/*
 *	Serial port driver for 16Cxx chips
 *	using RTCC.
 */

/*
 *	Tunable parameters
 */

#include	<pic.h>
#include	<conio.h>

/*	Transmit and Receive port bits */

static bit	TxData @ (unsigned)&PORTA*8+3;		/* bit3 in port A */
static bit	RxData @ (unsigned)&PORTA*8+2;		/* bit2 in port A */

/*	Xtal frequency */

#define	XTAL	4000000

/*	Baud rate	*/

#define	BRATE	9600

/*	Don't change anything else */

#define	DLY		3		/* cycles per loop */
#define	TX_OHEAD	20		/* overhead cycles per loop */
#define	RX_OHEAD	14		/* receiver overhead per loop */

#define	DELAY(ohead)	(((XTAL/4/BRATE)-(ohead))/DLY)

void
putch(char c)
{
	unsigned char	dly, bitno;

	bitno = 11;

	TRISA = 7;
	for(bitno = 11 ;; --bitno) {

		switch(bitno) {

		case 11:		/* start bit */
			TxData = 0;
			break;

		case 10:
		case 9: case 8: case 7: case 6:
		case 5: case 4: case 3:
			if(c & 1)
				TxData = 1;
			if(!(c & 1))
				TxData = 0;
			c >>= 1;
			break;

		case 2:
			TxData = 1;	/* stop bit */
		case 1:
			break;
		case 0:
			return;
		}
		dly = DELAY(TX_OHEAD);
		do
			/* nix */ ;
		while(--dly);
	}
}

char
getch(void)
{
	unsigned char	c, bitno, dly;

	for(;;) {
		while(RxData)
			continue;	/* wait for start bit */
		dly = DELAY(3)/2;
		do
			/* nix */;
		while(--dly);
		if(RxData)
			continue;	/* twas just noise */
		bitno = 8;
		c = 0;
		do {
			c >>= 1;
			dly = DELAY(RX_OHEAD);
			do
				/* nix */;
			while(--dly);
			if(RxData)
				c |= 0x80;
		} while(--bitno);
		return c;
	}
}