comparison: usbdrv/USB-ID-FAQ.txt
usbdrv/USB-ID-FAQ.txt
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| 1 Version 2012-07-09 | |
| 2 | |
| 3 ========================== | |
| 4 WHY DO WE NEED THESE IDs? | |
| 5 ========================== | |
| 6 | |
| 7 USB is more than a low level protocol for data transport. It also defines a | |
| 8 common set of requests which must be understood by all devices. And as part | |
| 9 of these common requests, the specification defines data structures, the | |
| 10 USB Descriptors, which are used to describe the properties of the device. | |
| 11 | |
| 12 From the perspective of an operating system, it is therefore possible to find | |
| 13 out basic properties of a device (such as e.g. the manufacturer and the name | |
| 14 of the device) without a device-specific driver. This is essential because | |
| 15 the operating system can choose a driver to load based on this information | |
| 16 (Plug-And-Play). | |
| 17 | |
| 18 Among the most important properties in the Device Descriptor are the USB | |
| 19 Vendor- and Product-ID. Both are 16 bit integers. The most simple form of | |
| 20 driver matching is based on these IDs. The driver announces the Vendor- and | |
| 21 Product-IDs of the devices it can handle and the operating system loads the | |
| 22 appropriate driver when the device is connected. | |
| 23 | |
| 24 It is obvious that this technique only works if the pair Vendor- plus | |
| 25 Product-ID is unique: Only devices which require the same driver can have the | |
| 26 same pair of IDs. | |
| 27 | |
| 28 | |
| 29 ===================================================== | |
| 30 HOW DOES THE USB STANDARD ENSURE THAT IDs ARE UNIQUE? | |
| 31 ===================================================== | |
| 32 | |
| 33 Since it is so important that USB IDs are unique, the USB Implementers Forum, | |
| 34 Inc. (usb.org) needs a way to enforce this legally. It is not forbidden by | |
| 35 law to build a device and assign it any random numbers as IDs. Usb.org | |
| 36 therefore needs an agreement to regulate the use of USB IDs. The agreement | |
| 37 binds only parties who agreed to it, of course. Everybody else is free to use | |
| 38 any numbers for their IDs. | |
| 39 | |
| 40 So how can usb.org ensure that every manufacturer of USB devices enters into | |
| 41 an agreement with them? They do it via trademark licensing. Usb.org has | |
| 42 registered the trademark "USB", all associated logos and related terms. If | |
| 43 you want to put an USB logo on your product or claim that it is USB | |
| 44 compliant, you must license these trademarks from usb.org. And this is where | |
| 45 you enter into an agreement. See the "USB-IF Trademark License Agreement and | |
| 46 Usage Guidelines for the USB-IF Logo" at | |
| 47 http://www.usb.org/developers/logo_license/. | |
| 48 | |
| 49 Licensing the USB trademarks requires that you buy a USB Vendor-ID from | |
| 50 usb.org (one-time fee of ca. 2,000 USD), that you become a member of usb.org | |
| 51 (yearly fee of ca. 4,000 USD) and that you meet all the technical | |
| 52 specifications from the USB spec. | |
| 53 | |
| 54 This means that most hobbyists and small companies will never be able to | |
| 55 become USB compliant, just because membership is so expensive. And you can't | |
| 56 be compliant with a driver based on V-USB anyway, because the AVR's port pins | |
| 57 don't meet the electrical specifications for USB. So, in principle, all | |
| 58 hobbyists and small companies are free to choose any random numbers for their | |
| 59 IDs. They have nothing to lose... | |
| 60 | |
| 61 There is one exception worth noting, though: If you use a sub-component which | |
| 62 implements USB, the vendor of the sub-components may guarantee USB | |
| 63 compliance. This might apply to some or all of FTDI's solutions. | |
| 64 | |
| 65 | |
| 66 ======================================================================= | |
| 67 WHY SHOULD YOU OBTAIN USB IDs EVEN IF YOU DON'T LICENSE USB TRADEMARKS? | |
| 68 ======================================================================= | |
| 69 | |
| 70 You have learned in the previous section that you are free to choose any | |
| 71 numbers for your IDs anyway. So why not do exactly this? There is still the | |
| 72 technical issue. If you choose IDs which are already in use by somebody else, | |
| 73 operating systems will load the wrong drivers and your device won't work. | |
| 74 Even if you choose IDs which are not currently in use, they may be in use in | |
| 75 the next version of the operating system or even after an automatic update. | |
| 76 | |
| 77 So what you need is a pair of Vendor- and Product-IDs for which you have the | |
| 78 guarantee that no USB compliant product uses them. This implies that no | |
| 79 operating system will ever ship with drivers responsible for these IDs. | |
| 80 | |
| 81 | |
| 82 ============================================== | |
| 83 HOW DOES OBJECTIVE DEVELOPMENT HANDLE USB IDs? | |
| 84 ============================================== | |
| 85 | |
| 86 Objective Development gives away pairs of USB-IDs with their V-USB licenses. | |
| 87 In order to ensure that these IDs are unique, Objective Development has an | |
| 88 agreement with the company/person who has bought the USB Vendor-ID from | |
| 89 usb.org. This agreement ensures that a range of USB Product-IDs is reserved | |
| 90 for assignment by Objective Development and that the owner of the Vendor-ID | |
| 91 won't give it to anybody else. | |
| 92 | |
| 93 This means that you have to trust three parties to ensure uniqueness of | |
| 94 your IDs: | |
| 95 | |
| 96 - Objective Development, that they don't give the same PID to more than | |
| 97 one person. | |
| 98 - The owner of the Vendor-ID that they don't assign PIDs from the range | |
| 99 assigned to Objective Development to anybody else. | |
| 100 - Usb.org that they don't assign the same Vendor-ID a second time. | |
| 101 | |
| 102 | |
| 103 ================================== | |
| 104 WHO IS THE OWNER OF THE VENDOR-ID? | |
| 105 ================================== | |
| 106 | |
| 107 Objective Development has obtained ranges of USB Product-IDs under two | |
| 108 Vendor-IDs: Under Vendor-ID 5824 from Wouter van Ooijen (Van Ooijen | |
| 109 Technische Informatica, www.voti.nl) and under Vendor-ID 8352 from Jason | |
| 110 Kotzin (now flirc.tv, Inc.). Both VID owners have received their Vendor-ID | |
| 111 directly from usb.org. | |
| 112 | |
| 113 | |
| 114 ========================================================================= | |
| 115 CAN I USE USB-IDs FROM OBJECTIVE DEVELOPMENT WITH OTHER DRIVERS/HARDWARE? | |
| 116 ========================================================================= | |
| 117 | |
| 118 The short answer is: Yes. All you get is a guarantee that the IDs are never | |
| 119 assigned to anybody else. What more do you need? | |
| 120 | |
| 121 | |
| 122 ============================ | |
| 123 WHAT ABOUT SHARED ID PAIRS? | |
| 124 ============================ | |
| 125 | |
| 126 Objective Development has reserved some PID/VID pairs for shared use. You | |
| 127 have no guarantee of uniqueness for them, except that no USB compliant device | |
| 128 uses them. In order to avoid technical problems, we must ensure that all | |
| 129 devices with the same pair of IDs use the same driver on kernel level. For | |
| 130 details, see the file USB-IDs-for-free.txt. | |
| 131 | |
| 132 | |
| 133 ====================================================== | |
| 134 I HAVE HEARD THAT SUB-LICENSING OF USB-IDs IS ILLEGAL? | |
| 135 ====================================================== | |
| 136 | |
| 137 A 16 bit integer number cannot be protected by copyright laws. It is not | |
| 138 sufficiently complex. And since none of the parties involved entered into the | |
| 139 USB-IF Trademark License Agreement, we are not bound by this agreement. So | |
| 140 there is no reason why it should be illegal to sub-license USB-IDs. | |
| 141 | |
| 142 | |
| 143 ============================================= | |
| 144 WHO IS LIABLE IF THERE ARE INCOMPATIBILITIES? | |
| 145 ============================================= | |
| 146 | |
| 147 Objective Development disclaims all liabilities which might arise from the | |
| 148 assignment of IDs. If you guarantee product features to your customers | |
| 149 without proper disclaimer, YOU are liable for that. |
