Re: [libusb] libusb_open returns -12 (LIBUSB_ERROR_NOT_SUPPORTED)

[Matthias B. <mat...@go...>]

Am Mi., 22. Sept. 2021 um 17:10 Uhr schrieb Robert Ritchey
<R.R...@qu...>:
>
> Hi Matthias,
> I wish to apologize for a misstatement I made.  See below
>
> At 11:18 AM 9/22/2021 +0200, Matthias Bolte wrote:
> >Am Mi., 22. Sept. 2021 um 03:38 Uhr schrieb Xiaofan Chen <xia...@gm...>:
> > >
> > > On Wed, Sep 22, 2021 at 7:37 AM Robert Ritchey
> > > <R.R...@qu...> wrote:
> > > >
> >
> >A few things to check:
> >
> >- Why are you only checking the vendor ID before opening the device?
> >You should check the product ID too to avoid trying to open the wrong
> >device.
>
> You are right, I do not check the Product ID before opening.
>
> I guess since this is my Vendor ID and I intend to use this for a number
> of devices (which device is checked elsewhere in the code) I did not see a
> reason to restrict the USB code to look for specific Product IDs.  My
> products range with an ID of 1 - 127 and the test fixtures are numbered
> from 128 - 255.  I guess I could check this range but why would another
> device have my Vendor ID and if it did, they could have a Product ID in
> the range of 1 -255 anyway.

Not everybody has their own VID these days. There were times where you
could buy a single PID without owning a full VID. That's why I'm
asking. Also are you sure that all your future USB devices with that
VID will be compatible with libusb? So there's a bit of future
proofing as well. I missed that you check the PID later on but only
after you already opened the device.

Regards
Matthias