diff options
Diffstat (limited to 'cores/arduino/wiring_pulse.c')
| -rw-r--r-- | cores/arduino/wiring_pulse.c | 37 |
1 files changed, 10 insertions, 27 deletions
diff --git a/cores/arduino/wiring_pulse.c b/cores/arduino/wiring_pulse.c index 0d96886..2ac6988 100644 --- a/cores/arduino/wiring_pulse.c +++ b/cores/arduino/wiring_pulse.c @@ -28,7 +28,10 @@ /* Measures the length (in microseconds) of a pulse on the pin; state is HIGH * or LOW, the type of pulse to measure. Works on pulses from 2-3 microseconds * to 3 minutes in length, but must be called at least a few dozen microseconds - * before the start of the pulse. */ + * before the start of the pulse. + * + * This function performs better with short pulses in noInterrupt() context + */ unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout) { // cache the port and bit of the pin in order to speed up the @@ -38,32 +41,12 @@ unsigned long pulseIn(uint8_t pin, uint8_t state, unsigned long timeout) uint8_t port = digitalPinToPort(pin); uint8_t stateMask = (state ? bit : 0); unsigned long width = 0; // keep initialization out of time critical area - + // convert the timeout from microseconds to a number of times through - // the initial loop; it takes 16 clock cycles per iteration. + // the initial loop; it takes approximately 16 clock cycles per iteration unsigned long numloops = 0; - unsigned long maxloops = microsecondsToClockCycles(timeout) / 16; - - // wait for any previous pulse to end - while ((*portInputRegister(port) & bit) == stateMask) - if (numloops++ == maxloops) - return 0; - - // wait for the pulse to start - while ((*portInputRegister(port) & bit) != stateMask) - if (numloops++ == maxloops) - return 0; - - // wait for the pulse to stop - while ((*portInputRegister(port) & bit) == stateMask) { - if (numloops++ == maxloops) - return 0; - width++; - } + unsigned long maxloops = microsecondsToClockCycles(timeout)/16; - // convert the reading to microseconds. The loop has been determined - // to be 20 clock cycles long and have about 16 clocks between the edge - // and the start of the loop. There will be some error introduced by - // the interrupt handlers. - return clockCyclesToMicroseconds(width * 21 + 16); -} + width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops); + return clockCyclesToMicroseconds(width * 16 + 16); +}
\ No newline at end of file |