comparison: sanguino/cores/arduino/wiring_pulse.c
sanguino/cores/arduino/wiring_pulse.c
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| 1:b584642d4f58 | 2:b373b0288715 |
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| 1 /* | |
| 2 wiring_pulse.c - pulseIn() function | |
| 3 Part of Arduino - http://www.arduino.cc/ | |
| 4 | |
| 5 Copyright (c) 2005-2006 David A. Mellis | |
| 6 | |
| 7 This library is free software; you can redistribute it and/or | |
| 8 modify it under the terms of the GNU Lesser General Public | |
| 9 License as published by the Free Software Foundation; either | |
| 10 version 2.1 of the License, or (at your option) any later version. | |
| 11 | |
| 12 This library is distributed in the hope that it will be useful, | |
| 13 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 15 Lesser General Public License for more details. | |
| 16 | |
| 17 You should have received a copy of the GNU Lesser General | |
| 18 Public License along with this library; if not, write to the | |
| 19 Free Software Foundation, Inc., 59 Temple Place, Suite 330, | |
| 20 Boston, MA 02111-1307 USA | |
| 21 | |
| 22 $Id: wiring.c 248 2007-02-03 15:36:30Z mellis $ | |
| 23 */ | |
| 24 | |
| 25 #include "wiring_private.h" | |
| 26 #include "pins_arduino.h" | |
| 27 | |
| 28 /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH | |
| 29 * or LOW, the type of pulse to measure. Works on pulses from 2-3 microseconds | |
| 30 * to 3 minutes in length, but must be called at least a few dozen microseconds | |
| 31 * before the start of the pulse. */ | |
| 32 unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout) | |
| 33 { | |
| 34 // cache the port and bit of the pin in order to speed up the | |
| 35 // pulse width measuring loop and achieve finer resolution. calling | |
| 36 // digitalRead() instead yields much coarser resolution. | |
| 37 uint8_t bit = digitalPinToBitMask(pin); | |
| 38 uint8_t port = digitalPinToPort(pin); | |
| 39 uint8_t stateMask = (state ? bit : 0); | |
| 40 unsigned long width = 0; // keep initialization out of time critical area | |
| 41 | |
| 42 // convert the timeout from microseconds to a number of times through | |
| 43 // the initial loop; it takes 16 clock cycles per iteration. | |
| 44 unsigned long numloops = 0; | |
| 45 unsigned long maxloops = microsecondsToClockCycles(timeout) / 16; | |
| 46 | |
| 47 // wait for any previous pulse to end | |
| 48 while ((*portInputRegister(port) & bit) == stateMask) | |
| 49 if (numloops++ == maxloops) | |
| 50 return 0; | |
| 51 | |
| 52 // wait for the pulse to start | |
| 53 while ((*portInputRegister(port) & bit) != stateMask) | |
| 54 if (numloops++ == maxloops) | |
| 55 return 0; | |
| 56 | |
| 57 // wait for the pulse to stop | |
| 58 while ((*portInputRegister(port) & bit) == stateMask) { | |
| 59 if (numloops++ == maxloops) | |
| 60 return 0; | |
| 61 width++; | |
| 62 } | |
| 63 | |
| 64 // convert the reading to microseconds. The loop has been determined | |
| 65 // to be 20 clock cycles long and have about 16 clocks between the edge | |
| 66 // and the start of the loop. There will be some error introduced by | |
| 67 // the interrupt handlers. | |
| 68 return clockCyclesToMicroseconds(width * 21 + 16); | |
| 69 } |
