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

[Robert R. <R.R...@Qu...>]

Hi Matthias,

At 06:08 PM 9/22/2021 +0200, Matthias Bolte wrote:
>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.

I doubt I will be doing this for more than 5 more years so I don't see any
reason why the devices I develop between now and then will not be
compatible.  I guess I am not sure why the would not be? In the code
I posted, I save the handle, VID, PID and SN to a structure and I pass
a pointer to that structure back to the other code to determine what to
do with that PID.  Thanks for your insights.  I am going to try the newest
version of the lib to see if it makes any difference.


>Regards
>Matthias

-Bob
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Robert Ritchey
Quest Engineering & Development, Inc.
Suite B-8
6125 South Ash Avenue
Tempe, AZ 85283
Tel: (480) 460-2652
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