 Re: How to use timer 2 and timer 3 interrupts with raster interrupts?
Timer 2 and 3 need to be reloaded after countdown.
Initialization:
sei
ldx CINV
ldy CINV+1
stx oldcinv
sty oldcinv+1
ldx #<userirqint
ldy #>userirqint
stx CINV
sty CINV+1
ldx #<period
ldy #>period
stx T3LO
sty T3HI
lda #<rasterline
sta RASTER
lda #[T3 | RAS | >rasterline]
sta IRQMSK
cli
Interrupt service routine:
userirqint:
lda #T3
and IRQCR
; and IRQMSK
beq ?skipt3
; ora #RAS
sta IRQCR
ldx #<period
ldy #>period
stx T3LO
sty T3HI
nop ;do something
pla
tay
pla
tax
pla
rti
?skipt3
lda #RAS
and IRQCR
; and IRQMSK
beq ?skipraster
; ora #T3
sta IRQCR
lda #<rasterline
sta RASTER
lda #[T3 | RAS | >rasterline]
sta IRQMSK
nop ;do something
?exit
pla
tay
pla
tax
pla
rti
?skipraster
jmp (oldcinv)
If T3 IRQ shouldn't disturb in RASTER routine then I'm enabling IRQ earlier and moving RASTER service prior to T3:
userirqint:
lda #T3
and IRQCR
; and IRQMSK
beq ?skipt3
; ora #RAS
sta IRQCR
ldx #<period
ldy #>period
stx T3LO
sty T3HI
cli
nop ;do something
pla
tay
pla
tax
pla
rti
?skipt3
Equates:
CINV = $314
T3LO = $FF04
T3HI = $FF05
T3 = 1 << 6
T2 = 1 << 4
T1 = 1 << 3
LP = 1 << 2
RAS = 1 << 1
IRQCR = $FF09
IRQMSK = $FF0A
RASTER = $FF0B
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