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STM32F070CBT6 USB Bootloader does not work


Hello. I am using a STM32F070CBT6 uC with the FG-code $36, meaning it should contain bootloader version V10.3.

The chip marking is:




AA067 019C

TWN AA 016

ST (e3) 2


By breaking when the bootloader is running, the HSITRIM register reads as 0 which is compatible with the bug mentioned in AN2606 section 10.3 regarding bootloader version 10.2, but that should have been updated/corrected to 0x16 in bootloader version V10.3 (?)

Registers read while in bootloader (all RCC registers not listed was set to 0)

RCC:CR = 0x30b4403

RCC:CFGR = 0x19000a

RCC:AHBENR = 0x60014


RCC:APB1ENR = 0x10800100

RCC:BDCR = 0x18

RCC:CSR = 0x1c800000

RCC:CFGR2 = 0x2

RCC:CFGR3 = 0x80

RCC:CR2 = 0x6b80

Bootloader id: 0xA3 (read from address 0x1FFFF6A6)

When accessing the bootloader over USART we get the following information.

stm32flash 0.5

Interface serial_posix: 57600 8E1

Version     : 0x31

Option 1    : 0x00

Option 2    : 0x00

Device ID   : 0x0448 (STM32F070xB/F071xx/F72xx)

- RAM       : 16KiB (6144b reserved by bootloader)

- Flash     : 128KiB (size first sector: 2x2048)

- Option RAM : 16b

- System RAM : 12KiB

We have a 16,0000MHz crystal connected to pin 5 and 6. (Nothing connected to pin 3 and 4, these are floating)

When we flash our own firmware (via USART) the USB port works flawlessly. But when starting the bootloader to be able to flash via USB, it simply doesn't work - we believe due to the fact that HSITRIM=0.

Do we have the correct boot loader version, and if so - why does it not work when using it?

Please, greatful for any help we can get on this issue.

Best regards /Bjorn