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