;Joystick Constants and Functions for Commander X16 Computer

        SUBR  _JOYSTK

JYSTKS  EQU 2       ;Number of Joysticks

.GETJOY  EQU $FF06   ;Kernal GETJOY Routine
.JYDATA  EQU $02BC   ;Joystick 0 Data
;JOY1  JOY2  
;$02BC $02BF      | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
;            NES  | A | B |SEL|STA|UP |DN |LT |RT |
;            SNES | B | Y |SEL|STA|UP |DN |LT |RT |
;            
;$02BD $20C0      | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
;            NES  | 0 | 0 | 0 | 0 | 0 | 0 | 0 |KBD|
;            SNES | A | X | L | R | 1 | 1 | 1 | 1 |
;            
;$02BE $02C1  $00 = joystick present
;             $FF = joystick not present

;The Joystick Button is mapped to
;A,B on the NES Controller and
;A,B,X,Y on the SNES Controller

;Select and Start are Ignored as Bits 4 and 5 of the return value
;are always 0 because returning $FF means no controller found

;Joystick Bit Masks
JOYUP   EQU $08     ;Up    
JOYDN   EQU $04     ;Down  
JOYLF   EQU $02     ;Left  
JOYRT   EQU $01     ;Right 
JOYB0   EQU $C0     ;Button

;Extended Bit Masks
JOYBA   EQU $80     ;A Button
JOYBB   EQU $40     ;B Button
JOYSL   EQU $20     ;Select
JOYST   EQU $10     ;Start
JOYBL   EQU $08     ;Left Button
JOYBR   EQU $04     ;Right Button
JOYBX   EQU $02     ;X Button
JOYBY   EQU $01     ;Y Button

;Controller Types
JOYKBD  EQU $00     ;Keyboard (NES Emulation)
JOYNES  EQU $01     ;NES Controller
JOYSNS  EQU $02     ;SNS Controller

;joytsk(j) - Read Joystick
;Args: A = Joystick Number (0 or 1)
;Sets: TEMP0 = Inverted Controller Status
;      TEMP1 = Inverted Extended Status
;      TEMP2 - Extended Result (Buttons)
;Destroys: TEMP3
;Returns: A = Joystick Status (Joystick Bit Masks
;         Y = Extended Status (Extended Bit Masks)
;         X = Controller Type (0=Keyboard, 1=NES, 2=SNES)
JOYSTK: CMP #JYSTKS       ;If Invalid Joystick Number
        BCS .JOYSTE       ;  Return ERROR
        STA TEMP0         ;Save Joystick Number
        BYTE $FF
JOYSTL: WAI               ;Wait for Interrupt
        LDA $9F27         ;  Check Vera Interrupt Register
        AND #$01          ;  If Not Vera Interrupt
        BEQ JOYSTL        ;  Loop
        JSR .GETJOY       ;Call Kernal GETJOY Routine
        LDA TEMP0         ;Retrieve Joystick Number
        ASL               ;Multiply it by 3
        ADC TEMP0         ;(Assumes Number<128)
        TAX               ;and Copy to X-Register
        LDA .JYDATA+2,X   ;If Controller Not Present
        BNE .JOYSTE       ;  Return ERROR
        LDA .JYDATA,X     ;Get Base Status
        EOR #$FF          ;Invert Bits
        JSR .JOYEXT       ;Build Extended Results
        AND #$CF          ;Mask off Select and Start
.JOYSTX RTS 

;Return Error
.JOYSTE LDA #$FF
        RTS
        
;Build Extended Result
.JOYEXT STA TEMP0         ;Save Controller Status
        STZ TEMP3         ;Clear Button Mask
        LDA .JYDATA+1,X   ;Get Extended Status
        BIT #$0E          ;Check Bits 1 - 3
        BNE .JOYEXS       ;If NES/Keyboard        
        STA TEMP1         ;    Save for Debugging
        EOR #$01          ;    Invert Extended Bits
        TAX               ;    and Copy to X
        LDA TEMP0         ;  Get Controller Status
        AND #$F0          ;    Isolate Bits 4-7
        TAY               ;    and Copy Back to Y
        BRA .JOYEXX       ;Else
.JOYEXS JSR .JOYSNS       ;  Process SNES Buttons 
.JOYEXX LDA TEMP0         ;Restore Controller Status
        ORA TEMP3         ;Combine Buttons
        RTS

;Process SNES Buttons
.JOYSNS LDX #2            ;Set Controller Type to 2
        EOR #$FF          ;Invert Extended Bits
        STA TEMP1         ;  and Save Result
        AND #$C0          ;Isolate SNES A,X Buttons
        STA TEMP3         ;and Save in Button Mask
        LDA TEMP1         ;Retrieve Extended Buttons
        AND #$30          ;Isolate L and R
        ASL               ;and Shift to Bits 2 and 3
        ASL               
        BIT TEMP1         ;Get Ext Status High Bits
        BCC +2            ;If Extended Bit 7 was Set
        ORA #$80          ;  Set Buttons Bit 7 (A)
        BVC +2            ;If Extended Bit 6 was Set
        ORA #$20          ;  Set Buttons Bit 1 (X)
        STA TEMP2         ;Save Buttons A,X,L,R
        LDA TEMP0         ;Retrieve Controller Status
        AND #$30          ;Isolate Select and Start
        ORA TEMP2         ;Combine with A,X,L,R
        BIT TEMP2         ;Get Status High Bits
        BCC +2            ;If Status Bit 7 was Set
        ORA #$40          ;  Set Buttons Bit 6 (B)
        BVC +2            ;If Status Bit 6 was Set
        ORA #$01          ;  Set Buttons Nit 0 (Y)
        STA TEMP2         ;Save Buttons in TEMP2
        TAY               ;  and Copy to Y
        RTS