pulseIn: modify function to use ASM implementation
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@ -43,6 +43,8 @@ extern "C"{
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#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
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#endif
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uint32_t countPulseASM(volatile uint8_t *port, uint8_t bit, uint8_t stateMask, unsigned long maxloops);
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#define EXTERNAL_INT_0 0
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#define EXTERNAL_INT_1 1
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#define EXTERNAL_INT_2 2
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@ -28,7 +28,10 @@
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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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* before the start of the pulse.
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*
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* This function performs better with short pulses in noInterrupt() context
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*/
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unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long 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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@ -38,32 +41,12 @@ unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout)
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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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// convert the timeout from microseconds to a number of times through
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// the initial loop; it takes 16 clock cycles per iteration.
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unsigned long numloops = 0;
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unsigned long maxloops = microsecondsToClockCycles(timeout) / 16;
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// wait for any previous pulse to end
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while ((*portInputRegister(port) & bit) == stateMask)
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if (numloops++ == maxloops)
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return 0;
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// wait for the pulse to start
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while ((*portInputRegister(port) & bit) != stateMask)
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if (numloops++ == maxloops)
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return 0;
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// wait for the pulse to stop
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while ((*portInputRegister(port) & bit) == stateMask) {
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if (numloops++ == maxloops)
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return 0;
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width++;
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}
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// convert the reading to microseconds. The loop has been determined
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// to be 20 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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return clockCyclesToMicroseconds(width * 21 + 16);
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}
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// convert the timeout from microseconds to a number of times through
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// the initial loop; it takes approximately 16 clock cycles per iteration
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unsigned long numloops = 0;
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unsigned long maxloops = microsecondsToClockCycles(timeout)/16;
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width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops);
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return clockCyclesToMicroseconds(width * 16 + 16);
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}
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