timing - Who's calling my interrupt handler if I have both CIAs turned off? -
i'm trying set simple raster interrupt handler change background color in given stripe. however, interrupt handler seems called time. (the code uses ca65's format)
.include "c64.inc" row = 100 .segment "zpsave" .segment "startup" sei ;; turn off basic , kernal rom lda #$35 sta $01 ;; flush cia irqs bit cia1_icr bit cia2_icr ;; turn off cia interrupts lda #%011111111 sta cia1_icr sta cia2_icr ;; set target raster line lda #%01111111 , vic_ctrl1 sta vic_ctrl1 lda #row sta vic_hline ;; enable vic interrupt lda #%00000001 sta vic_imr ;; install interrupt handler lda #<isr sta $fffe lda #>isr sta $ffff cli rts .macro isr_pre pha txa pha tya pha .endmacro .macro isr_post pla tay pla tax rti .endmacro ;;; acknowledge vic interrupt .macro ack_vic lda vic_irr , #$01 sta vic_irr .endmacro .proc isr isr_pre ack_vic ;; uncommenting these lines works around problem ;; lda vic_hline ;; cmp #row ;; bne exit lda #1 sta vic_bordercolor sta vic_bg_color0 ldx #50 : dex bne :- lda #0 sta vic_bordercolor sta vic_bg_color0 exit: isr_post .endproc if comment out 3 lines marked "workaround" in above code, interrupt handler called time, not on (the start of) row row:
if uncomment 3 lines, works, it's unstable, guess because of same unintended interrupts:
i've found several problems code posted above, , fixing of them fixed problem:
- the bitmask turning off
ciainterrupts wrong (it accidentally 9 bits long) -- causing interrupt firings... - the
isrpostscriptum macro missingplarestorearegister -- screwed state royally, whatever happened old code more-or-less chance... - the
vicinterrupt not flushed in interrupt setup code -- after fixing previous 2 problems, interrupts never triggered. - there's nothing
rts@ end of setup code, since turn off kernal , basic rom
so fixed code follows:
.include "c64.inc" row = 100 ;;; acknowledge vic interrupt .macro ack_vic lda vic_irr , #$01 sta vic_irr .endmacro .segment "zpsave" .segment "startup" sei ;; turn off basic , kernal rom lda #$35 sta $01 ;; flush cia irqs bit cia1_icr bit cia2_icr ack_vic ;; turn off cia interrupts lda #%01111111 sta cia1_icr sta cia2_icr ;; set target raster line lda #%01111111 , vic_ctrl1 sta vic_ctrl1 lda #row sta vic_hline ;; enable vic interrupt lda #%00000001 sta vic_imr ;; install interrupt handler lda #<isr sta $fffe lda #>isr sta $ffff cli jmp * .macro isr_pre pha txa pha tya pha .endmacro .macro isr_post pla tay pla tax pla rti .endmacro .proc isr isr_pre ack_vic lda #1 sta vic_bordercolor sta vic_bg_color0 ldx #50 : dex bne :- lda #0 sta vic_bordercolor sta vic_bg_color0 exit: isr_post .endproc this results, expected, in solid white stripe. unknown reason, stripe starts @ middle of screen horizontally, guess that'd 1 separate question.
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