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/*
Copyright (c) 2015 Arduino LLC. All right reserved.
This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
See the GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "nrf.h"
#include <Arduino.h>
// See pulse_asm.S
extern unsigned long countPulseASM(const volatile uint32_t *port, uint32_t bit, uint32_t stateMask, unsigned long maxloops);
/* 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. */
uint32_t pulseIn(uint32_t pin, uint32_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.
// PinDescription p = g_APinDescription[pin];
uint32_t bit = digitalPinToBitMask(pin); //p.ulPin;
uint32_t stateMask = state ? bit : 0;
// convert the timeout from microseconds to a number of times through
// the initial loop; it takes (roughly) 13 clock cycles per iteration.
uint32_t maxloops = microsecondsToClockCycles(timeout) / 13;
uint32_t width = countPulseASM(portInputRegister(digitalPinToPort(pin)), bit, stateMask, maxloops);
// convert the reading to microseconds. The loop has been determined
// to be 13 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 * 13 + 16);
else
return 0;
}
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