194 lines
12 KiB
NASM
194 lines
12 KiB
NASM
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.include "consts.inc"
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.include "header.inc"
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.include "reset.inc"
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.include "utils.inc"
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.segment "ZEROPAGE"
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Frame: .res 1 ; Reserve 1 byte to store the number of frames
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Clock60: .res 1 ; Reserve 1 byte to store a counter that increments every second (60 frames)
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BgPtr: .res 2 ; Reserve 2 bytes (16 bits) to store a pointer to the background address
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; (we store first the lo-byte, and immediately after, the hi-byte) - little endian
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; PRG-ROM code located at $8000
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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.segment "CODE"
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Subroutine to load all 32 color palette values from ROM
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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.proc LoadPalette
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PPU_SETADDR $3F00
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ldy #0 ; Y = 0
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: lda PaletteData,y ; Lookup byte in ROM
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sta PPU_DATA ; Set value to send to PPU_DATA
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iny ; Y++
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cpy #32 ; Is Y equal to 32?
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bne :- ; Not yet, keep looping
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rts ; Return from subroutine
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.endproc
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Subroutine to load tiles and attributes into the first nametable
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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.proc LoadBackground
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lda #<BackgroundData ; Fetch the lo-byte of BackgroundData address
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sta BgPtr
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lda #>BackgroundData ; Fetch the hi-byte of BackgroundData address
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sta BgPtr+1
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PPU_SETADDR $2000
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ldx #$00 ; X = 0 --> x is the outer loop index (hi-byte) from $0 to $4
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ldy #$00 ; Y = 0 --> y is the inner loop index (lo-byte) from $0 to $FF
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OuterLoop:
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InnerLoop:
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lda (BgPtr),y ; Fetch the value *pointed* by BgPtr + Y
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sta PPU_DATA ; Store in the PPU data
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iny ; Y++
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cpy #0 ; If Y == 0 (wrapped around 256 times)?
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beq IncreaseHiByte ; Then: we need to increase the hi-byte
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jmp InnerLoop ; Else: Continue with the inner loop
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IncreaseHiByte:
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inc BgPtr+1 ; We increment the hi-byte pointer to point to the next background section (next 255-chunk)
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inx ; X++
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cpx #4 ; Compare X with #4
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bne OuterLoop ; If X is still not 4, then we keep looping back to the outer loop
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rts ; Return from subroutine
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.endproc
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Subroutine to load text in the nametable until it finds a 0-terminator
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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.proc LoadText
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;; TODO:
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;; Loop all characters from ROM and load/display the text in the nametable.
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;; Bonus points if you code manages to display an empty tile for [space].
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rts ; Return from subroutine
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.endproc
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Reset handler (called when the NES resets or powers on)
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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Reset:
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INIT_NES ; Macro to initialize the NES to a known state
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lda #0
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sta Frame ; Frame = 0
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sta Clock60 ; Clock60 = 0
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Main:
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jsr LoadPalette ; Call LoadPalette subroutine to load 32 colors into our palette
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jsr LoadBackground ; Call LoadBackground subroutine to load a full nametable of tiles and attributes
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jsr LoadText ; Call LoadText subroutine to draw the text message on the nametable
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EnablePPURendering:
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lda #%10010000 ; Enable NMI and set background to use the 2nd pattern table (at $1000)
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sta PPU_CTRL
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lda #0
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sta PPU_SCROLL ; Disable scroll in X
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sta PPU_SCROLL ; Disable scroll in Y
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lda #%00011110
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sta PPU_MASK ; Set PPU_MASK bits to render the background
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LoopForever:
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jmp LoopForever ; Force an infinite execution loop
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; NMI interrupt handler
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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NMI:
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inc Frame ; Frame++
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lda Frame ; Increment Clock60 every time we reach 60 frames (NTSC = 60Hz)
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cmp #60 ; Is Frame equal to #60?
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bne :+ ; If not, bypass Clock60 increment
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inc Clock60 ; But if it is 60, then increment Clock60 and zero Frame counter
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lda #0
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sta Frame
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:
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rti ; Return from interrupt
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; IRQ interrupt handler
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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IRQ:
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rti ; Return from interrupt
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Hardcoded list of color values in ROM to be loaded by the PPU
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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PaletteData:
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.byte $22,$29,$1A,$0F, $22,$36,$17,$0F, $22,$30,$21,$0F, $22,$27,$17,$0F ; Background palette
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.byte $22,$16,$27,$18, $22,$1A,$30,$27, $22,$16,$30,$27, $22,$0F,$36,$17 ; Sprite palette
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Background data with tile numbers that must be copied to the nametable
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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BackgroundData:
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$36,$37,$36,$37,$36,$37,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$35,$25,$25,$25,$25,$25,$25,$38,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$36,$37,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$39,$3A,$3B,$3A,$3B,$3A,$3B,$3C,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$35,$25,$25,$38,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$39,$3A,$3B,$3C,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$53,$54,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$55,$56,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$53,$54,$24,$24,$24,$24,$24,$24,$24,$24,$45,$45,$53,$54,$45,$45,$53,$54,$45,$45,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$55,$56,$24,$24,$24,$24,$24,$24,$24,$24,$47,$47,$55,$56,$47,$47,$55,$56,$47,$47,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$60,$61,$62,$63,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$24,$31,$32,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$24,$64,$65,$66,$67,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$24,$30,$26,$34,$33,$24,$24,$24,$24,$36,$37,$36,$37,$24,$24,$24,$24,$24,$24,$24,$68,$69,$26,$6A,$24,$24,$24,$24
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.byte $24,$24,$24,$24,$30,$26,$26,$26,$26,$33,$24,$24,$35,$25,$25,$25,$25,$38,$24,$24,$24,$24,$24,$24,$68,$69,$26,$6A,$24,$24,$24,$24
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.byte $B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5
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.byte $B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7
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.byte $B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B6
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.byte $B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7
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.byte $B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5,$B4,$B5
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.byte $B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7,$B6,$B7
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Attributes tell which palette is used by a group of tiles in the nametable
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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AttributeData:
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.byte %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000
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.byte %00000000, %10101010, %10101010, %00000000, %00000000, %00000000, %10101010, %00000000
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.byte %00000000, %00000000, %00000000, %00000000, %11111111, %00000000, %00000000, %00000000
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.byte %00000000, %00000000, %10101010, %10101010, %10101010, %10101010, %00000000, %00000000
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.byte %11111111, %00000000, %00000000, %00001111, %00001111, %00000011, %00000000, %00000000
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.byte %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000, %00000000
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.byte %11111111, %11111111, %11111111, %11111111, %11111111, %11111111, %11111111, %11111111
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.byte %11111111, %11111111, %11111111, %11111111, %11111111, %11111111, %11111111, %11111111
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Hardcoded ASCII message stored in ROM with 0-terminator
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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TextMessage:
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.byte "HELLO WORLD",$0
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Here we add the CHR-ROM data, included from an external .CHR file
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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.segment "CHARS"
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.incbin "mario.chr"
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;; Vectors with the addresses of the handlers that we always add at $FFFA
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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.segment "VECTORS"
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.word NMI ; Address (2 bytes) of the NMI handler
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.word Reset ; Address (2 bytes) of the Reset handler
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.word IRQ ; Address (2 bytes) of the IRQ handler
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