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authorSam Bishop <sam@bishop.dhs.org>2006-08-28 18:42:10 -0400
committerGreg Kroah-Hartman <gregkh@suse.de>2006-09-27 14:58:48 -0400
commit341323269258ab8484077a9c70db804fbae6ae93 (patch)
tree10f2a93eee8f107ddb3e83acaa5778c01d24c0b0 /Documentation/DocBook/usb.tmpl
parent39c2f3ac04663bb2546a7058701a621e526eabb2 (diff)
USB: doc patch 1
Grammar, spelling, and stylistic edits. Signed-off-by: Sam Bishop <sam@bishop.dhs.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Diffstat (limited to 'Documentation/DocBook/usb.tmpl')
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1 files changed, 44 insertions, 54 deletions
diff --git a/Documentation/DocBook/usb.tmpl b/Documentation/DocBook/usb.tmpl
index 320af25de3a2..8a28f76b9359 100644
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@@ -43,59 +43,52 @@
43 43
44 <para>A Universal Serial Bus (USB) is used to connect a host, 44 <para>A Universal Serial Bus (USB) is used to connect a host,
45 such as a PC or workstation, to a number of peripheral 45 such as a PC or workstation, to a number of peripheral
46 devices. USB uses a tree structure, with the host at the 46 devices. USB uses a tree structure, with the host as the
47 root (the system's master), hubs as interior nodes, and 47 root (the system's master), hubs as interior nodes, and
48 peripheral devices as leaves (and slaves). 48 peripherals as leaves (and slaves).
49 Modern PCs support several such trees of USB devices, usually 49 Modern PCs support several such trees of USB devices, usually
50 one USB 2.0 tree (480 Mbit/sec each) with 50 one USB 2.0 tree (480 Mbit/sec each) with
51 a few USB 1.1 trees (12 Mbit/sec each) that are used when you 51 a few USB 1.1 trees (12 Mbit/sec each) that are used when you
52 connect a USB 1.1 device directly to the machine's "root hub". 52 connect a USB 1.1 device directly to the machine's "root hub".
53 </para> 53 </para>
54 54
55 <para>That master/slave asymmetry was designed in part for 55 <para>That master/slave asymmetry was designed-in for a number of
56 ease of use. It is not physically possible to assemble 56 reasons, one being ease of use. It is not physically possible to
57 (legal) USB cables incorrectly: all upstream "to-the-host" 57 assemble (legal) USB cables incorrectly: all upstream "to the host"
58 connectors are the rectangular type, matching the sockets on 58 connectors are the rectangular type (matching the sockets on
59 root hubs, and the downstream type are the squarish type 59 root hubs), and all downstream connectors are the squarish type
60 (or they are built in to the peripheral). 60 (or they are built into the peripheral).
61 Software doesn't need to deal with distributed autoconfiguration 61 Also, the host software doesn't need to deal with distributed
62 since the pre-designated master node manages all that. 62 auto-configuration since the pre-designated master node manages all that.
63 At the electrical level, bus protocol overhead is reduced by 63 And finally, at the electrical level, bus protocol overhead is reduced by
64 eliminating arbitration and moving scheduling into host software. 64 eliminating arbitration and moving scheduling into the host software.
65 </para> 65 </para>
66 66
67 <para>USB 1.0 was announced in January 1996, and was revised 67 <para>USB 1.0 was announced in January 1996 and was revised
68 as USB 1.1 (with improvements in hub specification and 68 as USB 1.1 (with improvements in hub specification and
69 support for interrupt-out transfers) in September 1998. 69 support for interrupt-out transfers) in September 1998.
70 USB 2.0 was released in April 2000, including high speed 70 USB 2.0 was released in April 2000, adding high-speed
71 transfers and transaction translating hubs (used for USB 1.1 71 transfers and transaction-translating hubs (used for USB 1.1
72 and 1.0 backward compatibility). 72 and 1.0 backward compatibility).
73 </para> 73 </para>
74 74
75 <para>USB support was added to Linux early in the 2.2 kernel series 75 <para>Kernel developers added USB support to Linux early in the 2.2 kernel
76 shortly before the 2.3 development forked off. Updates 76 series, shortly before 2.3 development forked. Updates from 2.3 were
77 from 2.3 were regularly folded back into 2.2 releases, bringing 77 regularly folded back into 2.2 releases, which improved reliability and
78 new features such as <filename>/sbin/hotplug</filename> support, 78 brought <filename>/sbin/hotplug</filename> support as well more drivers.
79 more drivers, and more robustness. 79 Such improvements were continued in the 2.5 kernel series, where they added
80 The 2.5 kernel series continued such improvements, and also 80 USB 2.0 support, improved performance, and made the host controller drivers
81 worked on USB 2.0 support, 81 (HCDs) more consistent. They also simplified the API (to make bugs less
82 higher performance, 82 likely) and added internal "kerneldoc" documentation.
83 better consistency between host controller drivers,
84 API simplification (to make bugs less likely),
85 and providing internal "kerneldoc" documentation.
86 </para> 83 </para>
87 84
88 <para>Linux can run inside USB devices as well as on 85 <para>Linux can run inside USB devices as well as on
89 the hosts that control the devices. 86 the hosts that control the devices.
90 Because the Linux 2.x USB support evolved to support mass market 87 But USB device drivers running inside those peripherals
91 platforms such as Apple Macintosh or PC-compatible systems,
92 it didn't address design concerns for those types of USB systems.
93 So it can't be used inside mass-market PDAs, or other peripherals.
94 USB device drivers running inside those Linux peripherals
95 don't do the same things as the ones running inside hosts, 88 don't do the same things as the ones running inside hosts,
96 and so they've been given a different name: 89 so they've been given a different name:
97 they're called <emphasis>gadget drivers</emphasis>. 90 <emphasis>gadget drivers</emphasis>.
98 This document does not present gadget drivers. 91 This document does not cover gadget drivers.
99 </para> 92 </para>
100 93
101 </chapter> 94 </chapter>
@@ -103,17 +96,14 @@
103<chapter id="host"> 96<chapter id="host">
104 <title>USB Host-Side API Model</title> 97 <title>USB Host-Side API Model</title>
105 98
106 <para>Within the kernel, 99 <para>Host-side drivers for USB devices talk to the "usbcore" APIs.
107 host-side drivers for USB devices talk to the "usbcore" APIs. 100 There are two. One is intended for
108 There are two types of public "usbcore" APIs, targetted at two different 101 <emphasis>general-purpose</emphasis> drivers (exposed through
109 layers of USB driver. Those are 102 driver frameworks), and the other is for drivers that are
110 <emphasis>general purpose</emphasis> drivers, exposed through 103 <emphasis>part of the core</emphasis>.
111 driver frameworks such as block, character, or network devices; 104 Such core drivers include the <emphasis>hub</emphasis> driver
112 and drivers that are <emphasis>part of the core</emphasis>, 105 (which manages trees of USB devices) and several different kinds
113 which are involved in managing a USB bus. 106 of <emphasis>host controller drivers</emphasis>,
114 Such core drivers include the <emphasis>hub</emphasis> driver,
115 which manages trees of USB devices, and several different kinds
116 of <emphasis>host controller driver (HCD)</emphasis>,
117 which control individual busses. 107 which control individual busses.
118 </para> 108 </para>
119 109
@@ -122,21 +112,21 @@
122 112
123 <itemizedlist> 113 <itemizedlist>
124 114
125 <listitem><para>USB supports four kinds of data transfer 115 <listitem><para>USB supports four kinds of data transfers
126 (control, bulk, interrupt, and isochronous). Two transfer 116 (control, bulk, interrupt, and isochronous). Two of them (control
127 types use bandwidth as it's available (control and bulk), 117 and bulk) use bandwidth as it's available,
128 while the other two types of transfer (interrupt and isochronous) 118 while the other two (interrupt and isochronous)
129 are scheduled to provide guaranteed bandwidth. 119 are scheduled to provide guaranteed bandwidth.
130 </para></listitem> 120 </para></listitem>
131 121
132 <listitem><para>The device description model includes one or more 122 <listitem><para>The device description model includes one or more
133 "configurations" per device, only one of which is active at a time. 123 "configurations" per device, only one of which is active at a time.
134 Devices that are capable of high speed operation must also support 124 Devices that are capable of high-speed operation must also support
135 full speed configurations, along with a way to ask about the 125 full-speed configurations, along with a way to ask about the
136 "other speed" configurations that might be used. 126 "other speed" configurations which might be used.
137 </para></listitem> 127 </para></listitem>
138 128
139 <listitem><para>Configurations have one or more "interface", each 129 <listitem><para>Configurations have one or more "interfaces", each
140 of which may have "alternate settings". Interfaces may be 130 of which may have "alternate settings". Interfaces may be
141 standardized by USB "Class" specifications, or may be specific to 131 standardized by USB "Class" specifications, or may be specific to
142 a vendor or device.</para> 132 a vendor or device.</para>
@@ -162,7 +152,7 @@
162 </para></listitem> 152 </para></listitem>
163 153
164 <listitem><para>The Linux USB API supports synchronous calls for 154 <listitem><para>The Linux USB API supports synchronous calls for
165 control and bulk messaging. 155 control and bulk messages.
166 It also supports asynchnous calls for all kinds of data transfer, 156 It also supports asynchnous calls for all kinds of data transfer,
167 using request structures called "URBs" (USB Request Blocks). 157 using request structures called "URBs" (USB Request Blocks).
168 </para></listitem> 158 </para></listitem>