/*
  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 <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 = 1 << p.ulPin;
  uint32_t stateMask = state ? bit : 0;

#if defined(__SAMD51__)
  /*
   * The SAMD51 is fast enough to use really obvious code (similar to
   * what was used to produce pulse_asm.S, but using micros() for timing.
   * No assembly required, no conversion of loop counts to times (which is
   * worrisome in the presence of cache.)
   */
  const volatile uint32_t *port = &(PORT->Group[p.ulPort].IN.reg);
  uint32_t usCallStart;  // microseconds at start of call, for timeout.
  uint32_t usPulseStart; // microseconds at start of measured pulse.
  usCallStart = usPulseStart = micros();
  // wait for any previous pulse to end
  while ((*port & bit) == stateMask) {
      if (micros() - usCallStart > timeout)
          return -1;
  }
  // wait for the pulse to start
  while ((*port & bit) != stateMask) {
      usPulseStart = micros();
      if (usPulseStart - usCallStart > timeout)
          return -2;
  }

  // wait for the pulse to stop
  while ((*port & bit) == stateMask) {
      if (micros() - usCallStart > timeout)
          return -3;
  }
  return micros() - usPulseStart;
#else
  // 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(&(PORT->Group[p.ulPort].IN.reg), 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;
#endif // SAMD51
}