Engine.6502

	.inesprg 1   ; 1x 16KB bank of PRG code
	.ineschr 1   ; 1x 8KB bank of CHR data
	.inesmap 0   ; mapper 0 = NROM, no bank swapping
	.inesmir 1   ; background mirroring (ignore for now)
	
;;;;;;; Vars
	.rsset $0000
engine_input      .rs 1 ; 01
engine_prev_input .rs 1 ; 02
temp_volatile     .rs 1 ; 03

	
;;;;;;; Const
BUTTON_A      = %10000000
BUTTON_B      = %01000000
BUTTON_START  = %00100000
BUTTON_SELECT = %00010000
BUTTON_UP     = %00001000
BUTTON_DOWN   = %00000100
BUTTON_LEFT   = %00000010
BUTTON_RIGHT  = %00000001
	
;;;;;;;
	.bank 0
	.org $C000

	.include "Memory.6502"
	.include "Macros.6502"
	.include "PPU.6502"
	.include "Game.6502"
	
engine_ReadInput:
	LDA engine_input
	STA engine_prev_input

	LDA #$01
	STA CONTROL_1_ACCESS_REG
	LDA #$00
	STA CONTROL_1_ACCESS_REG       ; tell both the controllers to latch buttons
	
	LDX #$08
	READ_INPUT_LOOP:
		LDA CONTROL_1_ACCESS_REG
		LSR A
		ROL engine_input

		DEX
		BNE READ_INPUT_LOOP
	RTS


;;;;;;; Program Execution	
engine_Reset:
	SEI          ; disable IRQs
	CLD          ; disable decimal mode
	LDX #$40
	STX CONTROL_2_ACCESS_REG    ; disable APU frame IRQ
	LDX #$FF
	TXS          ; Set up stack
	INX          ; now X = 0
	STX PPU_CONTROL_REG_1    ; disable NMI
	STX PPU_CONTROL_REG_2    ; disable rendering
	STX $4010    ; disable DMC IRQs
	
	JSR ppu_VBlankWait

	CLR_MEM:
		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    ;move all sprites off screen
		INX
		BNE CLR_MEM
	
	JSR ppu_VBlankWait
	
	JSR game_Init
	JSR ppu_Init
	
	GAME_LOOP:
		JSR engine_ReadInput
		JSR game_Tick
		JMP GAME_LOOP
	
; Interupts
	.org $FFFA     ;first of the three vectors starts here
	.dw NMI        ;when an NMI happens (once per frame if enabled) the processor will jump to the label NMI:
	.dw engine_Reset      ;when the processor first turns on or is reset, it will jump to the label RESET:
	.dw 0          ;external interrupt IRQ is not used in this tutorial
	
; Data
	.bank 2
	.org $0000
	.incbin "NESGO.chr"   ;includes 8KB graphics