cc65/libsrc/lynx/cgetc.s

;
; Karri Kaksonen, Harry Dodgson 2006-01-07
;
; char cgetc (void);
;

       	.export		_cgetc
       	.import		_kbhit
	.import		KBEDG
	.import		KBSTL

; --------------------------------------------------------------------------
; The Atari Lynx has a very small keyboard - only 3 keys
; Opt1, Opt2 and Pause.
; But the designers have decided that pressing Pause and Opt1 at the
; same time means Restart and pressing Pause and Opt2 means Flip screen.

; For "easter egg" use I have also included all three keys pressed '?'
; and Opt1 + Opt2 pressed '3'.
; So the keyboard returns '1', '2', '3', 'P', 'R', 'F' or '?'.

_cgetc:
	lda	KBSTL
	ora	KBEDG
	bne	@L1
    	jsr	_kbhit	       	; Check for char available
        tax				; Test result
	bra	_cgetc
@L1:
       	ldx	#0
	and	#1
	beq	@L6
	lda	KBEDG		; Pause button is pressed
	and	#$0c
	beq	@L3
	ora	KBSTL
@L2:
	bit	#$04
	beq	@L4			; Pause + Opt 1 = Reset
	bit	#$08
	beq	@L5			; Pause + Opt 2 = Flip
	lda	#'?'			; All buttons pressed
       	rts
@L3:
	lda	KBSTL		; Pause alone was the last placed button
	and	#$0c
	bne	@L2
	lda	#'P'			; Pause pressed
       	rts
@L4:
	lda	#'R'			; Reset pressed
       	rts
@L5:
	lda	#'F'			; Flip pressed
       	rts
@L6:
	lda	KBEDG		; No Pause pressed
	ora	KBSTL
	bit	#$08
	beq	@L8
	bit	#$04
	beq	@L7
	lda	#'3'			; opt 1 + opt 2 pressed
	rts
@L7:
	lda	#'1'			; opt 1 pressed
	rts
@L8:
	lda	#'2'			; opt 2 pressed
	rts