How to write non-reserved option bytes on STM32H750xx MCU?

[briankaz]

Hello!

The STM32H750xx data sheet states that the MCU has 2KB of space in flash memory for "option bytes." However, the programming reference describes on page 176 that "Table 21 lists all the user option bytes managed through the embedded Flash memory registers, as well as their default values..."

Table 21 describes only 8 32-bit words, which would seem to leave 2048 - 32 = 2016 bytes of memory remaining. I want to use this option byte space in flash to store a few data bytes my application needs in non-volatile memory.

How can I write to the area of these flash option bytes not reserved for the other functions described in Table 21 of the programming reference manual?

Thanks!

-Brian

[TDK]

You can't access them. I don't know why they say 2 kB are available if you can only access a subset. Presumably a disconnect between what is technically on the hardware and what is actually usable.

If you want to store persistent data, you'll need to use a page of flash or external EEPROM, FRAM or similar.

[Andreas Bolsch]

You can't. The remaining space is probably reserved for ST's purposes like calibration data, disabling certain features etc. Most certainly this space is directly mapped into general address space during production but direct access disabled prior to shipment. In particular the H750 is the same die as H743, so e.g. there must be a way to disable the crypt functions permanently. Via some hidden option bytes would be a rather feasible option ...