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43 lines
1.3 KiB
ArmAsm
43 lines
1.3 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 23.09.1998
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; Adapted for Vic20 by Steve Schmidtke 05.08.2002
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;
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; unsigned readjoy (unsigned char joy);
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;
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.export _readjoy
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.include "vic20.inc"
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; The current implemenation will ignore the joystick number because we do only
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; have one joystick
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.proc _readjoy
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lda #$7F ; mask for VIA2 JOYBIT: sw3
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ldx #$C3 ; mask for VIA1 JOYBITS: sw0,sw1,sw2,sw4
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sei ; necessary?
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ldy VIA2_DDRB ; remember the date of DDRB
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sta VIA2_DDRB ; set JOYBITS on this VIA for input
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lda VIA2_JOY ; read JOYBIT: sw3
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sty VIA2_DDRB ; restore the state of DDRB
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asl ; Shift sw3 into carry
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ldy VIA1_DDRA ; remember the state of DDRA
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stx VIA1_DDRA ; set JOYBITS on this VIA for input
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lda VIA1_JOY ; read JOYBITS: sw0,sw1,sw2,sw4
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sty VIA1_DDRA ; restore the state of DDRA
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cli ; necessary?
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ror ; Shift sw3 into bit 7
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and #$9E ; Mask relevant bits
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eor #$9E ; Active states are inverted
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rts
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.endproc
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