On 'F407, RTC Backup Registers cannot be read using SWD if RDP Level 1 is set

[waclawek.jan]

In STM32F407 locked to RDP Level 1, with a battery on VBAT, I keep some (not critical) data in the RTC Backup Registers.

In an attempt to investigate an incident, I tried to read out content of these registers using SWD. While I was able to read RTC registers correctly, all RTC Backup Registers read as 0 (which, according to the behaviour of program, was not true). After changing RDP to Level 0, I was able to read the correct, unperturbed content of Backup Registers.

I could not find this behaviour to be documented in RM0090.

Can ST please comment?

Thanks,

JW

[Amel NASRI]

Hi @Community member​ ,

I need to check this & I'll come back to you.

-Amel

[waclawek.jan]

Thanks, Amel.

Jan

[waclawek.jan]

Incidentally, I've looked at RM0091 (the 'F0 RM), and there Memory protection - Read protection subchapter states:

Level 1: read protection

Debug, boot RAM and boot loader modes: In debug mode (with SWD) or when code

is running from boot RAM or boot loader, the main Flash memory and the backup

registers (RTC_BKPxR in the RTC) are totally inaccessible.

Can please ST be consistent in describing the same feature in *all* RMs.

JW

@Amel NASRI​