diff options
Diffstat (limited to 'cores/arduino/wiring_pulse.c')
| -rwxr-xr-x | cores/arduino/wiring_pulse.c | 20 |
1 files changed, 13 insertions, 7 deletions
diff --git a/cores/arduino/wiring_pulse.c b/cores/arduino/wiring_pulse.c index 642a5a2..0157114 100755 --- a/cores/arduino/wiring_pulse.c +++ b/cores/arduino/wiring_pulse.c @@ -26,10 +26,10 @@ #include "pins_arduino.h" /* 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 10 microseconds - * to 3 minutes in length, but must be called at least N microseconds before - * the start of the pulse. */ -unsigned long pulseIn(uint8_t pin, uint8_t state) + * 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. */ +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 // pulse width measuring loop and achieve finer resolution. calling @@ -39,17 +39,23 @@ unsigned long pulseIn(uint8_t pin, uint8_t state) 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. + unsigned long numloops = 0; + unsigned long maxloops = microsecondsToClockCycles(timeout) / 16; + // 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) width++; // convert the reading to microseconds. The loop has been determined - // to be 10 clock cycles long and have about 12 clocks between the edge + // to be 10 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 * 10 + 12); + return clockCyclesToMicroseconds(width * 10 + 16); } |