70 lines
2.6 KiB
C
70 lines
2.6 KiB
C
/*
|
|
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 2-3 microseconds
|
|
* to 3 minutes in length, but must be called at least a few dozen microseconds
|
|
* before the start of the pulse. */
|
|
unsigned long pulseIn(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.
|
|
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
|
|
|
|
// convert the timeout from microseconds to a number of times through
|
|
// the initial loop; it takes 16 clock cycles per iteration.
|
|
unsigned long numloops = 0;
|
|
unsigned long maxloops = microsecondsToClockCycles(timeout) / 16;
|
|
|
|
// wait for any previous pulse to end
|
|
while ((*portInputRegister(port) & bit) == stateMask)
|
|
if (numloops++ == maxloops)
|
|
return 0;
|
|
|
|
// wait for the pulse to start
|
|
while ((*portInputRegister(port) & bit) != stateMask)
|
|
if (numloops++ == maxloops)
|
|
return 0;
|
|
|
|
// wait for the pulse to stop
|
|
while ((*portInputRegister(port) & bit) == stateMask) {
|
|
if (numloops++ == maxloops)
|
|
return 0;
|
|
width++;
|
|
}
|
|
|
|
// convert the reading to microseconds. The loop has been determined
|
|
// to be 20 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.
|
|
return clockCyclesToMicroseconds(width * 21 + 16);
|
|
}
|