Can I enter DFU from WDT ?

[Roger Clark]

Is it possible to enter DFU / OTA from a DWT

i.e if the code crashes, and I can't trigger DFU mode by writing to a characteristic, can the WDT jump straight to the DFU / OTA ?

[Nguyen Hoan Hoang]

DFU always get executed at reset so technically yes. The thing is dfu will check for valid App and jump right to it immediately so you'll end up in a jumping loop. You can have the DFU stay in DFU mode by holding a button when DFU is booting. If you don't have a button then you need to modify the DFU code to stay in DFU for a certain amount of seconds before booting the App. That would give a chance to reflash.

[Roger Clark]

OK.

I have a button, but I was hoping to have some sort of buttonless method, as it may not be easy to get to the device to press the button.

I'll need to read the buttonless source code and see how it manages.

(On other processors I use, they have some internal registers that survive a reset, which can be used to lock the code into upload mode, but I don't know if the nRF52 does it that way, or some other way)

[Hung Bui]

Hi Roger,

You may need to write to flash before you let the WDT trigger a reset. The retained register GPREGRET is reset when WDT. If you have a look at the buttonless example in SDK v12, we write to flash before we trigger a reset, you can use that example and WDT to enter DFU bootloader. In SDK v13, we switch to GPREGRET instead.

[Roger Clark]

OK Thanks.

I'm using SDK 11 SD132, I can probably switch to SDK 12. I'm not sure about 13 I think it still has some problems