STM32H7 USB DEVICE CDC PROBLEM

[PanosGial]

I am trying to use STM32H747IGT6 as a USB device. I want to sent data using CDC. Below you can find my configuration and code. The MX_USB_DEVICE_Init() is successful. Although when I call the CDC_Transmit_FS, it never returns USB_OK and I wasn't able to find the USB device through my laptop. 
The only thing I found is that after the initialization done by the ST Generated code, the struct with the device configuration is still NULL and it seems that nothing is actually initialised and I assume that this is a problem. Although the initialization function returns USB_OK. 
Does anyone have any ideas about this problem?
If you need further information about the project please let me know.

[STea]

Hello @PanosGial ,

can you please send the generated MX_USB_DEVICE_Init() function and give more details about the CubeMX version you are using to further investigate your issue ?

BR

[PanosGial]

I am using the version 1.14.0 of STM32CubeIDE
Here is the MX_USB_DEVICE_init()
I  tried moving HAL_PWREx_EnableUSBVoltageDetector() above the other functions(inside USER CODE BEGIN USB_DEVICE_INIT_PreTreatment) but nothing changes.

Thank you in advance

[Sebastiaan]

Are you using a nucleo board or your own design?

If the device is not even recognized by your PC, that could indicate pinout issues. The device should put a high signal on D+ so that the laptop can detect a new USB device.

If that's not happening, maybe an external pull-up is required on D+ (could be that your STM32 does not automatically control D+, that info is in the datasheet).

[Sebastiaan]

Your code uses "HAL_PWREx_EnableUSBVoltageDetector()" but VBUS sensing is disabled in your cubemx configuration? At least, I suppose that's what "HAL_PWREx_EnableUSBVoltageDetector" is for but I'm not sure. It's worth to verify that too.. The easiest (if you don't need it) is to keep vbus sensing disabled.

[PanosGial]

This is a custom design. The pinout is ok and the external pull up is applied but I cannot detect the USB device from my laptop

[Pavel A.]

Use a decent Linux machine; enable kernel trace (dmesg). Observe the dmesg after plug in the device (compare with a good CDC device like a USB to serial adapter). If still there's absolutely nothing in dmesg, there is one of problems mentioned by @Sebastiaan. Dual-core STM32H7 are complicated, you may want to start from a simpler single-core MCU.

[Sebastiaan]

Actually, in the reference manual (rm0399), it's mentioned that DP (and DM) have integrated pull-ups and pull-downs. So in that case, you don't need, and don't even want external pull-ups.

We had the same issue on an STM32F4, where pull-ups were integrated, but also added externally. As a consequence, your laptop immediately detects the pull-up and tries to communicate, but the USB peripheral is not yet started, and hence the initialization (negotiation) procedure fails, and on windows this pops up as an error like "could not read device descriptor".

In windows device manager, you can disable and re-enable the device to launch a new negotiation when the USB stack is running. On linux, similar information can indeed be retrieved via dmesg log, as @Pavel A. points out, and there certainly must be a way to re-trigger the USB detection too.