0,0 → 1,149 |
Version 2012-07-09 |
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WHY DO WE NEED THESE IDs? |
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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. |
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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). |
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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. |
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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. |
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HOW DOES THE USB STANDARD ENSURE THAT IDs ARE UNIQUE? |
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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. |
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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/. |
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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. |
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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... |
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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. |
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WHY SHOULD YOU OBTAIN USB IDs EVEN IF YOU DON'T LICENSE USB TRADEMARKS? |
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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. |
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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. |
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HOW DOES OBJECTIVE DEVELOPMENT HANDLE USB IDs? |
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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. |
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This means that you have to trust three parties to ensure uniqueness of |
your IDs: |
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- 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. |
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WHO IS THE OWNER OF THE VENDOR-ID? |
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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 (now flirc.tv, Inc.). Both VID owners have received their Vendor-ID |
directly from usb.org. |
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CAN I USE USB-IDs FROM OBJECTIVE DEVELOPMENT WITH OTHER DRIVERS/HARDWARE? |
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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? |
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WHAT ABOUT SHARED ID PAIRS? |
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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. |
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I HAVE HEARD THAT SUB-LICENSING OF USB-IDs IS ILLEGAL? |
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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. |
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WHO IS LIABLE IF THERE ARE INCOMPATIBILITIES? |
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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. |