WaspmoteAPI: wiring_pulse.c Source File

00001 /*
00002  *  Copyright (c) 2005-2006 David A. Mellis
00003  *
00004  *  This program is free software: you can redistribute it and/or modify
00005  *  it under the terms of the GNU Lesser General Public License as published by
00006  *  the Free Software Foundation, either version 2.1 of the License, or
00007  *  (at your option) any later version.
00008    
00009  *  This program is distributed in the hope that it will be useful,
00010  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
00011  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00012  *  GNU Lesser General Public License for more details.
00013   
00014  *  You should have received a copy of the GNU Lesser General Public License
00015  *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
00016  */
00017  
00018  
00019 #include "wiring_private.h"
00020 #include "pins_waspmote.h"
00021 
00022 /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
00023  * or LOW, the type of pulse to measure.  Works on pulses from 10 microseconds
00024  * to 3 minutes in length, but must be called at least N microseconds before
00025  * the start of the pulse. */
00026 unsigned long pulseIn(uint8_t pin, uint8_t state)
00027 {
00028         // cache the port and bit of the pin in order to speed up the
00029         // pulse width measuring loop and achieve finer resolution.  calling
00030         // digitalRead() instead yields much coarser resolution.
00031         uint8_t bit = digitalPinToBitMask(pin);
00032         uint8_t port = digitalPinToPort(pin);
00033         uint8_t stateMask = (state ? bit : 0);
00034         unsigned long width = 0; // keep initialization out of time critical area
00035         
00036         // wait for the pulse to start
00037         while ((*portInputRegister(port) & bit) != stateMask)
00038                 ;
00039         
00040         // wait for the pulse to stop
00041         while ((*portInputRegister(port) & bit) == stateMask)
00042                 width++;
00043 
00044         // convert the reading to microseconds. The loop has been determined
00045         // to be 10 clock cycles long and have about 12 clocks between the edge
00046         // and the start of the loop. There will be some error introduced by
00047         // the interrupt handlers.
00048         return clockCyclesToMicroseconds(width * 10 + 12); 
00049 }