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STM32 RDP2 prevents the modification of OPTLOCK?

ppj
Associate

‎2019-05-14 05:21 AM

Hi everyone,

we have a bootloader that writes new application code to the flash bank 2 in an STM32H7 and afterwards swaps the banks to execute the new code. The procedure for swapping is something like this:

   unlock OPTLOCK

   set SWAP_BANK_OPT

   set OPTSTART

   lock OPTLOCK

   system reset

This works fine with a Level 0 readout protection (RDP). However it is not working with a RDP level 2.

The reference manual states that only the SWAP_BANK_OPT bit is adjustable when RDP2 is set. It also states that you have to unlock OPTLOCK before changing SWAP_BANK_OPT.

Does this mean if OPTLOCK is set (locked) when RDP2 is active you can not change SWAP_BANK_OPT since you can not modfiy OPTLOCK?

So the solution to use SWAP_BANK_OPT would be to unlock OPTLOCK before activating RDP2?

Is there any other reason that would prevent IAP when RDP2 is set?

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After Forever
Lead

‎2019-05-14 05:40 AM

RM doesn't mention any relation (that I can find) between RDP level 2 and OPTLOCK.

OPTLOCK should be unlockable in any level or RDP.

Are you sure you are following the correct procedure?

[Cick Show More]

From RM0433:

To change the SWAP_BANK bit (for example to apply a new firmware update), respect the sequence below:

  1. Unlock OPTLOCK bit, if not already unlocked.
  2. Set the new desired SWAP_BANK_OPT value in the FLASH_OPTSR_PRG register.
  3. Start the option byte change sequence by setting the OPTSTART bit in the FLASH_OPTCR register.
  4. Once the option byte change has completed, FLASH_OPTSR_CUR contains the expected SWAP_BANK_OPT value, but SWAP_BANK bit in FLASH_OPTCR has not yet been modified and the bank swapping is not yet effective.
  5. Force a system reset or a POR. When the reset rises up, the bank swapping is effective (SWAP_BANK value updated in FLASH_OPTCR) and the new firmware shall be executed.

The SWAP_BANK bit in FLASH_OPTCR is read-only and cannot be modified by the application software.

The SWAP_BANK_OPT option bit in FLASH_OPTSR_PRG can be modified whatever the RDP level (i.e. even in level 2), thus allowing advanced firmware upgrade in any level of readout protection.

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After Forever
Lead

‎2019-05-14 05:44 AM

Also, the errata describes an issue with bank swapping for revision Y parts. Make sure you are not affected.

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