Unable to configure secure area on H735

[Benedikt Schmidt]

I'm trying to configure a secure area (HDP) for a H735. To do so, I am following the steps described in AN5601 HDP secure area for STM32H7B3xx microcontrollers using the examples HDP_Appli and HDP_Boot for the STM32H735G-DK. The application note does not reference the H735 explicitly, but the steps seem to be the same according to the reference manual of the H735.

As soon as I configure the secure area start and end the values do not get written into the option bytes. I already implemented these steps in code and it looks like the call to HAL_FLASH_OB_Launch fails with a OPTCHANGEERR. I already verified that at this point the security bit is set, both while following the steps manually using the Cube Programmer, as well as also while doing it from the application code itself. Before I set the secure area start and end values they are configured with start > end, hence no secure are should be active. In fact, I have always the initial values start = 0x0ff and end = 0x000, as I am unable to change them to anything else.

I would be very glad if somebody could help me out, as I am running a little bit out of ideas.

Regards,

Benedikt

[Benedikt Schmidt]

An Upgrade of the Cube Programmer from 2.7 to 2.9 (which came out a few days ago) solved the issue with the example projects. Therefore, I should probably also be able to do this in my application code. Although I am still uncertain what I am doing wrong. Is for instance the power down between activating the security bit and configuring the secure area really necessary? Would also a reset be sufficient?

Regards,

Benedikt