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;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