configuring gpio pin stops LFXO and RTC counter

[butch]

I found that blindly configuring all GPIO pins can stop the LFXO and RTC counter. I am reporting this as: something to be aware of, not obvious to everyone. Not a question, just saying "don't do that, or do it in a different order."

After starting the LFXO clock and enabling RTC counter I did this:

for (uint32_t pin = 0; pin < 32; pin++) {

	// Configure high current output (max 5mA)
	nrf_gpio_cfg(
			pin,
			NRF_GPIO_PIN_DIR_INPUT,
			NRF_GPIO_PIN_INPUT_DISCONNECT,
			NRF_GPIO_PIN_PULLDOWN,
			NRF_GPIO_PIN_H0H1,	// !!! high current
			NRF_GPIO_PIN_NOSENSE);
}

This code changes the pin configurations to have a pulldown and high current, different from their reset condition (but still not connected, same as reset.) Just looking at Figure 1 under GPIO in the product spec, it is not clear to me why this stops the RTC counter. I understand that the physical pin is shared between the LFXO crystal and the GPIO port. I guess that the ANAEN signal is controlled by the LF clock and that somehow configuring the GPIO pin disrupts that.

[RK]

Don't think it has anything to do with ANAEN. You're force driving one of the LFCLK pins low which stops the oscillator which is then going to stop anything using the oscillator. You'd think that when the pin is used for the crystal the GPIO would be disconnected and configuration changes would have no effect, however it seems that's not the case.

You didn't say which chip.

[butch]

I tried to replicate. My code is below. When I step into the code on the debugger, it doesn't complete (infinite loop at the last waitOneTick()) meaning the RTC0 counter has stopped. If I don't step, but just resume the debugger, main() does complete. I don't understand why it behaves differently depending on whether I am single-stepping. The RTC and clocks should still be running while debugging. My environment is Eclipse/GCC ARM/C++.

/*
 * Test whether configuring GPIO pins stops LFXO and RTC0 counter.
 * As alleged in Nordic Devzone thread.
 */

#include "nrf_clock.h"
#include "nrf_rtc.h"
#include "nrf_gpio.h"



unsigned int ticks(){
	return nrf_rtc_counter_get(NRF_RTC0);
}

// spin until RTC0 counter increments at least once
void waitOneTick(){
	unsigned int firstTime, nextTime;

	firstTime = ticks();
	do {
		nextTime = ticks();
	}
	while (nextTime == firstTime);
}

void configureAllGpioPins() {
	for (uint32_t pin = 0; pin < 32; pin++) {

		/*
		 * This configuration is same as POR state except:
		 * 1. high current output (max 5mA) instead of normal
		 * 2. pulldown instead of no pull
		 */
		nrf_gpio_cfg(
				pin,
				NRF_GPIO_PIN_DIR_INPUT,
				NRF_GPIO_PIN_INPUT_DISCONNECT,
				NRF_GPIO_PIN_PULLDOWN,	// !!! pulldown
				NRF_GPIO_PIN_H0H1,	// !!! high current
				NRF_GPIO_PIN_NOSENSE);
	}
}

int main(void)
{
	// configure lf clock source is xtal
	nrf_clock_lf_src_set(NRF_CLOCK_LFCLK_Xtal);

	// start lf clock
	nrf_clock_task_trigger(NRF_CLOCK_TASK_LFCLKSTART);

	// spin until LFXO is stable
	while (! nrf_clock_lf_is_running()) {}

	// RTC0 begin counting (ticks always from LF clock)
	nrf_rtc_task_trigger(NRF_RTC0, NRF_RTC_TASK_START);

	waitOneTick();

	/*
	 * configure all gpio pins
	 * Despite some pins already used by LFXO xtal
	 */
	configureAllGpioPins();

	waitOneTick();
}