changing timeout function of pulseIn()

Forum 2005-2010 (read only) Software Syntax & Programs
#1

Hi folks, I'd like to change the timeout function of pulseIn().

The change I'd like to make is: AFTER going HIGH wait for echo to return, give up and return 0 if no echo has returned within the specified timeout. I tried to do that myself modifying the pulseIn() source code, but unfortunately have not succeeded yet. I attached it here. Any ideas?

#include "wiring_private.h"
#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 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) 
// uint8_t its shorthand for: a type of unsigned integer of length 8 bits 



{
      // cache the port and bit of the pin in order to speed up the
      // pulse width measuring loop and achieve finer resolution.  calling
      // digitalRead() instead yields much coarser resolution.
      uint8_t bit = digitalPinToBitMask(pin);
      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)
            width++;

      // convert the reading to microseconds. The loop has been determined
      // 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 + 16); 
}
#2

The timeout is “transformed” to maxloops. In the function there are three while loops from which two testing maxloop reached. Have a look at code below:

However note that the 3rd timemeasuring loop has been altered so the width to Microseconds formula (width *10 +16) must be recallibrated.

#include "wiring_private.h"
#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 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)
// uint8_t its shorthand for: a type of unsigned integer of length 8 bits



{
      // cache the port and bit of the pin in order to speed up the
      // pulse width measuring loop and achieve finer resolution.  calling
      // digitalRead() instead yields much coarser resolution.
      uint8_t bit = digitalPinToBitMask(pin);
      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)
        {
            width++;
[glow]                     if (numloops++ == maxloops)
                {
                  return 0;
                }[/glow]
        }

      // convert the reading to microseconds. The loop has been determined
      // 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 + 16); [glow] <== needs change[/glow]
}
#3