| 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 |
|
| 23 | #include "wiring_private.h" |
| 24 | #include "pins_arduino.h" |
| 25 |
|
| 26 | /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH |
| 27 | * or LOW, the type of pulse to measure. Works on pulses from 2-3 microseconds |
| 28 | * to 3 minutes in length, but must be called at least a few dozen microseconds |
| 29 | * before the start of the pulse. |
| 30 | * |
| 31 | * This function performs better with short pulses in noInterrupt() context |
| 32 | */ |
| 33 | unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout) |
| 34 | { |
| 35 | // cache the port and bit of the pin in order to speed up the |
| 36 | // pulse width measuring loop and achieve finer resolution. calling |
| 37 | // digitalRead() instead yields much coarser resolution. |
| 38 | uint8_t bit = digitalPinToBitMask(pin); |
| 39 | uint8_t port = digitalPinToPort(pin); |
| 40 | uint8_t stateMask = (state ? bit : 0); |
| 41 |
|
| 42 | // convert the timeout from microseconds to a number of times through |
| 43 | // the initial loop; it takes approximately 16 clock cycles per iteration |
| 44 | unsigned long maxloops = microsecondsToClockCycles(timeout)/16; |
| 45 |
|
| 46 | unsigned long width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops); |
| 47 |
|
| 48 | // prevent clockCyclesToMicroseconds to return bogus values if countPulseASM timed out |
| 49 | if (width) |
| 50 | return clockCyclesToMicroseconds(width * 16 + 16); |
| 51 | else |
| 52 | return 0; |
| 53 | } |
| 54 |
|
| 55 | /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH |
| 56 | * or LOW, the type of pulse to measure. Works on pulses from 2-3 microseconds |
| 57 | * to 3 minutes in length, but must be called at least a few dozen microseconds |
| 58 | * before the start of the pulse. |
| 59 | * |
| 60 | * ATTENTION: |
| 61 | * this function relies on micros() so cannot be used in noInterrupt() context |
| 62 | */ |
| 63 | unsigned long pulseInLong(uint8_t pin, uint8_t state, unsigned long timeout) |
| 64 | { |
| 65 | // cache the port and bit of the pin in order to speed up the |
| 66 | // pulse width measuring loop and achieve finer resolution. calling |
| 67 | // digitalRead() instead yields much coarser resolution. |
| 68 | uint8_t bit = digitalPinToBitMask(pin); |
| 69 | uint8_t port = digitalPinToPort(pin); |
| 70 | uint8_t stateMask = (state ? bit : 0); |
| 71 |
|
| 72 | unsigned long startMicros = micros(); |
| 73 |
|
| 74 | // wait for any previous pulse to end |
| 75 | while ((*portInputRegister(port) & bit) == stateMask) { |
| 76 | if (micros() - startMicros > timeout) |
| 77 | return 0; |
| 78 | } |
| 79 |
|
| 80 | // wait for the pulse to start |
| 81 | while ((*portInputRegister(port) & bit) != stateMask) { |
| 82 | if (micros() - startMicros > timeout) |
| 83 | return 0; |
| 84 | } |
| 85 |
|
| 86 | unsigned long start = micros(); |
| 87 | // wait for the pulse to stop |
| 88 | while ((*portInputRegister(port) & bit) == stateMask) { |
| 89 | if (micros() - startMicros > timeout) |
| 90 | return 0; |
| 91 | } |
| 92 | return micros() - start; |
| 93 | } |
| 94 |
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Index