| /* |
| 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); |
| } |