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STM32F303 internal bootloader does not work - pt. II

Question asked by Davide Rizzi on Oct 6, 2017

Hello everybody,

  I am still having problems with the STM32F303 bootloader.



  • STM32F303CC
  • External 24MHz CMOS oscillator
  • 1.5kohm pullup on USB_DP
  • USB working perfectly (in the application: no issues whatsoever, tens of boards deployed)
  • BOOT0 pin pulled up


On 3 out of 6 boards, the USB does never get enumerated. The boards keep resetting randomly - the reset is software.

On 2/6 boards everything works reliably, while the other board works "sometimes".


The HSE ready bit in RCC_CR is 1, and it seems to stay that way (the HSE bypass bit in RCC_CR is 0 - can it be a problem with an external oscillator?).


I have no clues. What I have discovered is that only at times the FW tries to configure the USB - at times it skips it. At times the FW ends in a loop where it keeps resetting the watch dog, at times it ends in a loop where it reads pin status from GPIOA and GPIOD. Most of the times it simply reset.

I cannot find out what causes this reset - all the vectors bring to 0x1fffed10. And, by the way, stepping through asm code can be very tiring. ;-)