support 4 players?

[RodrigoDornelles]

[RodrigoDornelles]

https://wiki.nesdev.org/w/index.php?title=Four_Score
https://forums.nesdev.org/viewtopic.php?p=238969#p238969

;NES 4-player controller reading - written for the ca65 assembler
;- works with FourScore on NES (and AV Famicom afaik)
;- works with Hori adapter on Famicom (up to 4 players)
;- works with expansion port controllers on Famicom (3 players)
;- should work with dual expansion port controllers on Famicom (4 players)
;- has checks in place to allow worn out standard controllers to be replaced by
;  expansion controllers on Famicom (depending on state of playerActive array);
;  This is good behavior for Famicom, a lot of commercially released Famicom
;  games do the same!

;joypad button constants
JOY_RIGHT 	= $01
JOY_LEFT	= $02
JOY_DOWN 	= $04
JOY_UP	 	= $08
JOY_START	= $10
JOY_SELECT	= $20
JOY_B		= $40
JOY_A		= $80

.zeropage
;you'll need to initialize this when the user selects the number of players.
;zero for active players, non-zero for inactive players
playerActive: .res 4

;will hold state of joypads after call to updateInput (use bitwise ops with
;button constants above)
joy1: .res 1
joy2: .res 1
joy3: .res 1
joy4: .res 1

buf4016_0: .res 3
buf4016_1: .res 3
buf4017_0: .res 3
buf4017_1: .res 3
.code

;call this at the beginning of a frame
.proc updateInput ;a,x,y
	
	;not 100% sure anymore why I wrote these out
	;most likely had to do with some zeropage reuse/optimization thing in Micro Mages
	byte2_4016_0 = buf4016_0 + 0
	byte1_4016_0 = buf4016_0 + 1
	byte0_4016_0 = buf4016_0 + 2
	byte2_4017_0 = buf4017_0 + 0
	byte1_4017_0 = buf4017_0 + 1
	byte0_4017_0 = buf4017_0 + 2
	
	byte2_4016_1 = buf4016_1 + 0
	byte1_4016_1 = buf4016_1 + 1
	byte0_4016_1 = buf4016_1 + 2
	byte2_4017_1 = buf4017_1 + 0
	byte1_4017_1 = buf4017_1 + 1
	byte0_4017_1 = buf4017_1 + 2
	
	;reset strobe bit
	ldy #$01
	sty $4016
	dey
	sty $4016
	
	;read joypad and famicom expansion pads as well as multitap adapters
	ldx #3-1
	@byteLoop:
		ldy #8
		@readLoop:
			lda $4016
			lsr a      ; bit0 -> Carry
			rol buf4016_0,x
			lsr a      ; bit1 -> Carry
			rol buf4016_1,x
			lda $4017
			lsr a      ; bit0 -> Carry
			rol buf4017_0,x
			lsr a      ; bit1 -> Carry
			rol buf4017_1,x
			dey
			bne @readLoop
		dex
		bpl @byteLoop
		
	lda byte0_4016_1
	sta joy3
	lda byte0_4017_1
	sta joy4
	
	;on Famicom, it is expected that the expansion port controller
	;can be used to replace a worn-out standard controller #1
	;Let's do that unless a third player joins the party
	lda byte0_4016_0
	ldy playerActive+2 ;player 3
	beq :+
		ora joy3
	:
	sta joy1
	
	;also allow second expansion controller to replace standard controller #2
	lda byte0_4017_0
	ldy playerActive+3 ;player 4
	beq :+
		ora joy4
	:
	sta joy2
	
	@detectMultitap:
		;check 3rd bytes from bit0 reads
		lda byte2_4016_0
		cmp #%00010000 ;$10
		bne @skipFourScore
			lda byte2_4017_0 ;$20
			cmp #%00100000
			bne @skipFourScore
				;FourScore detected
				;2nd bytes hold controller #3/#4 data
				lda byte1_4016_0
				ora joy3
				sta joy3
				lda byte1_4017_0
				ora joy4
				sta joy4
				jmp @skipDetectMultitap
		@skipFourScore:
		
		;check 3rd bytes from bit1 reads
		lda byte2_4016_1
		cmp #%00100000 ;$20
		bne @skipHori
			lda byte2_4017_1
			cmp #%00010000 ;$10
			bne @skipHori
				;hori adapter detected
				;2nd bytes hold controller #3/#4 data
				;allow to replace worn out standard famicom controllers with these as well (4p mode)
				lda byte1_4016_1
				ora joy1
				sta joy1
				lda byte1_4017_1
				ora joy2
				sta joy2
		@skipHori:
		
	@skipDetectMultitap:
	
	rts
.endproc

[RodrigoDornelles]

https://www.devdungeon.com/content/how-mix-c-and-assembly