nRF52840 DK 3.0.0 device protection is not removed after power up

[Oleh Hordiichuk]

Hello,

I've purchased nRF52840 DK 3.0.0 2022.34 1050279741 and device protection remains after power up, even if I disable it.

Current behaviour:

1. nrfjprog --recover // returns ok
2. nrfjprog --reset // returns ok
// Device is unlocked now and I can flash it
3. Power off & Power on DK
// Device is locked again

The same is happening if I use nrf Connect Programmer.

Expected behaviour:

Device protection removal should remain after power off\power on cycle. 

This is very annoying as I can't debug my firmware properly. How can I disable it completely? 

P.S. my colleague has DK 1.0.0 and nrfjprog --recover works as expected and described in docs.

Kind regards,

Oleh Hordiichuk

[Oleh Hordiichuk]

For those who will face same issue as I: 

It seems I've finally resolved the problem. I tried to write custom firmware which will disable UICR protection, but it didn't help. Finally the working method is:

> nrfjprog -v
nrfjprog version: 10.18.1 external
JLinkARM.dll version: 7.80c

> nrfjprog --recover
Recovering device. This operation might take 30s.
Erasing user code and UICR flash areas.
Writing image to disable ap protect.

Keep attention to the last sentence in nrfjprog --recover: "Writing image to disable ap protect.". If you don't see this sentence, then your version of nrfjprog is not writing small firmware app, which should keep device protection after reboot. So simply update your nrfjprog and it should work!

[Vidar Berg]

Thanks for the update. Yes, version 3.0.0 of the DK comes with the new silicon revision of nrf52840 that has the hardened mechanism described in IN141 Informational Notice v1.1. Disabling approtect on this chip requires that you have an up-to-date version of nrfjprog installed.