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74 lines
1.5 KiB
ArmAsm
74 lines
1.5 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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.proc _readjoy
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tax ; Joystick number into X
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bne joy2
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; Read joystick 1
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joy1: lda #$7F
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ldx #$C3
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sei ; necessary?
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ldy VIA1_DDRA
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stx VIA1_DDRA
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ldx VIA1_JOY
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sty VIA1_DDRA
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ldy VIA2_DDRB
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sta VIA2_DDRB
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lda VIA2_JOY ; sw3 happens to be the 7th bit (i.e negative)
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sty VIA2_DDRB
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cli ; necessary?
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; all this mess below tries to normalize the returned results (see joystick.h)
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; by shifting bits around and inserting switch3 (right).
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; easier (and far smaller) would have been just to return the bits where they
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; lay and just #ifdef different joystick constants for the Vic20.
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bmi s3_off ; must stay valid from the VIA2_JOY load
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txa ; state: sw3 on, fire ?
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and #$20 ; find out if fire has been pressed
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bne f_off1
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txa ; state: sw3 on, fire on
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lsr
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lsr
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and #$07
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eor #$1F
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rts
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f_off1: txa ; state: sw3 on, fire off
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lsr
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lsr
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and #$07
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eor #$0F
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rts
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s3_off: txa ; state: sw3 off, fire ?
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and #$20 ; find out if fire has been pressed
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bne f_off2 ; yeah, that's just about my sentiment by now
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txa ; state: sw3 off, fire on
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lsr
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lsr
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and #$07
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eor #$17
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rts
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f_off2: txa ; state: sw3 off, fire off
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lsr
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lsr
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and #$07
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eor #$07
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rts
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; Read joystick 2 + (just return joy1)
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joy2: jmp joy1 ; stub for more joysticks (pointless?)
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.endproc
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