Added function to set viewport

2025-01-21 15:32:41 +00:00 · 2024-08-27 14:17:23 +02:00 · 2024-08-27 14:17:23 +02:00 · 5e530526ba
commit 5e530526ba
parent f84f3ff0dc
1 changed files with 39 additions and 0 deletions
--- a/libsrc/c64/set_viewport.s
+++ b/libsrc/c64/set_viewport.s
@ -0,0 +1,39 @@
+;
+; Oliver Schmidt, 16.8.2018
+;
+; int __fastcall__ set_viewport (uint8_t scr_hi, uint8_t chr_hi);
+;
+
+        .include        "time.inc"
+        .include        "c64.inc"
+
+        .importzp       sreg, ptr1
+        .import         pushax, pusheax, ldax0sp, ldeaxidx
+        .import         tosdiveax, incsp3, return0
+        .import         TM, load_tenth
+
+
+;----------------------------------------------------------------------------
+.code
+
+.proc   _set_viewport
+        lsr
+        lsr
+        sta tmp1    ; chr_hi
+        lda #0
+        sta tmp2    ; bank
+        jsr popa    ; scr_hi
+        asl
+        rol tmp2
+        asl
+        rol tmp2
+        ora tmp1
+        sta VIC_ADDR
+
+        lda CIA2_pra
+        ora #$03
+        eor tmp2
+        sta CIA2_pra
+
+        rts
+.endproc