From 92b5ee133abee25dff631c3955b80da221c02682 Mon Sep 17 00:00:00 2001
From: mc78 <mc78@outlook.de>
Date: Wed, 28 Aug 2024 13:07:00 +0200
Subject: [PATCH] Fixed imports and usage of deprecated vic and cia register
 names in set_viewport.s

---
 libsrc/c64/set_viewport.s | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/libsrc/c64/set_viewport.s b/libsrc/c64/set_viewport.s
index 48ca312d3..9d05120f2 100644
--- a/libsrc/c64/set_viewport.s
+++ b/libsrc/c64/set_viewport.s
@@ -1,44 +1,44 @@
 ;
-; Oliver Schmidt, 16.8.2018
+; Stefan 'MonteCarlos' Andree, 27.08.2024
 ;
 ; 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
-
+        .importzp       sp, tmp1, tmp2
+        .import         incsp1
+        .export         _set_viewport
 
 ;----------------------------------------------------------------------------
 .code
 
 .proc   _set_viewport
-        sta     tmp1     ; chr_hi
-        ldy     #0
+        ; on input, a contains chr_hi and stack contains scr_hi
+
+        sta     tmp1     ; save chr_hi for later
+        ldy     #0       ; scr_hi stack offset
         eor     (sp), y  ; eor scr_hi with chr_hi to determine VIC bank compliance
+        and     #$c0
         sec
         bne     @return  ; If the upper two bits do not coincide, then the screen and char would be in different VIC banks
-        
-        sty     tmp2     ; store bank bits temporarily, here      
-        lsr     tmp1     ; lsr hi-byte into correct bit position for VIC_ADDR (0x08 -> 0x02, 0x10 -> 0x04 ...)
+
+        sty     tmp2     ; store bank bits temporarily, here
+        lsr     tmp1     ; lsr hi-byte into correct bit position for VIC_VIDEO_ADR (0x08 -> 0x02, 0x10 -> 0x04 ...)
         lsr     tmp1     ; The vic bank check prevents doing this directly in an effective manner, beforehand
 
         lda     (sp), y  ; scr_hi
-        asl              ; rol hi-byte into correct bit position for VIC_ADDR (0x04 -> 0x10, 0x08 -> 0x20 ...)
+        asl              ; rol hi-byte into correct bit position for VIC_VIDEO_ADR (0x04 -> 0x10, 0x08 -> 0x20 ...)
         rol     tmp2     ; rol hi-bits into bank bits
         asl
-        rol     tmp2     ; rol's 0 into carry
+        rol     tmp2     ; rol's 0 into carry which results in returning EXIT_SUCCESS, later
         ora     tmp1     ; combine scr and char bits to the final register value
-        sta     VIC_ADDR
+        sta     VIC_VIDEO_ADR
 
-        lda     CIA2_pra
+        lda     CIA2_PRA
         ora     #$03     ; prepare for eor
         eor     tmp2     ; EOR bank bits, because in the register the bits are reversed
-        sta     CIA2_pra
+        sta     CIA2_PRA
     @return:
         jsr     incsp1   ; does not influence carry
         ; return EXIT_SUCCESS, if clc