50 lines
1.9 KiB
C
50 lines
1.9 KiB
C
/*
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* Copyright (c) 2005-2006 David A. Mellis
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Lesser General Public License as published by
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* the Free Software Foundation, either version 2.1 of the License, or
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* (at your option) any later version.
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "wiring_private.h"
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#include "pins_waspmote.h"
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/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
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* or LOW, the type of pulse to measure. Works on pulses from 10 microseconds
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* to 3 minutes in length, but must be called at least N microseconds before
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* the start of the pulse. */
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unsigned long pulseIn(uint8_t pin, uint8_t state)
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{
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// cache the port and bit of the pin in order to speed up the
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// pulse width measuring loop and achieve finer resolution. calling
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// digitalRead() instead yields much coarser resolution.
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uint8_t bit = digitalPinToBitMask(pin);
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uint8_t port = digitalPinToPort(pin);
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uint8_t stateMask = (state ? bit : 0);
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unsigned long width = 0; // keep initialization out of time critical area
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// wait for the pulse to start
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while ((*portInputRegister(port) & bit) != stateMask)
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;
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// wait for the pulse to stop
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while ((*portInputRegister(port) & bit) == stateMask)
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width++;
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// convert the reading to microseconds. The loop has been determined
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// to be 10 clock cycles long and have about 12 clocks between the edge
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// and the start of the loop. There will be some error introduced by
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// the interrupt handlers.
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return clockCyclesToMicroseconds(width * 10 + 12);
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}
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