8f1711f7cc
Add 'const' declaration to avoid:
cores/arduino/pulse.c: In function 'pulseIn':
cores/arduino/pulse.c:44:29: warning: initialization discards
'const' qualifier from pointer target type [enabled by default]
volatile uint32_t *port = &(PORT->Group[p.ulPort].IN.reg);
^
83 lines
3.2 KiB
C
83 lines
3.2 KiB
C
/*
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Copyright (c) 2015 Arduino LLC. All right reserved.
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library 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.
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See the GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with this library; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <Arduino.h>
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// See pulse_asm.S
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extern unsigned long countPulseASM(const volatile uint32_t *port, uint32_t bit, uint32_t stateMask, unsigned long maxloops);
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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 2-3 microseconds
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* to 3 minutes in length, but must be called at least a few dozen microseconds
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* before the start of the pulse. */
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uint32_t pulseIn(uint32_t pin, uint32_t state, uint32_t timeout)
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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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PinDescription p = g_APinDescription[pin];
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uint32_t bit = 1 << p.ulPin;
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uint32_t stateMask = state ? bit : 0;
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#if defined(__SAMD51__)
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/*
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* The SAMD51 is fast enough to use really obvious code (similar to
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* what was used to produce pulse_asm.S, but using micros() for timing.
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* No assembly required, no conversion of loop counts to times (which is
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* worrisome in the presence of cache.)
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*/
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const volatile uint32_t *port = &(PORT->Group[p.ulPort].IN.reg);
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uint32_t usCallStart; // microseconds at start of call, for timeout.
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uint32_t usPulseStart; // microseconds at start of measured pulse.
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usCallStart = usPulseStart = micros();
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// wait for any previous pulse to end
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while ((*port & bit) == stateMask) {
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if (micros() - usCallStart > timeout)
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return -1;
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}
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// wait for the pulse to start
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while ((*port & bit) != stateMask) {
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usPulseStart = micros();
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if (usPulseStart - usCallStart > timeout)
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return -2;
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}
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// wait for the pulse to stop
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while ((*port & bit) == stateMask) {
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if (micros() - usCallStart > timeout)
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return -3;
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}
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return micros() - usPulseStart;
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#else
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// convert the timeout from microseconds to a number of times through
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// the initial loop; it takes (roughly) 13 clock cycles per iteration.
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uint32_t maxloops = microsecondsToClockCycles(timeout) / 13;
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uint32_t width = countPulseASM(&(PORT->Group[p.ulPort].IN.reg), bit, stateMask, maxloops);
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// convert the reading to microseconds. The loop has been determined
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// to be 13 clock cycles long and have about 16 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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if (width)
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return clockCyclesToMicroseconds(width * 13 + 16);
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else
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return 0;
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#endif // SAMD51
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}
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