Boot from USB OTG pins on STM32MP131

[MaxMKA]

Hi everyone,

we are in the middle of bringing up a custom board using the STM32MP131. Booting from an SD card already works. However, we would like to use the STM32CubeProgrammer to directly connect the board via USB. For this, the OTG USB pins OTG_HS_DP and OTG_HS_DM are wired to a USB-A socket. The socket is then connected to a PC using a USB-A to USB-A cable. In serial boot mode, the LED on BOOTFAILN blinks at 5Hz, but the device does not show up on the computer.

I assume that this is a hardware issue since USB boot should work before any software is loaded on the device. USB boot works with the STM32MP135-DK, so it should not be a driver issue either. On our board, OTG_HS_ID (PA10) is left floating. This pin has an internal pull-up, which should signal device mode by default. OTG_HS_VBUS (PI7) is also left floating. On the DK-board it is connected to the LCD, so it should also be optional. Power is supplied seperately via the STPMIC1. The MPU and USB port are wired like this:

I am unsure what could be preventing the device from being recognized by the PC. Are there any reference schematics apart from the discovery board? Am I overlooking something?

Best regards

Max

[MaxMKA · Accepted solution]

Solved it. VDD3V3_USB was not powered. The ID and VBUS pins are indeed optional.