STM32H7S78-DK: USBX standalone (CDC ACM + PIMA) works in FS; fails in HS
in HS, HAL_PCD_Init fails with timeout in USB_CoreReset
Hello everyone,
I am working with an STM32H7S78-DK and I’m trying to use USBX in standalone mode for a composite USB device (CDC ACM + PIMA) over USB_HS at 480 Mbit/s.
At the moment, I have only implemented the CDC ACM class. PIMA will be added later.
Situation:
- If I configure USB as Full Speed, the peripheral initializes correctly.
- If I switch to High Speed, initialization fails at:
MX_USBX_Init() -> MX_USBX_Device_Init() -> MX_USB_OTG_HS_PCD_Init() -> HAL_PCD_Init(&hpcd_USB_OTG_HS)
The error occurs at:
if (USB_CoreInit(hpcd->Instance, hpcd->Init) != HAL_OK) { ... }
Because inside USB_CoreInit, in USB_CoreReset, a HAL_TIMEOUT is returned while waiting for the CSRST bit in GRSTCTL to clear:
- Core Soft Reset (CSRST) is written
- The bit never clears and eventually times out
Technical summary:
- FS works, HS does not
- The timeout occurs right after PHY selection and USB core reset
- The issue seems related to clock/PHY/HS configuration
- I have also tried configuring the HS peripheral but forcing Full Speed operation (12 Mbit/s), and it still does not work
Has anyone successfully configured USB_HS with USBX standalone on this family and can confirm which settings are required to avoid this timeout?
In particular:
- Is an external ULPI PHY mandatory to reach 480 Mbit/s on this board? From what I understand based on the microcontroller datasheet, it should not be strictly necessary, but I would appreciate confirmation.
- Which exact clocks must be enabled for the HS core to complete CSRST?
- Are there any critical settings in CubeMX (PHY selection, VBUS sensing, power/clock domains) that commonly cause CSRST to get stuck?
- Does CDC ACM + PIMA in standalone mode require any special HS initialization sequence?
I’ve attached a ZIP file with the full project for reference.
Thanks in advance!
