# HG changeset patch
# User John Tsiombikas <nuclear@member.fsf.org>
# Date 1383334394 -7200
# Node ID 4ea5d2920f89490c9c40905603614b95ae76cb23
# Parent  050c04723d3761233f3db29392e2e2ea910f24d4
made the timing more accurate

diff -r 050c04723d37 -r 4ea5d2920f89 pwcdecode.c
--- a/pwcdecode.c	Fri Nov 01 09:40:20 2013 +0200
+++ b/pwcdecode.c	Fri Nov 01 21:33:14 2013 +0200
@@ -75,20 +75,15 @@
 	printf("initializing...");
 
 	TCCR1B |= (1 << ICES1);	/* set first capture to occur on a rising edge */
-	TCCR1B = (TCCR1B & 0xf8) | 1;	/* no prescaling */
+	TCCR1B = (TCCR1B & 0xf8) | 2;	/* /8 prescaling */
 	TIMSK1 |= (1 << ICIE1);	/* enable timer1 input capture interrupt */
 	sei();
 
 	for(;;) {
-		static int blink = 0;
-
-		PORTB = blink ? 1 : 0;
-		blink = (blink + 1) & 1;
-
 		lcd_set_cursor_addr(0);
 		printf("pulse time: %u us  ", pulse_time);
 		lcd_set_cursor_addr(64);
-		printf("pos: %u%%          ", (pulse_time - 1000) / 10);
+		printf("pos: %u %%          ", (pulse_time - 1000) / 10);
 		_delay_ms(100);
 	}
 	return 0;
@@ -97,18 +92,22 @@
 ISR(TIMER1_CAPT_vect)
 {
 	static int rising;
+	static unsigned int start_time;
 
 	rising = !rising;
 	if(rising) {
-		/* rising edge: reset the timer */
-		TCNT1 = 0;
+		/* start counting ... */
+		start_time = ICR1;
 		/* and set a falling edge trigger */
 		TCCR1B &= ~(1 << ICES1);
 	} else {
 		/* falling edge: calculate the time since the last rise */
-		pulse_time = ICR1;
+		pulse_time = (ICR1 - start_time) * 8;	/* 8x to cancel out prescaling */
 		/* and set a rising edge trigger */
 		TCCR1B |= 1 << ICES1;
+
+		/* also clear the timer so it won't overflow */
+		TCNT1 = 0;
 	}
 }