git.zerfleddert.de Git - fnordlicht-mini/blob - firmware/fnordlicht-controller/usbdrv/USB-ID-FAQ.txt

   1 Version 2009-08-22
   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 (Clay Logic, www.claylogic.com). Both VID owners have received their
 111 Vendor-ID 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.