1 | /*
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2 | Copyright (c) 2011 Arduino. All right reserved.
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3 |
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4 | This library is free software; you can redistribute it and/or
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5 | modify it under the terms of the GNU Lesser General Public
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6 | License as published by the Free Software Foundation; either
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7 | version 2.1 of the License, or (at your option) any later version.
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8 |
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9 | This library is distributed in the hope that it will be useful,
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10 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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12 | See the GNU Lesser General Public License for more details.
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13 |
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14 | You should have received a copy of the GNU Lesser General Public
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15 | License along with this library; if not, write to the Free Software
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16 | Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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17 | */
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18 |
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19 | #include "Arduino.h"
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20 | #include "wiring_private.h"
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21 | #include "wiring_pulse.h"
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22 | /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
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23 | * or LOW, the type of pulse to measure. Works on pulses from 2-3 microseconds
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24 | * to 3 minutes in length, but must be called at least a few dozen microseconds
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25 | * before the start of the pulse. */
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26 | extern uint32_t pulseIn( uint32_t pin, uint32_t state, uint32_t timeout )
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27 | {
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28 | // cache the port and bit of the pin in order to speed up the
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29 | // pulse width measuring loop and achieve finer resolution. calling
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30 | // digitalRead() instead yields much coarser resolution.
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31 | PinDescription p = g_APinDescription[pin];
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32 | uint32_t width = 0; // keep initialization out of time critical area
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33 |
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34 | // convert the timeout from microseconds to a number of times through
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35 | // the initial loop; it takes 22 clock cycles per iteration.
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36 | uint32_t numloops = 0;
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37 | uint32_t maxloops = microsecondsToClockCycles(timeout) / 22;
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38 | // wait for any previous pulse to end
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39 | while (digitalRead(pin) == state)
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40 | if (numloops++ == maxloops)
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41 | return 0;
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42 |
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43 |
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44 | // wait for the pulse to start
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45 | while (digitalRead(pin) != state)
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46 | if (numloops++ == maxloops)
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47 | return 0;
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48 |
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49 | // wait for the pulse to stop
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50 | while (digitalRead(pin) == state) {
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51 | if (numloops++ == maxloops)
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52 | return 0;
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53 | width++;
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54 | }
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55 |
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56 | // convert the reading to microseconds. The loop has been determined
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57 | // to be 52 clock cycles long and have about 16 clocks between the edge
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58 | // and the start of the loop. There will be some error introduced by
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59 | // the interrupt handlers.
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60 | return clockCyclesToMicroseconds(width * 52 + 16);
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61 | }
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