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ds: move to 60Hz interrupt

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This commit is contained in:
Vince Weaver 2019-10-02 23:25:08 -04:00
parent a07f0d8f2e
commit fbd613486d
1 changed files with 9 additions and 4 deletions
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13
demosplash/pt3_lib_mockingboard.s
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@ -297,8 +297,10 @@ done_apple_detect:
sta $03ff
;============================
; Enable 50Hz clock on 6522
; Enable 60Hz clock on 6522
;============================
; yes this is horrible for PT3 files
; but in our case we are matching the screen refresh
sei ; disable interrupts just in case
@ -311,14 +313,17 @@ done_apple_detect:
sta $C40D ; IFR: 1100, enable interrupt on timer one oflow
sta $C40E ; IER: 1100, enable timer one interrupt
lda #$E7
lda #$1A
sta $C404 ; write into low-order latch
lda #$4f
lda #$41
sta $C405 ; write into high-order latch,
; load both values into counter
; clear interrupt and start counting
; 4fe7 / 1e6 = .020s, 50Hz
; 9c40 / 1e6 = .040s, 25Hz
; 4fe7 / 1e6 = .020s, 50Hz
; 411a / 1e6 = .016s, 60Hz
rts