Timer Interrupts on Due

Hardware Arduino Due
57

Nice library - thank you for sharing it.

One idea: it would be nice if startTimer() picked the clock source with the least error, given the desired frequency (credit for this idea goes to RCArduino - see comments in RCArduino: Arduino Due DDS - Part 1 - Sinewaves and Fixed Point Maths).

I hacked together some code to demonstrate it. Caveat: I'm an arduino newb.

/*
 * pick clock that provides the least error for specified frequency.
 */
uint8_t pickClock(uint32_t frequency, uint32_t& retRC)
{
	/*
	Timer		Definition
	TIMER_CLOCK1	MCK/2
	TIMER_CLOCK2	MCK/8
	TIMER_CLOCK3	MCK/32
	TIMER_CLOCK4	MCK/128
	*/

	struct {
		uint8_t flag;
		uint8_t divisor;
	} clockConfig[] = {
		{ TC_CMR_TCCLKS_TIMER_CLOCK1, 2 },
		{ TC_CMR_TCCLKS_TIMER_CLOCK2, 8 },
		{ TC_CMR_TCCLKS_TIMER_CLOCK3, 32 },
		{ TC_CMR_TCCLKS_TIMER_CLOCK4, 128 }
	};

	int clkId = 3;
	int bestClock = 3;
	float bestError = 1.0;

	do {
		float ticks = (float) VARIANT_MCK / (float) frequency / (float) clockConfig[clkId].divisor;
		float error = abs(ticks - round(ticks));
		if (abs(error) < bestError) {
			bestClock = clkId;
			bestError = error;
		}
	} while (clkId-- > 0);

	float ticks = (float) VARIANT_MCK / (float) frequency / (float) clockConfig[bestClock].divisor;
	retRC = (uint32_t) round(ticks);
	return clockConfig[bestClock].flag;
}

void startTimer(Tc *tc, uint32_t channel, IRQn_Type irq, uint32_t frequency, volatile void (*function)())
{
	pmc_set_writeprotect(false);
	pmc_enable_periph_clk((uint32_t)irq);

	uint32_t rc = 0;
	uint8_t clock = pickClock(frequency, rc);
	TC_Configure(tc, channel, TC_CMR_WAVE | TC_CMR_WAVSEL_UP_RC | clock);

	... remainder of startTimer() unchanged ...

}