NRF52 Watchdog Reset When only reset source is soft reset?

[CurtisHx]

I'm working on a battery - operated device where the battery is soldered onto the device, which makes it inconvenient to pull power to the device. I might be able to get to the reset pin on the nRF52, but that's unlikely.

Is there any way (documented, undocumented, whatever) that I can use to reset and reconfigure the WDT besides Pin, Brownout, or Power? I can't pull power and the batteries are designed to last 4+ year. We don't use the pin to reset the chip when programming. We use the SWD reset command, which is interpreted by the NRF52 as a reset.

Are there any options or am I just completely boned here?

[Hung Bui]

@Curtis: What about letting the WDT resets itself ? You can write something to the retention register to tell the chip the next time it wakes up that the reset was on purpose and can reconfigure the WDT.

[CurtisHx]

It looks like that's pretty much my only option at this point. It's not a great option because we have to run the CPU while waiting for the WDT to expire (increased current consumption), plus it causes one of those "WFT?" moments in the code. If I was looking for the spot in the code that triggers a system reset, I'd be initially looking for "NVIC_SystemReset()"

[Hung Bui]

I'm not sure why you need to keep the CPU awake ?

But I agree it maybe not the cleanest way. I don't think any other WDT implementation would allow you to bypass it and reset it without a full hardware reset.

[CurtisHx]

If you configured the WDT to not run while the CPU is asleep (WDT->CONFIG->SLEEP set to 0), then you can't go to sleep while waiting for the WDT to expire because the WDT won't run (which is how we have our WDT configured).

There's a couple of different options for future designs of the WDT:

1. Provide an unlock sequence to allow WDT reconfiguration without a reset. Something like "you have to write 0x24 0x44 0x66 0xBE 0x81 in that exact order to the UNLOCK register to reconfigure the WDT"

or

2. Reset the WTD as part of a soft reset.

[Hung Bui]

Hi Curtis,

Thanks for your suggestions.

If you are using that mode WDT->CONFIG->SLEEP set to 0, please be aware of PAN #88 here.