linux/Documentation/usb/gadget_serial.txt
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   2                 Linux Gadget Serial Driver v2.0
   3                           11/20/2004
   4                  (updated 8-May-2008 for v2.3)
   5
   6
   7License and Disclaimer
   8----------------------
   9This program is free software; you can redistribute it and/or
  10modify it under the terms of the GNU General Public License as
  11published by the Free Software Foundation; either version 2 of
  12the License, or (at your option) any later version.
  13
  14This program is distributed in the hope that it will be useful,
  15but WITHOUT ANY WARRANTY; without even the implied warranty of
  16MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17GNU General Public License for more details.
  18
  19You should have received a copy of the GNU General Public
  20License along with this program; if not, write to the Free
  21Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  22MA 02111-1307 USA.
  23
  24This document and the gadget serial driver itself are
  25Copyright (C) 2004 by Al Borchers (alborchers@steinerpoint.com).
  26
  27If you have questions, problems, or suggestions for this driver
  28please contact Al Borchers at alborchers@steinerpoint.com.
  29
  30
  31Prerequisites
  32-------------
  33Versions of the gadget serial driver are available for the
  342.4 Linux kernels, but this document assumes you are using
  35version 2.3 or later of the gadget serial driver in a 2.6
  36Linux kernel.
  37
  38This document assumes that you are familiar with Linux and
  39Windows and know how to configure and build Linux kernels, run
  40standard utilities, use minicom and HyperTerminal, and work with
  41USB and serial devices.  It also assumes you configure the Linux
  42gadget and usb drivers as modules.
  43
  44With version 2.3 of the driver, major and minor device nodes are
  45no longer statically defined.  Your Linux based system should mount
  46sysfs in /sys, and use "mdev" (in Busybox) or "udev" to make the
  47/dev nodes matching the sysfs /sys/class/tty files.
  48
  49
  50
  51Overview
  52--------
  53The gadget serial driver is a Linux USB gadget driver, a USB device
  54side driver.  It runs on a Linux system that has USB device side
  55hardware; for example, a PDA, an embedded Linux system, or a PC
  56with a USB development card.
  57
  58The gadget serial driver talks over USB to either a CDC ACM driver
  59or a generic USB serial driver running on a host PC.
  60
  61   Host
  62   --------------------------------------
  63  | Host-Side   CDC ACM       USB Host   |
  64  | Operating |   or        | Controller |   USB
  65  | System    | Generic USB | Driver     |--------
  66  | (Linux or | Serial      | and        |        |
  67  | Windows)    Driver        USB Stack  |        |
  68   --------------------------------------         |
  69                                                  |
  70                                                  |
  71                                                  |
  72   Gadget                                         |
  73   --------------------------------------         |
  74  | Gadget                   USB Periph. |        |
  75  | Device-Side |  Gadget  | Controller  |        |
  76  | Linux       |  Serial  | Driver      |--------
  77  | Operating   |  Driver  | and         |
  78  | System                   USB Stack   |
  79   --------------------------------------
  80
  81On the device-side Linux system, the gadget serial driver looks
  82like a serial device.
  83
  84On the host-side system, the gadget serial device looks like a
  85CDC ACM compliant class device or a simple vendor specific device
  86with bulk in and bulk out endpoints, and it is treated similarly
  87to other serial devices.
  88
  89The host side driver can potentially be any ACM compliant driver
  90or any driver that can talk to a device with a simple bulk in/out
  91interface.  Gadget serial has been tested with the Linux ACM driver,
  92the Windows usbser.sys ACM driver, and the Linux USB generic serial
  93driver.
  94
  95With the gadget serial driver and the host side ACM or generic
  96serial driver running, you should be able to communicate between
  97the host and the gadget side systems as if they were connected by a
  98serial cable.
  99
 100The gadget serial driver only provides simple unreliable data
 101communication.  It does not yet handle flow control or many other
 102features of normal serial devices.
 103
 104
 105Installing the Gadget Serial Driver
 106-----------------------------------
 107To use the gadget serial driver you must configure the Linux gadget
 108side kernel for "Support for USB Gadgets", for a "USB Peripheral
 109Controller" (for example, net2280), and for the "Serial Gadget"
 110driver.  All this are listed under "USB Gadget Support" when
 111configuring the kernel.  Then rebuild and install the kernel or
 112modules.
 113
 114Then you must load the gadget serial driver.  To load it as an
 115ACM device (recommended for interoperability), do this:
 116
 117  modprobe g_serial
 118
 119To load it as a vendor specific bulk in/out device, do this:
 120
 121  modprobe g_serial use_acm=0
 122
 123This will also automatically load the underlying gadget peripheral
 124controller driver.  This must be done each time you reboot the gadget
 125side Linux system.  You can add this to the start up scripts, if
 126desired.
 127
 128Your system should use mdev (from busybox) or udev to make the
 129device nodes.  After this gadget driver has been set up you should
 130then see a /dev/ttyGS0 node:
 131
 132  # ls -l /dev/ttyGS0 | cat
 133  crw-rw----    1 root     root     253,   0 May  8 14:10 /dev/ttyGS0
 134  #
 135
 136Note that the major number (253, above) is system-specific.  If
 137you need to create /dev nodes by hand, the right numbers to use
 138will be in the /sys/class/tty/ttyGS0/dev file.
 139
 140When you link this gadget driver early, perhaps even statically,
 141you may want to set up an /etc/inittab entry to run "getty" on it.
 142The /dev/ttyGS0 line should work like most any other serial port.
 143
 144
 145If gadget serial is loaded as an ACM device you will want to use
 146either the Windows or Linux ACM driver on the host side.  If gadget
 147serial is loaded as a bulk in/out device, you will want to use the
 148Linux generic serial driver on the host side.  Follow the appropriate
 149instructions below to install the host side driver.
 150
 151
 152Installing the Windows Host ACM Driver
 153--------------------------------------
 154To use the Windows ACM driver you must have the "linux-cdc-acm.inf"
 155file (provided along this document) which supports all recent versions
 156of Windows.
 157
 158When the gadget serial driver is loaded and the USB device connected
 159to the Windows host with a USB cable, Windows should recognize the
 160gadget serial device and ask for a driver.  Tell Windows to find the
 161driver in the folder that contains the "linux-cdc-acm.inf" file.
 162
 163For example, on Windows XP, when the gadget serial device is first
 164plugged in, the "Found New Hardware Wizard" starts up.  Select
 165"Install from a list or specific location (Advanced)", then on the
 166next screen select "Include this location in the search" and enter the
 167path or browse to the folder containing the "linux-cdc-acm.inf" file.
 168Windows will complain that the Gadget Serial driver has not passed
 169Windows Logo testing, but select "Continue anyway" and finish the
 170driver installation.
 171
 172On Windows XP, in the "Device Manager" (under "Control Panel",
 173"System", "Hardware") expand the "Ports (COM & LPT)" entry and you
 174should see "Gadget Serial" listed as the driver for one of the COM
 175ports.
 176
 177To uninstall the Windows XP driver for "Gadget Serial", right click
 178on the "Gadget Serial" entry in the "Device Manager" and select
 179"Uninstall".
 180
 181
 182Installing the Linux Host ACM Driver
 183------------------------------------
 184To use the Linux ACM driver you must configure the Linux host side
 185kernel for "Support for Host-side USB" and for "USB Modem (CDC ACM)
 186support".
 187
 188Once the gadget serial driver is loaded and the USB device connected
 189to the Linux host with a USB cable, the host system should recognize
 190the gadget serial device.  For example, the command
 191
 192  cat /proc/bus/usb/devices
 193
 194should show something like this:
 195
 196T:  Bus=01 Lev=01 Prnt=01 Port=01 Cnt=02 Dev#=  5 Spd=480 MxCh= 0
 197D:  Ver= 2.00 Cls=02(comm.) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
 198P:  Vendor=0525 ProdID=a4a7 Rev= 2.01
 199S:  Manufacturer=Linux 2.6.8.1 with net2280
 200S:  Product=Gadget Serial
 201S:  SerialNumber=0
 202C:* #Ifs= 2 Cfg#= 2 Atr=c0 MxPwr=  2mA
 203I:  If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=02 Prot=01 Driver=acm
 204E:  Ad=83(I) Atr=03(Int.) MxPS=   8 Ivl=32ms
 205I:  If#= 1 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=acm
 206E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
 207E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
 208
 209If the host side Linux system is configured properly, the ACM driver
 210should be loaded automatically.  The command "lsmod" should show the
 211"acm" module is loaded.
 212
 213
 214Installing the Linux Host Generic USB Serial Driver
 215---------------------------------------------------
 216To use the Linux generic USB serial driver you must configure the
 217Linux host side kernel for "Support for Host-side USB", for "USB
 218Serial Converter support", and for the "USB Generic Serial Driver".
 219
 220Once the gadget serial driver is loaded and the USB device connected
 221to the Linux host with a USB cable, the host system should recognize
 222the gadget serial device.  For example, the command
 223
 224  cat /proc/bus/usb/devices
 225
 226should show something like this:
 227
 228T:  Bus=01 Lev=01 Prnt=01 Port=01 Cnt=02 Dev#=  6 Spd=480 MxCh= 0
 229D:  Ver= 2.00 Cls=ff(vend.) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
 230P:  Vendor=0525 ProdID=a4a6 Rev= 2.01
 231S:  Manufacturer=Linux 2.6.8.1 with net2280
 232S:  Product=Gadget Serial
 233S:  SerialNumber=0
 234C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=  2mA
 235I:  If#= 0 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=serial
 236E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
 237E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
 238
 239You must explicitly load the usbserial driver with parameters to
 240configure it to recognize the gadget serial device, like this:
 241
 242  modprobe usbserial vendor=0x0525 product=0xA4A6
 243
 244If everything is working, usbserial will print a message in the
 245system log saying something like "Gadget Serial converter now
 246attached to ttyUSB0".
 247
 248
 249Testing with Minicom or HyperTerminal
 250-------------------------------------
 251Once the gadget serial driver and the host driver are both installed,
 252and a USB cable connects the gadget device to the host, you should
 253be able to communicate over USB between the gadget and host systems.
 254You can use minicom or HyperTerminal to try this out.
 255
 256On the gadget side run "minicom -s" to configure a new minicom
 257session.  Under "Serial port setup" set "/dev/ttygserial" as the
 258"Serial Device".  Set baud rate, data bits, parity, and stop bits,
 259to 9600, 8, none, and 1--these settings mostly do not matter.
 260Under "Modem and dialing" erase all the modem and dialing strings.
 261
 262On a Linux host running the ACM driver, configure minicom similarly
 263but use "/dev/ttyACM0" as the "Serial Device".  (If you have other
 264ACM devices connected, change the device name appropriately.)
 265
 266On a Linux host running the USB generic serial driver, configure
 267minicom similarly, but use "/dev/ttyUSB0" as the "Serial Device".
 268(If you have other USB serial devices connected, change the device
 269name appropriately.)
 270
 271On a Windows host configure a new HyperTerminal session to use the
 272COM port assigned to Gadget Serial.  The "Port Settings" will be
 273set automatically when HyperTerminal connects to the gadget serial
 274device, so you can leave them set to the default values--these
 275settings mostly do not matter.
 276
 277With minicom configured and running on the gadget side and with
 278minicom or HyperTerminal configured and running on the host side,
 279you should be able to send data back and forth between the gadget
 280side and host side systems.  Anything you type on the terminal
 281window on the gadget side should appear in the terminal window on
 282the host side and vice versa.
 283
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