nRF52 Flash Protection

[Adam Sillye]

We would like to enable the flash protection for an nRF52 application with the typical scenario:

• to disable flash reads from the JTAG,SWD interface; only erase/reprogram should be possible.
• flash writes from our firmware internally should be enabled.

We went through the infocenter docs and the product spec, but are not sure how exactly to use the UICR register to achieve this. We seen UICR doc and uicr_config.h example, but it's not clear where is 'the bit' to enable the firmware protection. We are not using soft devices, nor DFU.

Are we missing something? There are a lot of articles for nRF51? Are those relevant for nRF52?

[RK]

This is in section 14.1.62 of the product spec, the description for the APPPROTECT register which tells you to write 0x00 to the lowest 8 bits of that register to disable SWD access.

You can do that any way you please, by putting it in the code image, by setting it afterwards with a debugger (thus disabling that debugger from then on) or having the code check and write it the first time it runs.

[Adam Sillye]

Ahh... thank you! :) It's there indeed... We'll put it right in the beginning.

[Adam Varga]

When I write 0xFFFFFF00 to that register and I read it back after that, I get 0x47004800. When I read in the first place I get the reset value (0xFFFFFFFF).

Anyways, I can still read back the whole memory after writing the given values to the APPROTECT register. What do I do wrong?

[RK]

Did you do a reset? The UICR contents is only loaded after a reset. And thinking about it, if UICR counts as flash, you need to enable the NVMC for flash writes before you write it.

[Adam Varga]

That did the trick, thank you so much! For anyone with the same issue: look for NVMC CONFIG register and WEN.