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atrtimer.s: initialize the interrupt variables before enabling the interrupt
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@ -27,19 +27,12 @@ vbichain: .word 0
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.code
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; reset timer to 0
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; reset timer to 0 and install handler
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; inputs: none
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; outputs: none
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timer_init:
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lda vbichain+1
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bne @handler_installed
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ldax VVBLKI ; IMMEDIATE VERTICAL BLANK NMI VECTOR
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stax vbichain ; save old immediate vector
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ldy #<timer_vbl_handler
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ldx #>timer_vbl_handler
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lda #6 ; STAGE 1 VBI
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jsr SETVBV ; vector to set VBLANK parameters
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@handler_installed:
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bne @done
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lda PAL ; hardware register describing TV system of GTIA
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and #$0e ; mask out irrelevant bits
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bne @ntsc
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@ -56,11 +49,18 @@ timer_init:
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lda #17
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sta timer_freq_reciproc
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@system_set:
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lda #0
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lda #0 ; initialize time variables
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sta current_time_value
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sta current_time_value+1
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sta current_seconds
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sta current_jiffies
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ldax VVBLKI ; IMMEDIATE VERTICAL BLANK NMI VECTOR
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stax vbichain ; save old immediate vector
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ldy #<timer_vbl_handler
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ldx #>timer_vbl_handler
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lda #6 ; STAGE 1 VBI
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jsr SETVBV ; vector to set VBLANK parameters
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@done:
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rts
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timer_exit:
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