STM32H7S78-DK - Using USB-C for DFU-Bootloader and USB-HS host

[rk_iot]

Hello,

on the STM32H7S78-DK board only USB2 (=USB-FS) can be used to connect the board to a PC and flash the firmware via USB-DFU because only PM11 and PM12 are supported by the internal USB-DFU bootloader.

Is there a way to modify the board or to create a custom design with only one USB-C connector with is both connected to USB-FS and USB-HS pins, which can be connected to a PC at startup and shows up as an DFU device when the DFU bootloader is activated at startup but later on acts as an USB-HS host when the application is started?

One idea would be to simply connect both PM2/PM3 of the USB-HS phy and PM11/PM12 of the USB-FS phy together and only enable the PHY needed - either for DFU-bootloader or for the USB-HS host, but it is not clear if this is allowed and will be working.

Background would be to only need one USB-C connector which normally acts as an USB-HS host but could also be use to flash the firmware via an PC by using the DFU bootloader.

Thanks for you help

best regards

rk_iot

[FBL]

Hi @rk_iot 

PM2/PM3 could be connected as dead battery pins to CC lines not to data lines ! 

Here some suggestions :

1. You need to ensure that the switch/multiplexer you use can handle the USB data rates without significant signal degradation.
2. Your software should handle the enumeration and initialization of the USB peripherals correctly when switching.
3. Ensure that the switching does not violate USB specifications and that the device remains compliant.