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/*
wiring_pulse.c - pulseIn() function
Part of Arduino - http://www.arduino.cc/
Copyright (c) 2005-2006 David A. Mellis
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., 59 Temple Place, Suite 330,
Boston, MA 02111-1307 USA
$Id: wiring.c 248 2007-02-03 15:36:30Z mellis $
*/
#include "wiring_private.h"
#include "pins_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 10 microseconds
* to 3 minutes in length, but must be called at least N microseconds before
* the start of the pulse. */
unsigned long pulseIn(uint8_t pin, uint8_t state)
{
// 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.
uint8_t bit = digitalPinToBitMask(pin);
uint8_t port = digitalPinToPort(pin);
uint8_t stateMask = (state ? bit : 0);
unsigned long width = 0; // keep initialization out of time critical area
// wait for the pulse to start
while ((*portInputRegister(port) & bit) != stateMask)
;
// wait for the pulse to stop
while ((*portInputRegister(port) & bit) == stateMask)
width++;
// convert the reading to microseconds. The loop has been determined
// to be 10 clock cycles long and have about 12 clocks between the edge
// and the start of the loop. There will be some error introduced by
// the interrupt handlers.
return clockCyclesToMicroseconds(width * 10 + 12);
}
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