Re: [libusb] Correct use of libusb with composite device

[RisingEdgeIndustries <su...@ri...>]

Do you have to pass a GUID value to get WINUSB to be associated with a
composite device using MS OS 2.0 descriptors?  I thought this unique
identifier was optional in case you wanted it in the registry to find your
device?





On Tue, Jul 18, 2023 at 1:16 AM Tim Roberts <ti...@pr...> wrote:

> On 7/17/23 7:01 PM, RisingEdgeIndustries wrote:
>
>
> *Question 1:*
> It seems the key to MS OS 2.0 Descriptors is to set the bcdUSB field to
> USB version 2.1 with a hex value of 0x0210.  This is pretty
> straightforward, but as I"m using a USB 2.0 full speed device right now I
> want to make sure there isn't something I'm missing that would render this
> MS OS 2.0 descriptor approach incompatible due to a USB 2.0 full speed
> device setting its bcdUSB version to 2.1.  Is this bcdUSB field only to
> tell windows which MS OS descriptor version is supported or does it play a
> role in determining other operational metrics?  I'm a little unsure because
> the field defines *"USB Specification number which the device complies
> to"*.  This leads me to believe I can't just plug in 0x0210 to get MS OS
> 2.0 descriptors - there are other thing associated with using this value
> over 0x0200 which I'm using now for MS OS v1.0 descriptors
>
> There should be no incompatible changes -- there almost never are when the
> version changes.  Microsoft uses the BOS to find out whether the OS 2.0
> descriptors are present, and the BOS is only supported with USB 2.1.
>
>
> *Question 2:*
> I read that WINUSB (I guess this is more a WINUSB thing than libusb1.0)
> doesn't support access from multiple applications.
>
> Yes, although that's not the only driver that has that limitation.
> Sharing a USB device between multiple applications is very tricky.
>
>
> My goal is to have a logically asynchronous feel to the HID interface by
> allowing a thread to monitor it and when data is present grab it and hand
> it off to the main application thread.
>
> That's fine; it's kind of how the USB HID drivers work.
>
>
> The reason I ask Question #2 is because I tried this with libusb1.0 and
> didn't know how to handle the two interfaces.  If I"m correct in my
> understanding that this approach will work, what is the correct way to get
> a hold of these two interfaces in the same application?  Do I make two
> device handles and have one device handle the HID interface and the other
> device handle the bulk interface.
>
> Yep, that's how you do it.
> --
>
> Tim Roberts, ti...@pr...
> Providenza & Boekelheide, Inc.
>
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