1
0
mirror of https://github.com/cc65/cc65.git synced 2024-12-24 11:31:31 +00:00
cc65/libsrc/cbm510/readjoy.s

63 lines
1.1 KiB
ArmAsm
Raw Normal View History

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