nRF52832 does not wake up on event using __WFE

[eBrock]

nRF52832 doesn't seem to wake up when an event is generated. I confirmed that the RTC0 is active and the event is generated

upon COMPARE[0] match using the SES debugger. But nothing happens when the RTC0 generates the event. Sleep current is

about 3.5 uA. I can see the current going from about 5.7 mA down to 3.5 uA after 2s delay (following program code). I have read

in another post that the micro should wake up from an event firing, but that doesn't seem to be happening. I'm probably missing

something. Any help is greatly appreciated.

Nordic SDK 15.3.0

SES v4.22

#include <stdbool.h>
#include <stdint.h>
#include <string.h>
#include "nrf.h"
#include "nrf_delay.h"
#include "nrf_gpio.h"

#define LED_1          17


void hf_clock_start( void )
{
    // Start HFCLK and wait for it to start.
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_HFCLKSTART = 1;
    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
    nrf_delay_ms(1);
}


void lf_clock_start( void )
{
    // Start LFCLK and wait for it to start.
    NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
    NRF_CLOCK->TASKS_LFCLKSTART = 1;
    while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0);
    nrf_delay_ms(1);
}


void gpio_init( void )
{
    nrf_gpio_cfg_output(LED_1);
    nrf_gpio_pin_write(LED_1, 0);

}


void rtc_init( void )
{
    NRF_RTC0->PRESCALER = 0x0;
    NRF_RTC0->CC[0] = 0x10001;
    NRF_RTC0->EVTEN = 0x10000;
    NRF_RTC0->TASKS_CLEAR = true;
    NRF_RTC0->TASKS_START = true;
    nrf_delay_ms(1);
}


void low_power_sleep( void )
{
    NRF_RTC0->TASKS_CLEAR = true;
    NRF_RTC0->EVENTS_COMPARE[0] = 0;
    __WFE();
}


int main(void)
{
    hf_clock_start();
    lf_clock_start();
    gpio_init();
    rtc_init();


    while (true)
    {
        nrf_delay_ms(2000);
        NRF_CLOCK->TASKS_HFCLKSTOP = true;
        nrf_gpio_pin_toggle(LED_1);
        low_power_sleep();
        hf_clock_start();
        nrf_gpio_pin_toggle(LED_1);
    }
}

[Vidar Berg]

Hi,

The EVENT register must be connected to the NVIC to raise a system event and wake the CPU. The connections are as you may have seen illustrated in Figure 4 in Event control feature. So you would need to enable COMPARE0 interrupt and the RTC0 IRQ in the NVIC. Is the goal to trigger wakeup without an interrupt service routine for the RTC0 IRQ?

   

[eBrock]

Yes, the goal is to trigger a wakeup without an interrupt service routine. I assume that when the CPU wakes, it will continue code execution after the __WFE call?

[Vidar Berg]

Yes, on wakeup the CPU will continue execution after the __WFE call. You may try to enable SEVONPEND (SCB->SCR |= SCB_SCR_SEVONPEND_Msk;) in your startup code to make the CPU wake on pending interrupts. Alternatively, replace it with the __WFI instruction which always wakes up on pending interrupts. Then mask the interrupt around the WFE/WFI instruction with PRIMASK or BASEPRI so the interrupt stays pending. The pending bit would also need to be cleared after wakeup since the ISR is not being performed. 

If you implement something like I described above, please make sure to review and test it thoroughly to ensure that there aren't any potential race conditions that could cause the CPU to sleep forever. 

[eBrock]

Thanks for your support. I now have the CPU waking up. I tried with and without the SEVONPEND enabled and it still wakes up. The only problem now is that I need an interrupt handler. The code stops executing when the interrupt fires and it lands on the dummy handler in the SES startup routines.

I think I'm good to go now, but here is the code change for reference:

void rtc_init( void )
{
    //SCB->SCR |= SCB_SCR_SEVONPEND_Msk;
    NRF_RTC0->PRESCALER = 0x0;
    NRF_RTC0->CC[0] = 0x10001;
    NRF_RTC0->INTENSET = 0x10000;
    NRF_RTC0->TASKS_CLEAR = true;
    NRF_RTC0->TASKS_START = true;
    NVIC_EnableIRQ(RTC0_IRQn);
    nrf_delay_ms(1);
}

[Vidar Berg]

No problem. Glad to hear that you got it to work. SEVONPEND is only needed if you want to wake the CPU while the interrupt is masked with PRIMASK or BASEPRI (ie temporarily disabled). But I think it's better to use the interrupt handler.

e.g.,

void RTC0_IRQHandler (void)

{ 

    NRF_RTC0->EVENTS_COMPARE[0] = 0;

} 

[eBrock]

I changed to using __WFI as it seems to work best for my application.

Here is current code for the sleep functionality:

void RTC0_IRQHandler( void )
{
    NRF_RTC0->TASKS_CLEAR = true;
    NRF_RTC0->EVENTS_COMPARE[0] = 0;
}

void rtc_init( void )
{
    NRF_RTC0->PRESCALER = 0x0;
    NRF_RTC0->CC[0] = 0x10001;
    NRF_RTC0->TASKS_CLEAR = true;
    NRF_RTC0->TASKS_START = true;
    NVIC_EnableIRQ(RTC0_IRQn);
    nrf_delay_ms(1);
}

void low_power_sleep( void )
{
    NRF_RTC0->INTENSET = 0x10000;
    NRF_RTC0->TASKS_CLEAR = true;
    NRF_RTC0->EVENTS_COMPARE[0] = 0;
    __WFI();
    NRF_RTC0->INTENSET = 0x00000;
}