pulse.cpp

#include "Arduino.h"

/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
 * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
 * to 3 minutes in length, but must be called at least a few dozen microseconds
 * before the start of the pulse.
 *
 * ATTENTION:
 * This function performs better with short pulses in noInterrupt() context
 */

static uint32_t __attribute__((optimize("-O3"))) countPulse(volatile uint32_t *port, uint16_t bit, uint16_t stateMask, unsigned long maxloops) {
	unsigned long width = 0;
	// wait for any previous pulse to end
	while ((*port & bit) == stateMask) {
		if (--maxloops == 0)
			return 0;
	}

	// wait for the pulse to start
	while ((*port & bit) != stateMask) {
		if (--maxloops == 0)
			return 0;
	}

	// wait for the pulse to stop
	while ((*port & bit) == stateMask) {
		if (++width == maxloops)
			return 0;
	}
	return width;
}

uint32_t pulseIn(pin_size_t pin, uint8_t state, uint32_t timeout)
{
	// cache the port and bit of the pin in order to speed up the
	// pulse width measuring loop and achieve finer resolution.  calling
	// digitalRead() instead yields much coarser resolution.
	uint16_t port = digitalPinToPort(pin);
	uint16_t bit = digitalPinToBitMask(pin);
	uint16_t stateMask = state ? bit : 0;

	// convert the timeout from microseconds to a number of times through
	// the initial loop; it takes (roughly) 18 clock cycles per iteration.
	uint32_t maxloops = microsecondsToClockCycles(timeout) / 18;

	uint32_t width = countPulse((volatile uint32_t*)portInputRegister(port), bit, stateMask, maxloops);

	// convert the reading to microseconds. The loop has been determined
	// to be 18 clock cycles long and have about 16 clocks between the edge
	// and the start of the loop. There will be some error introduced by
	// the interrupt handlers.
	if (width)
		return clockCyclesToMicroseconds(width * 18 + 40);
	else
		return 0;
}

/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
 * or LOW, the type of pulse to measure.  Works on pulses from 2-3 microseconds
 * to 3 minutes in length, but must be called at least a few dozen microseconds
 * before the start of the pulse.
 *
 * ATTENTION:
 * this function relies on micros() so cannot be used in noInterrupt() context
 */
uint32_t pulseInLong(uint8_t pin, uint8_t state, unsigned long timeout)
{
	// cache the port and bit of the pin in order to speed up the
	// pulse width measuring loop and achieve finer resolution.  calling
	// digitalRead() instead yields much coarser resolution.
    uint16_t port = digitalPinToPort(pin);
	uint16_t bit = digitalPinToBitMask(pin);
	uint16_t stateMask = state ? bit : 0;

	unsigned long startMicros = micros();

	// wait for any previous pulse to end
	while (((*portInputRegister(port)) & bit) == stateMask) {
		if (micros() - startMicros > timeout)
			return 0;
	}

	// wait for the pulse to start
	while (((*portInputRegister(port)) & bit) != stateMask) {
		if (micros() - startMicros > timeout)
			return 0;
	}

	unsigned long start = micros();
	// wait for the pulse to stop
	while (((*portInputRegister(port)) & bit) == stateMask) {
		if (micros() - startMicros > timeout)
			return 0;
	}
	return micros() - start;
}