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Fixed imports and usage of deprecated vic and cia register names in set_viewport.s

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mc78 2024-08-28 13:07:00 +02:00
parent cb0862d01b
commit 92b5ee133a
1 changed files with 17 additions and 17 deletions
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34
libsrc/c64/set_viewport.s
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@ -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