nesemu/tests/cpu_exec_space/source/common/ppu.s

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2023-12-03 00:27:07 -05:00
; PPU utilities
bss_res ppu_not_present
; Sets PPUADDR to w
; Preserved: X, Y
.macro set_ppuaddr w
bit PPUSTATUS
setb PPUADDR,>w
setb PPUADDR,<w
.endmacro
; Delays by no more than n scanlines
.macro delay_scanlines n
.if CLOCK_RATE <> 1789773
.error "Currently only supports NTSC"
.endif
delay ((n)*341)/3
.endmacro
; Waits for VBL then disables PPU rendering.
; Preserved: A, X, Y
disable_rendering:
pha
jsr wait_vbl_optional
setb PPUMASK,0
pla
rts
; Fills first nametable with $00
; Preserved: Y
clear_nametable:
ldx #$20
bne clear_nametable_
clear_nametable2:
ldx #$24
clear_nametable_:
lda #0
jsr fill_screen_
; Clear pattern table
ldx #64
: sta PPUDATA
dex
bne :-
rts
; Fills screen with tile A
; Preserved: A, Y
fill_screen:
ldx #$20
bne fill_screen_
; Same as fill_screen, but fills other nametable
fill_screen2:
ldx #$24
fill_screen_:
stx PPUADDR
ldx #$00
stx PPUADDR
ldx #240
: sta PPUDATA
sta PPUDATA
sta PPUDATA
sta PPUDATA
dex
bne :-
rts
; Fills palette with $0F
; Preserved: Y
clear_palette:
set_ppuaddr $3F00
ldx #$20
lda #$0F
: sta PPUDATA
dex
bne :-
; Fills OAM with $FF
; Preserved: Y
clear_oam:
lda #$FF
; Fills OAM with A
; Preserved: A, Y
fill_oam:
ldx #0
stx SPRADDR
: sta SPRDATA
dex
bne :-
rts
; Initializes wait_vbl_optional. Must be called before
; using it.
.align 32
init_wait_vbl:
; Wait for VBL flag to be set, or ~60000
; clocks (2 frames) to pass
ldy #24
ldx #1
bit PPUSTATUS
: bit PPUSTATUS
bmi @set
dex
bne :-
dey
bpl :-
@set:
; Be sure flag didn't stay set (in case
; PPUSTATUS always has high bit set)
tya
ora PPUSTATUS
sta ppu_not_present
rts
; Same as wait_vbl, but returns immediately if PPU
; isn't working or doesn't support VBL flag
; Preserved: A, X, Y
.align 16
wait_vbl_optional:
bit ppu_not_present
bmi :++
; FALL THROUGH
; Clears VBL flag then waits for it to be set.
; Preserved: A, X, Y
wait_vbl:
bit PPUSTATUS
: bit PPUSTATUS
bpl :-
: rts