/*
	sonar.c
	Polaroid 6500 routines for Handy Board / Interactive C 
	by Fred Martin, fredm@media.mit.edu
	Sat Nov 22 13:57:35 1997

 	echo signal is connected to tic3/pa0;
 	init signal is pd5 (SS);
 	binh signal is pd4 (SCK)
*/

void sonar_init() {
	bit_set(0x1009, 0x30);		/* ddrd */
	bit_set(0x1021, 1);			/* at tctl2, */
	bit_clear(0x1021, 2);		/* set tic3 for rising edge */
}


int sonar_sample() {
	int start_time;

	poke(0x1023, 1);				/* clear tic3 flag */

	start_time= peekword(0x100e);	/* capture start time */
	bit_set(0x1008, 0x20);			/* trigger pulse */

	while (!(peek(0x1000) & 0x1)) {	/* wait until receive echo */
		if ((peekword(0x100e) - start_time) < 0) {
			/* if too much time has elapsed, abort */
			bit_clear(0x1008, 0x20);
			return -1;
		}
		defer();					/* let others run while waiting */
	}

	bit_clear(0x1008, 0x20);		/* clear pulse trigger */
	
	return peekword(0x1014) - start_time;	/* tic3 has time of echo */
}

int sonar_closeup() {
	int start_time;

	poke(0x1023, 1);				/* clear tic3 flag */
	start_time= peekword(0x100e);
	poke(0x1008, 0x20);
	
	while ((peekword(0x100e) - start_time) < 1000);
	
	bit_set(0x1008, 0x30);			/* turn on BINH */

	while (!(peek(0x1000) & 0x01)) {
		if ((peekword(0x100e) - start_time) < 0) {
			/* if too much time has elapsed, abort */
			bit_clear(0x1008, 0x30);
			return -1;
		}
		defer();
	}

	bit_clear(0x1008, 0x30);

	return peekword(0x1014) - start_time;	/* 0x1014 is tic3 */
}

void sonar_display()
{
	sonar_init();
	
	while (1) {
		int result;
		result= sonar_closeup();
		if (result != -1) printf("%d\n", result);
		else printf("*******\n");
		msleep(50L);
	}
}