 
+    ; 8 scan lines, 1 row of 40-column text
+    .byte $42
+    .addr textbuffer
+
     ; 184 lines graphics
     ; ANTIC mode e (160px 2bpp, 1 scan line per line)
     .byte $4e
@@ -87,10 +95,6 @@ display_list:
         .byte $0e
     .endrep
 
-    ; 1 line 40-column text
-    .byte $42
-    .addr textbuffer
-
     .byte $41 ; jump and blank
     .addr display_list
 
@@ -474,14 +478,15 @@ enough:
     sta zoom
 
     ; Disable display DMA
-    lda #$00
     sta DMACTL
 
     ; Set up the display list
     lda #.lobyte(display_list)
-    sta DLISTL
+    sta DLISTL ; actual register
+    sta SDLSTL ; shadow register the OS will copy in
     lda #.hibyte(display_list)
-    sta DLISTH
+    sta DLISTH ; actual register
+    sta SDLSTH ; shadow register the OS will copy in
 
     ; zero the range from framebuffer_top to framebuffer_end
     lda #.lobyte(framebuffer_top)