nRF52 wakeup time

[tmav123]

Hi,

what is the typical or max wake up time of the nRF52 from the RTC or GPIOTE irq (when configured as sense for low level input)?

In my setup, I see a wakeup time of ~13usec from the moment that the nRF52 current consumption is increasing, till the time the RTC irq handler is running.

RTC is running from an external crystal.

Normally I would expect the following wakeup delays till the start of RTC irq handler:

tSTART_HFINT Startup time: 3us

tIDLE2CPU Time from IDLE to CPU execute: 3us

What is the reason that I see 13us and not 6us till the RTC handler starts to execute code?

The wakup time from an external GPIO sense low event that I measure is ~16us.

Regards

Thanassis

[Simonr]

Hi

What is causing the extra time before the IRQ handler kicks in is likely that the GPIO driver causes some delay going through overheads. You can try writing to NRF_GPIO directly instead, to avoid any unnecessary calls. The nRF goes to sleep as soon as it is done, but you are measuring over a decoupling capacitor, which holds on to the voltage for some time, which is why you see the curve.

I suggest you take a look at the PPI, as I suspect it may suit your application, seeing as it doesn't depend on the CPU. I don't know which chip you are using so I attached the link to the nRF52840 PPI, if you want to use it please make sure to read the correct PS.

Best regards,

Simon

[tmav123]

Hi,

the CPU that I use is the nRF52832_xxAA.

I will try to write direct to the NRF_GPIO to see if it has any measurable effect.

I think your suggestion to use the NRF_GPIOTE->EVENTS_PORT and feed it to the

PPI to toggle a GPIO pin, it will show the accurate wakeup timing.

I will let you know about the results.

Best Regards

Thanassis

[tmav123]

Hi,

using the PPI & GPIOTE to set a pin output, shows that the nRF52 is setting the output 3us after the wakeup pulse.

The time for the GPIOTE irq handler to kick is ~12us.

The code used to set the pin output from the GPIOTE PORT event is:

    // ppi init - connect GPIOTE irq event to the GPIO_PPI_IRQ_PIN 
    nrf_ppi_channel_endpoint_setup(NRF_PPI_CHANNEL0, (uint32_t)&NRF_GPIOTE->EVENTS_PORT, (uint32_t)&NRF_GPIOTE->TASKS_SET[0]);
    nrf_ppi_channel_enable(NRF_PPI_CHANNEL0);
    
    // configure PPI GPIOTE pin
    nrf_gpiote_event_configure(0, GPIO_PPI_IRQ_PIN, NRF_GPIOTE_POLARITY_LOTOHI);
    nrf_gpiote_task_enable(0);

Best Regards

Thanassis