Bootloader issue 'F469 - cannot connect via UART after disabling Readout Protection

[ChrisJC]

Dear All,

 I am having difficulty with the Bootloader on an STM32469.

It is on a custom PCB (which works fine in all other respects), and I can use the SWD interface via J-Link perfectly OK (with both STM32CubeIDE and STM32CubeProgrammer).

My starting point is a board where the Readout Protection was set to Level 1. Note that this is true for all hardware I have access to, so I cannot try with a board that has never had Readout Protection applied.

I can reset the Readout Protection to Level 0 (0xAA) via J-Link. This erases Flash (expected behaviour).

I can check the FLASH peripheral registers via STM32CubeProg, and they all look OK.

I would now expect to be able to connect via UART with STM32CubeProgrammer.

However, when I reset my board with BOOT0 set high, and attempt to connect via UART, I get this:

I also get four popup error boxes:

1. Initialising the Option Bytes failed

2. Uploading Option Bytes bank 0 failed

3. READ command not acknowledged at address: 0x1fffc000

4. READ command not acknowledged at address: 0x1fffx008

You can see from the above dump that the Bootloader is operational and connected, but is not responding correctly.

I have verified this process on a NUCLEO-F401RE board to check my expectations are correct, and everything works as expected.

Please help.

Thanks,

Chris.

[Imen.D]

Hello @ChrisJC 

Check your boot mode configuration and boot pin connection following the AN4488 Application note, in section "Boot mode selection" and "Boot pin connection". 

[ChrisJC]

Hi Imen,

 Thank you for your reply.

As far as I know, I have configured boot mode selection correctly:

I have grounded BOOT1:

BOOT0 is connected to an external interface:

And to enter the Bootloader, I simply apply 3.3V to BOOT0 and reset the target.

I know it must be in Bootloader mode because you can see it correctly in the STM32CubeProg trace above as Chip ID: 0x434 which I believe has been read from the target?

My theory is that the Bootloader incorrectly believes the Readout Protection to be active?

What do you think?

Thank you.

Chris. 

[ChrisJC]

OK, so I just tried it on a brand new PCB, brand new STM32. Never been programmed, so factory fresh:

Exactly the same problem - the bootloader is rejecting the GetID with a NACK...

Chris.

[ChrisJC]

Replying to my own topic!

I think I know what is going on here:

I analysed the serial comms, and there was an additional 0x7f at the start. So the sequence was

PC->Target = 0x7f

Target->PC = 0x79 ACK

PC->Target = 0x7f - THIS IS SPURIOUS

Target->PC = 0x1f NACK

After this, it all falls over. There are also some badly framed bytes being sent by the PC.

I checked with an Nucleo-F429 that I had lying around, which worked correctly.

I checked logic levels and signal integrity with the oscilloscope, everything looked perfect.

Eventually I switched the USB-RS232 converter from an MCP2200 (Microchip) to a CP2101 (SiLabs), and everything seems to be working (as far as I have tested it - it's getting late!). I can connect, maintain a connection, perform a mass erase and download an image.

So it seems there's some weird incompatibility between Windows 11, the MCP2200 driver and STM32CubeProg.

Note I have been using the MCP2200 for normal serial comms with no issues at all, so it's probably an STM32CubeProg / Java bug.

I'll test the Readout Protection in due course.

Chris.