STM32 USB Host CDC class: USBH_FindInterface issue

[DDeba.1]

Hi, 

I am using STM32G0B1CBTX and used the STM32CubeMX to configure USB host with CDC class. When connecting a CDC device, I noticed that it passes the enumeration and configuration but fails to find the interface used. More specifically, it fails the function

interface = USBH_FindInterface(phost, COMMUNICATION_INTERFACE_CLASS_CODE, ABSTRACT_CONTROL_MODEL, COMMON_AT_COMMAND);

at line 158 of the usbh_cdc.c file. Upon deeper inspection, I noticed that the protocol value passed to this function using the macro COMMON_AT_COMMAND is set to 1 while the two interface descriptors I receive from the device both have their interface protocol set to 0. If I manually edit this and use the  NO_CLASS_SPECIFIC_PROTOCOL_CODE macro (value = 0), everything works correctly and I can send and receive data. This part of the library should be fixed and no user editing should be needed. So my question is, is their something wrong with the device's descriptors or can the first call to the USBH_FindInterface be set to have no specific protocol instead of using the COMMON_AT_COMMAND one?

[FBL]

Hi @DDeba.1 

Are you using a reference board or custom board? Would you attach the project to reproduce on my end?

[DDeba.1]

Hi @FBL,

Find attached what requested. Note that this is basically the CubeMX generated code where I only changed line 158 of the usbh_cdc.c file such that the last argument of the USBH_FindInterface is NO_CLASS_SPECIFIC_PROTOCOL_CODE. 

Thanks

[FBL · Accepted solution]

Hi @DDeba.1 

Thank you for reporting! Indeed, after sharing this with our experts, this could be customized since this middleware was intended to find interface only for COMMON_AT_COMMAND. However, the fix could take some time. 

[DDeba.1]

Hi @FBL,

Thanks for clarifying. In this regards, is there a way I can make this change without having the STM32CubeMX overwriting my change every time I regenerate my code?

[FBL]

Hi @DDeba.1 

Unfortunately, no possible workaround in such case, since USBH_FindInterface() is copied from MW layer directly. You need to overwrite it every time you regenerate the code.