Hi all,
I'm planning to use USB (DFU mode) for production programming of the STM32C071K8U6 — including the very first firmware upload. The board has no external crystal; I intend to rely solely on the internal RC oscillator.
A few questions:
1) Is USB DFU feasible on this specific part without an external crystal? I've read that not all STM32 variants support USB boot without an external crystal (due to clock accuracy requirements for USB). Can anyone confirm whether the STM32C071K8U6's internal oscillator is sufficiently accurate for this?
2) Are there any specific hardware or configuration requirements I should be aware of for first-time USB DFU programming on this part? As the moment I just have the two USB traces connected to the USB connector but no 5V (VBUS) connected anywhere to the micro. I also have a pushbutton on the BOOT0 pin.
3) What USB speed does the built-in bootloader use, and is it possible to force a lower speed? The reason I ask is that the USB D+/D− lines have relatively long stubs — because after programming, these traces are repurposed for other functionality and never for USB, so they branch out to various areas of the PCB. USB is used exclusively for programming, and I'd like to understand whether the stub lengths could be problematic and whether reducing the speed would help mitigate signal integrity issues.
Thank you in advance
