SWD connection no longer working

[RHaag.1]

Hello,

On a STM32L4 design, we no longer have an SWD connection to the processor: using STM32CubeProgrammer reports

ST-LINK SN : 39FF6A064243383912381057

ST-LINK FW : V2J36S7

Voltage : 3.26V

SWD freq : 4000 KHz

Connect mode: Normal

Reset mode : Software reset

Device ID : 0x461

UPLOADING OPTION BYTES DATA ...

Bank : 0x00

Address : 0x40022020

Size : 20 Bytes

Bank : 0x01

Address : 0x40022044

Size : 16 Bytes

UPLOADING ...

Size : 1024 Bytes

Address : 0x8000000

Read progress:

Error: Data read failed

SWD works fine in the design in general, also also ran on this particular device. An idea what is missing?

Or to put it the other way round: what do we need for a running SWD? Supply, connection to the SWD pins of course, but what further? IMHO we don't need running CPU core or clocking on it for example....

Thank you

Ralph

[Houda GHABRI]

Hi @RHaag.1​ ,

In this case the value of RDP OB can be any value other than 0xAA and 0xCC (so it can be 0xFF).

Houda

[RHaag.1]

Hi Houda,

hm, is there an error in the ref manual with level 0 / 1 here?

Anyhow, I know programming any value other than 0xAA and 0xCC will lead to level 1, but I'm sure ST knows what value I should read back in assumed case with mismatch in comparison of stored option byte! Is it 0xFF or not?

Regards

Ralph

[Houda GHABRI]

Hi @RHaag.1​ ,

You can refer to table 14 in RM0351 3.5 Flash memory protection :

Houda

[RHaag.1]

Hi Houda,

it's a valuable discussion, but I still don't know the RDP value when the comparission doesn't match. I know it can be "my" 0xFF, but I'm quite sure ST implemented a certain value in this case not a "could be anything except..." :)

Regards

Ralph