Class descriptor question

[ChicagoMike]

Hello,

I'm having a bit of a problem wrapping my head around the following: The class descriptors for HID and DFU device classes are both of type 0x21. If a USB device exposes both DFU and HID interfaces, and subsequently receives from its host a GET_DESCRIPTOR request with wValue set to 0x2100, how is the device to know whether to send its HID descriptor or its DFU descriptor?

Thanks for your help,

Mike

[JohnHyde]

With a CLASS Get_Descriptor Request wIndexLow = Interface Number.  Your Composite Device (HID + DFU) will define 2 interfaces, 0 and 1, within the Configuration Descriptor.  So check wIndexLow and return the correct one.

Regards,  John

[ChicagoMike]

Awesome!

Thanks so much for your help.

Mike