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pulseIn: modify function to use ASM implementation

This commit is contained in:
Martino Facchin 2015-03-02 13:33:50 +01:00
parent 2bac15c63d
commit 6940c1d644
2 changed files with 14 additions and 29 deletions
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2
cores/arduino/wiring_private.h
View File

@ -43,6 +43,8 @@ extern "C"{
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif
uint32_t countPulseASM(volatile uint8_t *port, uint8_t bit, uint8_t stateMask, unsigned long maxloops);
#define EXTERNAL_INT_0 0
#define EXTERNAL_INT_1 1
#define EXTERNAL_INT_2 2

41
cores/arduino/wiring_pulse.c
View File

@ -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.
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++;
}
// 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);
}
// convert the timeout from microseconds to a number of times through
// the initial loop; it takes approximately 16 clock cycles per iteration
unsigned long numloops = 0;
unsigned long maxloops = microsecondsToClockCycles(timeout)/16;
width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops);
return clockCyclesToMicroseconds(width * 16 + 16);
}