Re: [libusb] using libusb with multiple endpoints

[Tim R. <ti...@pr...>]

On Jul 4, 2019, at 8:28 AM, ALAN BALL via libusb-devel <lib...@li...> wrote:
> 
> I've been able to check that the VCOM interface works OK using tera term. I've tried to modify my libusb based PC application (by changing the interface number and endpoints) to communicate with my embedded device but I get the following errors:
> 
> Device Opened
> libusb: error [parse_endpoint] invalid extra ep desc len (0)
> libusb: error [raw_desc_to_config] parse_configuration failed with error -1
> libusb: warning [windows_assign_endpoints] could not read config descriptor: error -1

That looks like a descriptor problem.  Have you used usbview or usbtreeview to make sure your descriptors are entirely correct?

> Is this a limitation of libusb? Is the libusb library unable to use multiple endpoints? 

Multiple endpoints are not a problem, but you have a somewhat interesting situation.  Ordinarily, when you’re using multiple interfaces, you’d have libusb claim the composite device.  Then you can select whatever interfaces you need.  In your case, you have to let the operating system assign usbccgp to the composite devices so it creates subdevices for each interface.  That means, among other things, you will have two separate driver instances for your two libusb devices.  To be honest, I’m not sure how libusb handle that situation.

How are you claiming the device and the interfaces?
— 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.