;4 player adapter sample code by gpz/hit
;D&H adapter ASM
;---------------------------------------

joy3reg  = $02  ; example joy-regs
joy4reg  = $03

btemp    = $04  ; temp for display

;---------------------------------------
; main
;---------------------------------------

         *= $1000

         ;
         ; usual irq setup
         ;

         sei
         lda #>irq
         sta $0315
         lda #<irq
         sta $0314
         lda #$1b
         sta $d011
         lda #$7f
         sta $dc0d
         lda #$ff
         sta $d012
         lda #$01
         sta $d01a

         ;
         ; print info
         ;

         ldx #$00
loop     .var *
         lda screen,x
         jsr $ffd2
         inx
         cpx #22
         bne loop

         jsr setup    ; cia setup for adapter

         cli

         jmp *

;---------------------------------------
; interupt calls other routines
;---------------------------------------
irq

         inc $d020

         jsr read   ; read adapter (takes about 2 rasterlines)

         inc $d020

         ldx #(40*1)+4
         lda $dc00
         jsr displaybits

         ldx #(40*2)+4
         lda $dc01
         jsr displaybits

         ldx #(40*3)+4
         lda joy3reg
         jsr displaybits

         ldx #(40*4)+4
         lda joy4reg
         jsr displaybits

         lda #$00
         sta $d020

         inc $d019
         jmp $febc

;---------------------------------------
; displays 5 lowest bits of joystick-reg
;---------------------------------------
displaybits

         rol a
         rol a
         rol a

         sta btemp

         ldy #$00
loop     .var *

         rol btemp
         bcc skip1

         lda #"-"
         sta $0400,x
         jmp skip2
skip1
         lda #"*"
         sta $0400,x
skip2
         inx
         iny
         cpy #$05
         bne loop

         rts

;---------------------------------------
screen
         .text "{clr/home}joy brldu"
         .text " 1{return}"
         .text " 2{return}"
         .text " 3{return}"
         .text " 4{return}"

;---------------------------------------

;---------------------------------------
read
;---------------------------------------
; reads adapter and composes the
; additional virtual joystick-registers
;---------------------------------------
;this code demonstrates how to read the
;additional 2 joysticks and how to com-
;pose 2 'virtual' joystick-registers
;that can be processed exactly like the
;usual ($dc00/$dc01) ones.
;---------------------------------------
         ;
         ; save cia 2 registers
         ;

         lda $dd00
         sta ciasave1+1
         lda $dd02
         sta ciasave2+1

         ;
         ; read directions joy 3+joy 4
         ;

         lda $dd01 ;read cia 2 port b
         sta temp+1

         and #$0f
         sta joy3reg

temp     lda #$00
         lsr a
         lsr a
         lsr a
         lsr a
         sta joy4reg

         ;
         ; read button joy 3
         ;

         lda $dd02      ;cia 2 port a
         and #%11111011 ;data direction
         sta $dd02      ;=> bit 2 input

         lda $dd00      ;read cia 2 p.A
         and #%00000100 ;check bit 2
         asl a
         asl a
         ora joy3reg
         sta joy3reg

         ;
         ; read button joy 4
         ;

         lda #$ff ;serial data register
         sta $dc0c;=> writing $ff causes
                  ;cia to output some
                  ;count signals at cnt1

         lda $dd0c ;read cia 2 serial in
         beq fire  ;button press if zero

         lda joy4reg
         ora #%00010000
         sta joy4reg

fire

         ;
         ; restore cia 2 registers
         ;

ciasave1 lda #$00
         sta $dd00
ciasave2 lda #$00
         sta $dd02

         rts

;---------------------------------------
setup
;---------------------------------------
;warning: do not mess around with this
;         unless you really know what
;         you are doing! wrong cia setup
;         may toast your cia's !
;---------------------------------------

         ;
         ; cia 2 setup
         ;

         lda #$00  ; port b direction
         sta $dd03 ; => input

         lda #$01
         sta $dd04 ; timer a lowbyte
         lda #$00
         sta $dd05 ; timer a highbyte

         lda #%00010001
         sta $dd0e ; control register a
                   ; timer: start
                   ;        continous
                   ;        forced load
                   ; serial port: input

         ;
         ; cia 1 setup
         ;

         lda #$01
         sta $dc04 ; timer a lowbyte
         lda #$00
         sta $dc05 ; timer a highbyte

         lda #%01010001
         sta $dc0e ; control register a
                   ; timer: start
                   ;        continous
                   ;        forced load
                   ; serial port: output

         lda #$ff ;serial data register
         sta $dc0c;=> writing $ff causes
                  ;cia to output some
                  ;count signals at cnt1
         rts