;SNES Mouse read routine
;(C) 1999, 2000 Realtime Simulations and Roleplaying games
;By Grog

;ReadSNESMouse -- Use Ports $4016 and $4017 to read the SNES mouse (port 2)
;In: none
;Out: X=delta X
;     Y=delta Y
ReadSNESMouse:
        LDA #$01
        STA $4016       ;Reset old-style port read

        LDA #$00
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        BPL +
        AND #$7F        ;Remove 1s complement sign
        EOR #$FF        ;Invert
        INC A           ;Add one (2s complement)
+       TAY

        LDA #$00
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        JSR ReadPort4017Bit
        ROL A
        BPL +
        AND #$7F        ;Remove 1s complement sign
        EOR #$FF        ;Invert
        INC A           ;Add one (2s complement)
+       TAX

        RTS


ReadPort4017Bit:
        PHA
        LDA $4017
        CLC
        ADC #'0'
        JSL Print
        LSR
        PLA
        RTS