Modify UICR in application code

[jhc]

Hello, all

I wonder if the UICR can be erased and writed by application code, or only can be programmed by nrfutil tool.

Thank you!

[Edvin]

Hello,

The short answer is "no", but it is actually possible.

Each register in UICR can only be written to once, like the rest of the flash. If you want to write to it again, you need to erase the UICR flash page. The UICR holds some important information, such as the reset pin configuration, and the bootloader address, in addition to the customer registers (which I assume you intend to use).

This means that if you want to update the UICR during runtime, you need to erase the UICR. If you loose power at the wrong time, this means that your device may be bricked. Therefore it is not recommended to update UICR during runtime, although it is physically possible.

If you enable readback protection (APPROTECT), then it is not possible to update the UICR during runtime, because this register is part of the UICR, so you can't turn it off without erasing the entire flash of the nRF.

So what do you intend to use the UICR for? Do you intend to write to it once, or do you intend to update it during the lifetime of the product? If you intend to write to it once, it may be suitable, but if you intend to update it during the runtime, then I would suggest looking into the FDS module instead of using the UICR.

Best regards,

Edvin

[RMV]

On the NRF52832 the product specification states that the UICR registers are 0xFFFFFFFF when erased but users can always write a 0 to any bit (other than the 'maximum number of writes before erase' requirement).

If all that the user wants is to write a '0' then I do not see the need to erase the full UICR page.

Is that correct?

[Edvin]

That is correct. As mentioned, you can write to it once (actually, as you say, "maximum number of writes before erase"). But if you want to update a value that already is written, so that you need to flip a 0 to a 1, then you need to erase the entire UICR, as described below. When doing this, you may loose some important information, such as the reset pin registers, and the bootloader address.

Best regards,

Edvin