mirror of https://github.com/safiire/n65.git
214 lines
3.2 KiB
NASM
214 lines
3.2 KiB
NASM
;;;;
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; Create an iNES header
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.ines {"prog": 1, "char": 0, "mapper": 0, "mirror": 0}
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;;;;
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; Include all the symbols in the nes library
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.inc <nes.sym>
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;;;;
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; Open the prog section bank 0
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.segment prog 0
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;;;;
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; Structure to keep track of input
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.org $0000
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.scope controller_state
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.space b 1
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.space a 1
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.
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;;;;
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; Setup the interrupt vectors
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.org $FFFA
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.dw vblank
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.dw reset
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.dw irq
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;;;;
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; Here is our code entry point
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.org $C000
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.scope reset
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sei ; SEt Interrupt (Disables them)
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cld ; CLear Decimal Mode
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ldx #$ff
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txs ; Set the stack pointer
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ldx #$00
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stx nes.ppu.control
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stx nes.ppu.mask ; Disable Vblank & Rendering
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jsr zero_apu ; Zero all APU registers
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; We need to wait for at least 2 Vblanks to happen
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; before we know the PPU has stabilized at startup
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; Here we wait for the first one.
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wait_vblank1:
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bit nes.ppu.status
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bpl wait_vblank1
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; Before we wait for the second vblank, lets
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; zero all of the working RAM $0 to $800
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; The $200s are sprite OAM, and should be set to $ff
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clear_ram:
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lda #$00
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sta $00, x
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sta $100, x
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sta $300, x
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sta $400, x
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sta $500, x
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sta $600, x
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sta $700, x
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lda #$ff
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sta $200, x
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inx
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bne clear_ram
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; Now wait for the second vblank
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wait_vblank2:
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bit nes.ppu.status
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bpl wait_vblank2
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jsr initialize
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forever:
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jmp forever
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rti
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.
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;;;;
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; Initialize everything
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.scope initialize
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; Enable pulse1 and pulse2 in the APU
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lda #%00000011
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sta nes.apu.channel_enable
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; Initialize the controller states
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lda #$00
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sta controller_state.a zp
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sta controller_state.b zp
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; Reenable interrupts, Turn Vblank back on
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lda #%10000000
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sta nes.ppu.control
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cli
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rts
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.
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;;;;
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; VBlank is called 60 times per second
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.scope vblank
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jsr read_input
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rti
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.
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;;;;
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; IRQ, we are not using
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.scope irq
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rti
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.
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;;;;
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; Zero all the APU registers
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.scope zero_apu
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lda #$00
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ldx #$00
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loop:
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sta $4000, x
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inx
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cpx $18
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bne loop
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rts
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.
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;;;;
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; Read input from controller 1
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.scope read_input
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lda #$01 ; strobe joypad
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sta nes.controller1
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lda #$00
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sta nes.controller1
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; Handle Button A
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lda nes.controller1
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and #$01
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beq update_a_state
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; A is pressed, but did it just change to being pressed now?
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ldx controller_state.a zp
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bne update_a_state
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; do the thing A does
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jsr play_e329
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update_a_state:
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sta controller_state.a zp
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; Handle Button B
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lda nes.controller1
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and #$01
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beq update_b_state
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; B is pressed, but did it just change to being pressed now?
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ldx controller_state.b zp
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bne update_b_state
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; Do the thing B does
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jsr play_a220
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update_b_state:
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sta controller_state.b zp
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rts
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.
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;;;;
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;; This will play an A 220hz note
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;; On the pulse1 generator
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.scope play_a220
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pha
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lda #%10011111
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sta nes.apu.pulse1.control
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lda #%11111011
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sta nes.apu.pulse1.ft
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lda #%11111001
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sta nes.apu.pulse1.ct
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pla
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rts
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.
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;;;;
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;; This will play an E 329.63hz note
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;; On the pulse2 generator
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.scope play_e329
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pha
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lda #%10011111
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sta nes.apu.pulse2.control
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lda #%01010010
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sta nes.apu.pulse2.ft
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lda #%11111001
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sta nes.apu.pulse2.ct
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pla
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rts
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.
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