PulseIn function

Projects Programming
1

Hey everyone,

I have a project with a LM555 timer and need to calculate how much time it takes for an input to go from LOW to HIGH and then to LOW again.

Basically, I want to know the period of a square wave generated by the LM555 timer.

I did it with Arduino using the function Pulseln. But I need to do this using a Beaglebone and programming in C++ (Using QtCreator).

Is there a way to "open" the function PulseIn so I know what it does? Moreover, do you guys have any piece of code that might help me?

Thank you in advance.

2

In my version (1.6.9), the function is located in \hardware\arduino\avr\cores\arduino\wiring_pulse.c

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
	// digitalRead() instead yields much coarser resolution.
	uint8_t bit = digitalPinToBitMask(pin);
	uint8_t port = digitalPinToPort(pin);
	uint8_t stateMask = (state ? bit : 0);

	// convert the timeout from microseconds to a number of times through
	// the initial loop; it takes approximately 16 clock cycles per iteration
	unsigned long maxloops = microsecondsToClockCycles(timeout)/16;

	unsigned long width = countPulseASM(portInputRegister(port), bit, stateMask, maxloops);

	// prevent clockCyclesToMicroseconds to return bogus values if countPulseASM timed out
	if (width)
		return clockCyclesToMicroseconds(width * 16 + 16);
	else
		return 0;
}
3

Thank you for the answer Saximus. I took a look at the expanded function you have sent, but it uses many of other arduino "built-in" functions.

As I need to write a brand new code in C++, it serves as reference but still there are some blanks to fill.

Regards,

4

But I need to do this using a Beaglebone and programming in C++

What did the guys at the Beaglebone forum say?

5

Unfortunatelly I didn't get any answers from them.