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63 lines
1.1 KiB
ArmAsm
63 lines
1.1 KiB
ArmAsm
;
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; Ullrich von Bassewitz, 23.09.1998
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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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.import sys_bank, restore_bank
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.importzp cia2, tmp1
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.include "cbm510.inc"
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; ------------------------------------------------------------------------
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; unsigned __fastcall__ readjoy (unsigned char joy);
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.proc _readjoy
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jsr sys_bank ; Switch to the system bank
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tax ; Save joystick number
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; Get the direction bits
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ldy #CIA_PRB
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lda (cia2),y ; Read joystick inputs
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sta tmp1
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; Get the fire bits
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ldy #CIA_PRA
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lda (cia2),y
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; Make the result value
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cpx #$00 ; Joystick 0?
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bne @L1 ; Jump if no
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; Joystick 1, fire is in bit 6, direction in bit 0-3
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asl a
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jmp @L2
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; Joystick 2, fire is in bit 7, direction in bit 5-7
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@L1: ldy #$00 ; High byte of return value
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lsr tmp1
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lsr tmp1
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lsr tmp1
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lsr tmp1
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; Mask the relavant bits, get the fire bit
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@L2: asl a ; Fire bit into carry
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lda tmp1
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and #$0F
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bcc @L3
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ora #$10
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@L3: eor #$1F ; All bits are inverted
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jmp restore_bank
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.endproc
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