dcf77.c

WWVB receiver using AVR.

/* $Id: dcf77.c,v 1.10 2005/11/01 15:47:10 simimeie Exp $
 * Functions for communicating with the DCF module and calculating time
 */ 

#define BV _BV
#include <avr/io.h>
#include <avr/signal.h>
#include "dcf77.h"
#include "timers.h"
#include "ledmodule.h"
#include "timeformat.h"
#ifdef DCFDEBUG
#include "debugconsole.h"
#endif

/* These two defines allow us to easily switch between inverted and
 * not-inverted output. */
#define DCFHI BV(PIND2)
#define DCFLO 0

/* if the last bit was received more than 1.5 seconds ago, then this
 * signals the start of a minute. */
#define BORDER_MINSTART ((3 * TICKSPERSECOND) / 2)
#define BORDERU_1BIT ((24 * TICKSPERSECOND) / 100)
#define BORDERL_1BIT ((16 * TICKSPERSECOND) / 100)
#define BORDERU_0BIT ((14 * TICKSPERSECOND) / 100)
#define BORDERL_0BIT (( 6 * TICKSPERSECOND) / 100)

#define BITDINDEX(x) ((x & 0xF8) >> 3)
#define getbit(x) (bitdata[BITDINDEX(x)] & BV(x & 0x07))
#define getbitval(x) ((getbit(x) == 0) ? 0 : 1)
static uint8_t bitdata[8];
static uint8_t bitsrecvd;
static uint8_t lastval;
struct tickdata lastchange; /* "Timestamp" of last change */
struct dcftime dcftime[2];
uint8_t dcfvalid;

uint8_t sumbits(uint8_t start, uint8_t end) {
	uint8_t mult = 1;
	uint8_t res = 0;
	while (start <= end) {
		res += getbitval(start) * mult;
		if (mult == 8) {
			mult = 10;
		} else {
			mult <<= 1; /*  * 2 */
		}
		start++;
	}
	return res;
}

uint8_t paritybits(uint8_t start, uint8_t end) {
	uint8_t res = 0;
	while (start <= end) {
		if (getbit(start)) {
			res = !res;
		}
		start++;
	}
	return res;
}

SIGNAL(SIG_INTERRUPT0) {
	uint8_t val = PIND;
	struct tickdata curticks;
	uint16_t tickdiff;
	gettickdata(&curticks);
	val &= BV(PIND2);
	if (val == lastval) { /* No change at all? why the IRQ then? */
		return;
	}
	lastval = val;
	tickdiff = (curticks.seconds - lastchange.seconds) * TICKSPERSECOND
	         + (curticks.ticks - lastchange.ticks);
	lastchange = curticks;
	if (val == DCFHI) { /* Signal changed to high */
		if (tickdiff > BORDER_MINSTART) { /* Start of a new minute */
			led_statusleds &= (uint8_t)~led_status_dcfgood;
			if (bitsrecvd == 59) {
				/* Sanity checks */
				if (getbit(0)) {
					/* Bit 0 always has to be 0 */
					bitsrecvd++;
				}
				if (!getbit(20)) {
					/* Bit 20 always has to be 1 */
					bitsrecvd++;
				}
				if (paritybits(21, 28) != 0) {
					bitsrecvd++;
				}
				if (paritybits(29, 35) != 0) {
					bitsrecvd++;
				}
				if (paritybits(36, 58) != 0) {
					bitsrecvd++;
				}
				if (getbit(17) == getbit(18)) {
					bitsrecvd++;
				}
				if (bitsrecvd == 59) {
					struct brokentime bt;
					/* None of the sanity checks failed
					 * - time should be valid. */
					led_statusleds |= led_status_dcfgood;
					/* Decode data now */
					dcfvalid = !dcfvalid;
					bt.year  = sumbits(50, 57);
					bt.month = sumbits(45, 49);
					bt.day   = sumbits(36, 41);
					bt.hour  = sumbits(29, 34);
					bt.min   = sumbits(21, 27);
					bt.sec   = 0;
					dcftime[dcfvalid].timestamp = bttots(&bt);
					dcftime[dcfvalid].ticksecs = curticks.seconds;
					dcftime[dcfvalid].issummertime = getbit(17);
					timers_zero();
					gettickdata(&lastchange);
				}
			}
#ifdef DCFDEBUG
			debugconsole_printtext("\r\n");
#endif
			bitsrecvd = 0;
		}
	} else { /* Signal changed to low */
#ifdef LEDMODULE
		led_statusleds |= led_status_dcfbit;
#endif
		if (bitsrecvd > 60) { return; }
		if ((tickdiff > BORDERL_1BIT)
		 && (tickdiff < BORDERU_1BIT)) { /* valid '1' bit */
			bitdata[BITDINDEX(bitsrecvd)] |= BV(bitsrecvd & 0x07);
			bitsrecvd++;
#ifdef DCFDEBUG
			debugconsole_printtext("1");
#endif
		} else if ((tickdiff > BORDERL_0BIT)
		 && (tickdiff < BORDERU_0BIT)) { /* valid '0' bit */
			bitdata[BITDINDEX(bitsrecvd)] &= (uint8_t)~BV(bitsrecvd & 0x07);
			bitsrecvd++;
#ifdef DCFDEBUG
			debugconsole_printtext("0");
		} else {
			debugconsole_printtext("X");
#endif
		}
	}
}

void dcf77_init(void) {
	/* Set the IRQ line so that we get an IRQ whenever it changes
	 * its logical level (0 -> 1 or 1 -> 0) */
	MCUCR |= BV(ISC00);
	/* And allow IRQs from that port */
	GICR |= BV(INTF0);
	/* Enable PullUp on Port D pin 2. The Port is already a input on
	 * startup. */
	PORTD |= BV(PD2);
}