nRF52832 resets ~20 s after entering System OFF (watchdog)

[mento]

We are using nRF52832 with NCS(v2.9.2)/Zephyr and the watchdog (20 s timeout). When the application enters System OFF (e.g. after idle), the device goes to sleep but then resets after about 20 seconds. We see the bootloader and application start again, so it looks like a watchdog reset.
We feed the watchdog before starting the shutdown sequence and before writing the SYSTEMOFF register, but the device still resets about 20 seconds later. We cannot disable the watchdog on nRF52832 (no STOP support).
Question: What is the recommended way to enter System OFF on nRF52832 when the watchdog is enabled, so that the device stays off and is not reset by the watchdog after ~20 seconds?
Thank you.

[Vidar Berg]

Hello,

The WDT cannot run when the device is in System OFF mode, so if you are getting a WDT reset it would indicate that the device did not really enter System OFF mode. Please try to check the RESETREAS register to confirm what the reset source was. Here is an example of a function you can use for reading this register: https://github.com/nrfconnect/sdk-nrf/blob/456f071a6f638b02e4b18819524feeec1d859dbf/samples/nfc/system_off/src/main.c#L158

Note: It is not possible to enter System OFF while the chip is in debug interface mode, see https://docs.nordicsemi.com/bundle/ps_nrf9151/page/chapters/pmu/doc/operationmodes/system_off_mode_emulated.html. That is, you can't be viewing RTT logs or in an active debug session when testing this mode.

Best regards,

Vidar 

[mento]

We want the firmware to enter low‑power sleep (System OFF) and later wake up from a GPIO pin (P0.11).Before entering System OFF, we configure P0.11 as input with no pull and enable SENSE (HIGH or LOW, depending on the current level).Observed behavior

1. Watchdog reset about 20 seconds after requesting sleep (reason unknown)

• In our application, when the firmware decides to go to sleep, it runs a shutdown path that:

• Turns off some peripherals,

• Configures P0.11 as wakeup source using GPIO SENSE,

• Finally writes NRF_POWER->SYSTEMOFF = 1.

• After calling this sleep path, we sometimes see that about 20 seconds later the system is reset by the watchdog.

• We do not know whether:

• The device actually entered System OFF and then somehow resumed incorrectly, or

• It got stuck during/after the shutdown sequence and never reached a stable low‑power state.

• From our point of view the reset reason is “watchdog timeout after trying to enter sleep”, but the root cause is unknown.

2. Sometimes the code path to enter sleep is executed, but changing P0.11 does not wake the device (reason unknown)

• From internal logging we can see that, before sleeping:

• The decision “go to sleep” is taken,

• The shutdown function is called,

• P0.11 is configured as input + NOPULL + SENSE_HIGH/SENSE_LOW,

• NRF_POWER->SYSTEMOFF = 1 is written.

• However, after this, when we change the level on P0.11, the device does not restart and we do not see any new boot behavior.

• This looks like “no GPIO wakeup occurred”, but we cannot tell whether:

• The device never really entered System OFF, or

• It entered System OFF but the GPIO SENSE wakeup on P0.11 did not work.

• Again, the exact reason is unknown.

Questions for Nordic

1. On nRF52832 with NCS v2.9.2, are there any known conditions where, after configuring a GPIO as wake source and writing NRF_POWER->SYSTEMOFF = 1, the device might:

• Fail to actually enter System OFF, or

• Enter System OFF but ignore GPIO SENSE wakeup on that pin?

2. Are there recommended best practices or restrictions for the sequence right before entering System OFF? For example:

• Types of peripheral operations (timers, interrupts, GPIO configuration, etc.) that should be avoided or handled in a specific way before calling SYSTEMOFF,

• Anything that is known to interfere with System OFF or GPIO wakeup if used incorrectly.

3. Given these two symptoms:

• (a) “After calling the sleep path, the system is reset by the watchdog about 20 seconds later (unknown reason)”, and

• (b) “The code to enter System OFF runs, but later changing the GPIO level on P0.11 does not wake the device (unknown reason)”,

do these match any known issues or typical pitfalls when using System OFF + GPIO SENSE wakeup on nRF52832?Any guidance or debugging tips for this kind of System OFF / GPIO wakeup problem would be very helpful.

[mento]

Additionally, when testing with a manual jumper on the wakeup pin, we repeatedly toggle the pin between LOW and HIGH, holding each level for a long time.
Even if the SENSE polarity were initially wrong, we would still expect at least one of these slow transitions to generate an “inactive → active” edge and wake the device.
However, in the problematic firmware, the device never wakes up, which makes us suspect an issue in the System OFF entry/exit behavior rather than just a wrong SENSE configuration.