part 4

2 files changed, 197 insertions, 0 deletions

diff --git a/media/sprites.chr b/media/sprites.chr
new file mode 100644
index 0000000..3713c9c
--- /dev/null
+++ b/media/sprites.chr
diff --git a/media/sprites.s b/media/sprites.s
new file mode 100644
index 0000000..5f0b3d9
--- /dev/null
+++ b/media/sprites.s
@@ -0,0 +1,197 @@
+.ROMBANKMAP
+BANKSTOTAL  2
+BANKSIZE    $4000
+BANKS       1
+BANKSIZE    $2000
+BANKS       1
+.ENDRO
+
+.MEMORYMAP
+DEFAULTSLOT  0
+SLOTSIZE     $4000
+SLOT 0       $C000
+SLOTSIZE     $2000
+SLOT 1       $0000
+.ENDME
+
+.ENUM $00
+sleeping     DB
+.ENDE
+
+; just use the actual locations in our copy of SPR-RAM rather than zero-page
+; addresses, to avoid having to do multiple copies
+.define sprite_x  $0203
+.define sprite_y  $0200
+
+  .bank 0 slot 0
+  .org $0000
+RESET:
+  SEI
+  CLD
+  LDX #$FF
+  TXS
+  INX
+  STX $2000.w
+  STX $2001.w
+  STX $4010.w
+  LDX #$40
+  STX $4017.w
+
+vblankwait1:
+  BIT $2002
+  BPL vblankwait1
+
+clrmem:
+  LDA #$00
+  STA $0000, x
+  STA $0100, x
+  STA $0300, x
+  STA $0400, x
+  STA $0500, x
+  STA $0600, x
+  STA $0700, x
+  LDA #$FE
+  STA $0200, x
+  INX
+  BNE clrmem
+
+  ; start with the sprite near the middle of the screen
+  LDA #$80
+  STA sprite_x
+  STA sprite_y
+
+vblankwait2:
+  BIT $2002
+  BPL vblankwait2
+
+  ; PPU is initialized here, so we can start writing data into it. this is safe
+  ; because we have not yet enabled drawing, and so we don't have to restrain
+  ; ourselves to vblank.
+
+  ; first, we load the palettes into $3F00 and $3F10
+load_palettes:
+  LDA $2002    ; read here so that the next byte written to $2006 is the high
+  LDA #$3F     ; byte of the address
+  STA $2006    ; write the high byte of the base address
+  LDA #$00
+  STA $2006    ; write the low byte of the base address
+  LDX #$00
+load_palettes_loop:
+  LDA palette.w, x
+  STA $2007
+  INX
+  CPX #$20     ; 16 byte background palette plus 16 byte sprite palette
+  BNE load_palettes_loop
+
+  ; then we draw the background (doing that here because it won't be changing)
+  LDA #$20
+  STA $2006 ; high byte of the starting address
+  LDA #$00
+  STA $2006 ; low byte of the starting address
+  LDA #$01 ; pattern index 1 is our background tile
+  LDX #$04             ; this loop will load $2000-$23FF, which includes the
+  LDY #$00             ; attribute table range, but we can just adjust the
+load_background_loop:  ; palette to take that into account
+  STA $2007
+  INY
+  BNE load_background_loop
+  DEX
+  BNE load_background_loop
+
+  ; then we set the unchanging parts of our sprite (the pattern index and the
+  ; attributes)
+  LDA #$00
+  STA $0201 ; pattern index 0 is our sprite
+  STA $0202 ; don't need any attributes
+
+  ; enable the PPU
+  LDA #%10000000
+  STA $2000
+  LDA #%00011000
+  STA $2001
+
+loop:
+  INC sleeping
+wait_for_vblank_end:
+  LDA sleeping
+  BNE wait_for_vblank_end
+
+  LDA #$01
+  STA $4016
+  LDA #$00
+  STA $4016
+
+  ; we don't care about a, b, select, start
+  LDA $4016
+  LDA $4016
+  LDA $4016
+  LDA $4016
+
+up:
+  LDA $4016
+  AND #%00000001
+  BEQ down
+  LDX sprite_y.w
+  DEX
+  STX sprite_y.w
+down:
+  LDA $4016
+  AND #%00000001
+  BEQ left
+  LDX sprite_y.w
+  INX
+  STX sprite_y.w
+left:
+  LDA $4016
+  AND #%00000001
+  BEQ right
+  LDX sprite_x.w
+  DEX
+  STX sprite_x.w
+right:
+  LDA $4016
+  AND #%00000001
+  BEQ loop_end
+  LDX sprite_x.w
+  INX
+  STX sprite_x.w
+
+loop_end:
+  JMP loop
+
+NMI:
+  PHA
+  TXA
+  PHA
+  TYA
+  PHA
+
+  ; now the only thing we need to do here is issue a DMA call to transfer our
+  ; sprite data into SPR-RAM
+  LDA #$00
+  STA $2003 ; reset the SPR-RAM write offset
+  LDA #$02
+  STA $4014 ; start the DMA transfer from $0200
+
+  LDA #$00
+  STA sleeping
+  PLA
+  TAY
+  PLA
+  TAX
+  PLA
+
+  RTI
+
+palette:
+  .db $0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30
+  .db $0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30,$0F,$30
+
+  .orga $FFFA
+  .dw NMI
+  .dw RESET
+  .dw 0
+
+  .bank 1 slot 1
+  .org $0000
+  .incbin "sprites.chr"