inkey68k.lib

open source of basic interpreter of 68

*
*  inkey68k.lib      read a character from the input device
*
*  This function tests the input device for the presence of a character.
*  If a character is available, this routine returns the character in
*  the low byte of d0, sets bit 8, and clears all higher bytes.  If no
*  character is available, this routine returns 0 in d0.
*
*  This is the low-level SBasic68k input routine.  You can change this
*  routine, if you wish, to support other input devices.  Make sure,
*  however, that you retain _inkey as the subroutine's name.
*
*  This routine preserves all registers.
*

*
*  This works with 332bug on Motorola's 68332 development
*  board.  Since character I/O is target platform specific,
*  you need to develop your own _inkey function.
*

_inkey
	movem.l	d1-d7/a0-a6,-(a7)	save regs

	trap	#15			332bug system call
	dc.w	$1			test serial port
	beq	_ink1			branch if no char

	subq.l	#2,a7			reserve stack space
	trap	#15			332bug system call
	dc.w	$0			get char to stack
	clr.l	d0			ready the 32-bit variable
	move.w	(a7)+,d0		fetch char to d0
	lsr.w	#8,d0			key is in second byte
	bset.l	#8,d0			force bit 8 on to flag char
	bra	_inkx			all done
_ink1
	clr.l	d0			show no char
_inkx
	movem.l	(a7)+,d1-d7/a0-a6	restore regs
	rts