#define until(a) while(!(a))

#define IOADDR 0xff0000
#define SIOBASE (IOADDR + 0x20)

/*
 * rcon bits
 */

#define RENABLE (1 << 1)		/* receiver enable */

/*
 * fifo status bits.
 */

#define FREADY (1 << 6)

/*
 * sstatus bits.
 */

#define OUTREADY (1 << 0)

struct sio
	{
	char
		addr0,		/* low byte dma address */
		addr1,		/* high byte dma address */
		addr2,		/* extended byte of dma address */

		rcon,		/* receiver control port */

		count0,		/* low byte of dma  count */
		count1,		/* high byte of dma count */

		enable,		/* start / stop enable */
		dmacon,		/* dma control and status */

		sdata,		/* uart data port */
		sstatus,	/* uart status port */
		smode,		/* uart mode register */
		scommand,	/* uart command register */

		fstatus,	/* fifo status */
		fdata,		/* fifo data */

		dmaglob,	/* global dma status */
		select;		/* tty select port */
	};

static struct sio *s4;

#define REG1 0x27
#define REG2 0x6e
#define REG3 0x7d		/* 9600 */
#define REG3_1200 0x78		/* 1200 */
#define REG3_300 0x76		/* 300 */

/*
 * initialize the device
 */

sopen (a, b)
	{
	s4 = (struct sio *) SIOBASE;

	s4->select = a;
	
	s4->scommand = REG1;


	s4->smode = REG2;

	if (b == 1200)
		s4->smode = REG3_1200;

	else if (b == 300)
		s4->smode = REG3_300;

	else
		s4->smode = REG3;

	s4->rcon = RENABLE;
	}

/*
 * turn off the device
 */

sclose (a)
	{
	s4->select = a;
	s4->rcon = 0;		/* disable receiver */
	}

/*
 * read a character in
 * low byte
 *
 * Status in high byte.
 */


sread ()
	{
	int a;

	until(s4->fstatus & FREADY)
		;

	a = s4->fstatus << 8;
	return a | s4->fdata;
	}

/* 
 * Write character c to port p
 */

swrite (c, p)
	{
	s4->select = p;

	until(s4->sstatus & OUTREADY)
		;

	s4->sdata = c;
	}