Re: [Libusb-devel] USB VID/PID for open source projects

[Segher B. <se...@ke...>]

>     Segher> There are also many clones of the jtagkey that use the same
>     Segher> vid/pid.
>
>     Segher> This device is also a good example of why it is *bad* to use
> the
>     Segher> same vid/pid on multiple devices: all of them seem to be
>     Segher> different in the sense of the TRST and SRST outputs (polarity,
>     Segher> push/pull vs. open drain).  This makes it impossible to use a
>     Segher> jtagkey (clone; it might just be the clones that differ!)
>     Segher> without looking at the device strings first, to properly
>     Segher> identify the device.
>
> What is bad to require to read the device string?

Then vid/pid alone isn't enough to identify the device; which is the
purpose of vid/pid.

The purpose of the device string is not to identify a device for
programmatic purposes (instead, it is for human consumption only);
using a single datum for two conflicting purposes is not a good thing.

There is no mechanism in place to prevent allocating the same device
string to two different devices, not even when those devices share
the same vid/pid.

In practice, using the device string to distinguish between _a few_
devices that share a vid/pid usually works fine of course.


Segher