You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
150 lines
6.9 KiB
Plaintext
150 lines
6.9 KiB
Plaintext
Version 2009-08-22
|
|
|
|
==========================
|
|
WHY DO WE NEED THESE IDs?
|
|
==========================
|
|
|
|
USB is more than a low level protocol for data transport. It also defines a
|
|
common set of requests which must be understood by all devices. And as part
|
|
of these common requests, the specification defines data structures, the
|
|
USB Descriptors, which are used to describe the properties of the device.
|
|
|
|
From the perspective of an operating system, it is therefore possible to find
|
|
out basic properties of a device (such as e.g. the manufacturer and the name
|
|
of the device) without a device-specific driver. This is essential because
|
|
the operating system can choose a driver to load based on this information
|
|
(Plug-And-Play).
|
|
|
|
Among the most important properties in the Device Descriptor are the USB
|
|
Vendor- and Product-ID. Both are 16 bit integers. The most simple form of
|
|
driver matching is based on these IDs. The driver announces the Vendor- and
|
|
Product-IDs of the devices it can handle and the operating system loads the
|
|
appropriate driver when the device is connected.
|
|
|
|
It is obvious that this technique only works if the pair Vendor- plus
|
|
Product-ID is unique: Only devices which require the same driver can have the
|
|
same pair of IDs.
|
|
|
|
|
|
=====================================================
|
|
HOW DOES THE USB STANDARD ENSURE THAT IDs ARE UNIQUE?
|
|
=====================================================
|
|
|
|
Since it is so important that USB IDs are unique, the USB Implementers Forum,
|
|
Inc. (usb.org) needs a way to enforce this legally. It is not forbidden by
|
|
law to build a device and assign it any random numbers as IDs. Usb.org
|
|
therefore needs an agreement to regulate the use of USB IDs. The agreement
|
|
binds only parties who agreed to it, of course. Everybody else is free to use
|
|
any numbers for their IDs.
|
|
|
|
So how can usb.org ensure that every manufacturer of USB devices enters into
|
|
an agreement with them? They do it via trademark licensing. Usb.org has
|
|
registered the trademark "USB", all associated logos and related terms. If
|
|
you want to put an USB logo on your product or claim that it is USB
|
|
compliant, you must license these trademarks from usb.org. And this is where
|
|
you enter into an agreement. See the "USB-IF Trademark License Agreement and
|
|
Usage Guidelines for the USB-IF Logo" at
|
|
http://www.usb.org/developers/logo_license/.
|
|
|
|
Licensing the USB trademarks requires that you buy a USB Vendor-ID from
|
|
usb.org (one-time fee of ca. 2,000 USD), that you become a member of usb.org
|
|
(yearly fee of ca. 4,000 USD) and that you meet all the technical
|
|
specifications from the USB spec.
|
|
|
|
This means that most hobbyists and small companies will never be able to
|
|
become USB compliant, just because membership is so expensive. And you can't
|
|
be compliant with a driver based on V-USB anyway, because the AVR's port pins
|
|
don't meet the electrical specifications for USB. So, in principle, all
|
|
hobbyists and small companies are free to choose any random numbers for their
|
|
IDs. They have nothing to lose...
|
|
|
|
There is one exception worth noting, though: If you use a sub-component which
|
|
implements USB, the vendor of the sub-components may guarantee USB
|
|
compliance. This might apply to some or all of FTDI's solutions.
|
|
|
|
|
|
=======================================================================
|
|
WHY SHOULD YOU OBTAIN USB IDs EVEN IF YOU DON'T LICENSE USB TRADEMARKS?
|
|
=======================================================================
|
|
|
|
You have learned in the previous section that you are free to choose any
|
|
numbers for your IDs anyway. So why not do exactly this? There is still the
|
|
technical issue. If you choose IDs which are already in use by somebody else,
|
|
operating systems will load the wrong drivers and your device won't work.
|
|
Even if you choose IDs which are not currently in use, they may be in use in
|
|
the next version of the operating system or even after an automatic update.
|
|
|
|
So what you need is a pair of Vendor- and Product-IDs for which you have the
|
|
guarantee that no USB compliant product uses them. This implies that no
|
|
operating system will ever ship with drivers responsible for these IDs.
|
|
|
|
|
|
==============================================
|
|
HOW DOES OBJECTIVE DEVELOPMENT HANDLE USB IDs?
|
|
==============================================
|
|
|
|
Objective Development gives away pairs of USB-IDs with their V-USB licenses.
|
|
In order to ensure that these IDs are unique, Objective Development has an
|
|
agreement with the company/person who has bought the USB Vendor-ID from
|
|
usb.org. This agreement ensures that a range of USB Product-IDs is reserved
|
|
for assignment by Objective Development and that the owner of the Vendor-ID
|
|
won't give it to anybody else.
|
|
|
|
This means that you have to trust three parties to ensure uniqueness of
|
|
your IDs:
|
|
|
|
- Objective Development, that they don't give the same PID to more than
|
|
one person.
|
|
- The owner of the Vendor-ID that they don't assign PIDs from the range
|
|
assigned to Objective Development to anybody else.
|
|
- Usb.org that they don't assign the same Vendor-ID a second time.
|
|
|
|
|
|
==================================
|
|
WHO IS THE OWNER OF THE VENDOR-ID?
|
|
==================================
|
|
|
|
Objective Development has obtained ranges of USB Product-IDs under two
|
|
Vendor-IDs: Under Vendor-ID 5824 from Wouter van Ooijen (Van Ooijen
|
|
Technische Informatica, www.voti.nl) and under Vendor-ID 8352 from Jason
|
|
Kotzin (Clay Logic, www.claylogic.com). Both VID owners have received their
|
|
Vendor-ID directly from usb.org.
|
|
|
|
|
|
=========================================================================
|
|
CAN I USE USB-IDs FROM OBJECTIVE DEVELOPMENT WITH OTHER DRIVERS/HARDWARE?
|
|
=========================================================================
|
|
|
|
The short answer is: Yes. All you get is a guarantee that the IDs are never
|
|
assigned to anybody else. What more do you need?
|
|
|
|
|
|
============================
|
|
WHAT ABOUT SHARED ID PAIRS?
|
|
============================
|
|
|
|
Objective Development has reserved some PID/VID pairs for shared use. You
|
|
have no guarantee of uniqueness for them, except that no USB compliant device
|
|
uses them. In order to avoid technical problems, we must ensure that all
|
|
devices with the same pair of IDs use the same driver on kernel level. For
|
|
details, see the file USB-IDs-for-free.txt.
|
|
|
|
|
|
======================================================
|
|
I HAVE HEARD THAT SUB-LICENSING OF USB-IDs IS ILLEGAL?
|
|
======================================================
|
|
|
|
A 16 bit integer number cannot be protected by copyright laws. It is not
|
|
sufficiently complex. And since none of the parties involved entered into the
|
|
USB-IF Trademark License Agreement, we are not bound by this agreement. So
|
|
there is no reason why it should be illegal to sub-license USB-IDs.
|
|
|
|
|
|
=============================================
|
|
WHO IS LIABLE IF THERE ARE INCOMPATIBILITIES?
|
|
=============================================
|
|
|
|
Objective Development disclaims all liabilities which might arise from the
|
|
assignment of IDs. If you guarantee product features to your customers
|
|
without proper disclaimer, YOU are liable for that.
|