Sleep mode and RTC

[frank zhang]

Hello, I am working on NRF52 DK,SDK12.1.0. When I am trying to make board into sleep mode with sleep_mode_enter(I have get sd_power_system_off),I found that RAM/UART is still working, I am not sure if the CPU enter sleep mode. My requirement is make CPU and all peripheral not working but RTC2 working continuously,so that I can save power and keep the time. Can I achieve this?

[Susheel Nuguru]

If your UART is still working then the system is not in SYSTEMOFF mode. RTC is not powered in systemoff (meaning your RTC is not running in system off), only resources available are given below.

System OFF is the deepest power saving mode the system can enter. In this mode, the system’s core functionality is powered down and all ongoing tasks are terminated. The only mechanism that is functional and responsive in this mode is the reset and the wakeup mechanism.

The system can be woken up from System OFF mode either from the DETECT signal (when active) generated by the GPIO peripheral, by the ANADETECT signal (when active) generated by the LPCOMP module, or from a reset. When the system wakes up from OFF mode, a system reset is performed.

[frank zhang]

Hi Aryan， Thanks for your fast feedback. I did not want to enter system OFF mode. I just want system sleep and keep RTC time. Thanks

[Susheel Nuguru]

then instead of calling sd_power_systemoff, you need to call

static void power_manage(void)
{
    uint32_t err_code = sd_app_evt_wait();

    APP_ERROR_CHECK(err_code);
}

like below from your main loop.

for (;;)
{        
    power_manage();
}

[frank zhang]

Hi Aryan, You mean we just need call power_manage(),the system will go to SYSTEM ON sleep mode automaticly when no task running, and if some interrupt occured, the system will wake up immediately, right? Does NRF52 have deep sleep mode (CPU and most peripheral not working) and only keep RTC running. Thanks

[Susheel Nuguru]

You mean we just need call power_manage(),the system will go to SYSTEM ON sleep mode automaticly when no task running, and if some interrupt occured, the system will wake up immediately, right?

Right.

Does NRF52 have deep sleep mode (CPU and most peripheral not working) and only keep RTC running.

No, in Deep Sleep, called SYSTEMOFF, RTC will also be powered OFF. Only few registers retain their value. For that please look into Retained registers section in POWER chapter in the Reference Manual of the chip