Improving delay()

[mikaelpatel]

The current implementation only calls yield() once (https://github.com/arduino/ArduinoCore-avr/blob/master/cores/arduino/wiring.c#L106)

void delay(unsigned long ms)
{
	uint32_t start = micros();

	while (ms > 0) {
		yield();
		while ( ms > 0 && (micros() - start) >= 1000) {
			ms--;
			start += 1000;
		}
	}
}

Could be improved to something like:

void delay(unsigned long ms)
{
	uint32_t start = micros();
	while ( ms > 0 && (micros() - start) >= 1000) {
		yield();
		ms--;
		start += 1000;
	}
}

Also adding the attribute "weak" could allow redefinition when needed, e.g. allow support for low power mode in Cooperative Scheduler, https://github.com/mikaelpatel/Arduino-Scheduler

void delay(unsigned long ms) __attribute__ ((weak));

[cmaglie]

Looks like the "improved" version will never enter the while loop because (micros() - start) >= 1000 can not be true?

[mikaelpatel]

@cmaglie My bad. Got confused over the two while-loops. Sorry about that.

There was a second request which actually is more "urgent"; making delay() a weak definition so that it could be redefined as yield() allows. I would like to add a low-power mode to my Scheduler library (when all tasks are in delay()).