dos33fsprogs/games/peasant/vblank.s
2022-03-01 00:34:48 -05:00

22 lines
524 B
ArmAsm

; wait for VBLANK
; no way to do this on II/II+ short of vapor lock / floating bus
; IIe you can read $C019 (in VBLANK when top bit 0)
; IIc you can also read $C019 (also can setup interrupt)
; IIgs you can read $C019 but reverse of IIe (in VBLANK when top bit 1)
VBLANK = $C019 ;
; wait for vblank on IIe
; positive? during vblank
wait_vblank_iie:
lda VBLANK
bmi wait_vblank_iie ; wait for positive (in vblank)
wait_vblank_done_iie:
lda VBLANK ; wait for negative (vlank done)
bpl wait_vblank_done_iie
rts