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Improved VBL handler installation check.

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Check hibyte of old handler in case it happens to be placed on a page boundary (+ minor beautifications).
This commit is contained in:
Oliver Schmidt 2015-08-28 14:42:29 +02:00
parent da593744f4
commit 8960e0bebb
1 changed files with 5 additions and 5 deletions
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10
drivers/vic20timer.s
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@ -34,7 +34,7 @@ old_handler:
; inputs: none
; outputs: none
timer_init:
lda old_handler
lda old_handler+1
bne @handler_installed
ldax IRQ_VECTOR
stax old_handler
@ -57,10 +57,11 @@ timer_read:
; tick over the current timer value - should be called 60 times per second
; inputs: none
; outputs: none (all registers preserved, by carry flag can be modified)
; outputs: none (all registers preserved, but carry flag can be modified)
timer_vbl_handler:
pha
lda #$11 ; 60 HZ =~ 17 ms per 'tick'
lda #17 ; 60 HZ =~ 17 ms per 'tick'
clc
adc current_time_value
sta current_time_value
bcc :+
@ -92,8 +93,7 @@ timer_vbl_handler:
: cmp #$5a
bne :+
lda #$00
:
sta current_seconds
: sta current_seconds
@done:
pla
jmp jmp_old_handler