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cc65/libsrc/apple2/waitvsync.s

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ArmAsm
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;
; Oliver Schmidt, 2020-06-14
;
; void waitvsync (void);
;
.ifdef __APPLE2ENH__
.constructor initvsync
.export _waitvsync
.import _get_ostype
.include "apple2.inc"
.segment "ONCE"
initvsync:
jsr _get_ostype
sta ostype
rts
.code
_waitvsync:
bit ostype
bmi iigs ; $8x
bvs iic ; $4x
: bit RDVBLBAR
bpl :- ; Blanking
: bit RDVBLBAR
bmi :- ; Drawing
rts
; Apple IIgs TechNote #40, VBL Signal
iigs: bit RDVBLBAR
bmi iigs ; Blanking
: bit RDVBLBAR
bpl :- ; Drawing
rts
; Apple IIc TechNote #9, Detecting VBL
iic: sei
sta IOUDISOFF
lda RDVBLMSK
bit ENVBL
bit PTRIG ; Reset VBL interrupt flag
: bit RDVBLBAR
bpl :-
asl
bcs :+ ; VBL interrupts were already enabled
bit DISVBL
: sta IOUDISON ; IIc Tech Ref Man: The firmware normally leaves IOUDIS on.
cli
rts
.segment "INIT"
ostype: .res 1
.endif ; __APPLE2ENH__