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+
+                 Linux Gadget Serial Driver v2.0
+                           11/20/2004
+                  (updated 8-May-2008 for v2.3)
+
+
+License and Disclaimer
+----------------------
+This program is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License as
+published by the Free Software Foundation; either version 2 of
+the License, or (at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public
+License along with this program; if not, write to the Free
+Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+MA 02111-1307 USA.
+
+This document and the gadget serial driver itself are
+Copyright (C) 2004 by Al Borchers (alborchers@steinerpoint.com).
+
+If you have questions, problems, or suggestions for this driver
+please contact Al Borchers at alborchers@steinerpoint.com.
+
+
+Prerequisites
+-------------
+Versions of the gadget serial driver are available for the
+2.4 Linux kernels, but this document assumes you are using
+version 2.3 or later of the gadget serial driver in a 2.6
+Linux kernel.
+
+This document assumes that you are familiar with Linux and
+Windows and know how to configure and build Linux kernels, run
+standard utilities, use minicom and HyperTerminal, and work with
+USB and serial devices.  It also assumes you configure the Linux
+gadget and usb drivers as modules.
+
+With version 2.3 of the driver, major and minor device nodes are
+no longer statically defined.  Your Linux based system should mount
+sysfs in /sys, and use "mdev" (in Busybox) or "udev" to make the
+/dev nodes matching the sysfs /sys/class/tty files.
+
+
+
+Overview
+--------
+The gadget serial driver is a Linux USB gadget driver, a USB device
+side driver.  It runs on a Linux system that has USB device side
+hardware; for example, a PDA, an embedded Linux system, or a PC
+with a USB development card.
+
+The gadget serial driver talks over USB to either a CDC ACM driver
+or a generic USB serial driver running on a host PC.
+
+   Host
+   --------------------------------------
+  | Host-Side   CDC ACM       USB Host   |
+  | Operating |   or        | Controller |   USB
+  | System    | Generic USB | Driver     |--------
+  | (Linux or | Serial      | and        |        |
+  | Windows)    Driver        USB Stack  |        |
+   --------------------------------------         |
+                                                  |
+                                                  |
+                                                  |
+   Gadget                                         |
+   --------------------------------------         |
+  | Gadget                   USB Periph. |        |
+  | Device-Side |  Gadget  | Controller  |        |
+  | Linux       |  Serial  | Driver      |--------
+  | Operating   |  Driver  | and         |
+  | System                   USB Stack   |
+   --------------------------------------
+
+On the device-side Linux system, the gadget serial driver looks
+like a serial device.
+
+On the host-side system, the gadget serial device looks like a
+CDC ACM compliant class device or a simple vendor specific device
+with bulk in and bulk out endpoints, and it is treated similarly
+to other serial devices.
+
+The host side driver can potentially be any ACM compliant driver
+or any driver that can talk to a device with a simple bulk in/out
+interface.  Gadget serial has been tested with the Linux ACM driver,
+the Windows usbser.sys ACM driver, and the Linux USB generic serial
+driver.
+
+With the gadget serial driver and the host side ACM or generic
+serial driver running, you should be able to communicate between
+the host and the gadget side systems as if they were connected by a
+serial cable.
+
+The gadget serial driver only provides simple unreliable data
+communication.  It does not yet handle flow control or many other
+features of normal serial devices.
+
+
+Installing the Gadget Serial Driver
+-----------------------------------
+To use the gadget serial driver you must configure the Linux gadget
+side kernel for "Support for USB Gadgets", for a "USB Peripheral
+Controller" (for example, net2280), and for the "Serial Gadget"
+driver.  All this are listed under "USB Gadget Support" when
+configuring the kernel.  Then rebuild and install the kernel or
+modules.
+
+Then you must load the gadget serial driver.  To load it as an
+ACM device (recommended for interoperability), do this:
+
+  modprobe g_serial
+
+To load it as a vendor specific bulk in/out device, do this:
+
+  modprobe g_serial use_acm=0
+
+This will also automatically load the underlying gadget peripheral
+controller driver.  This must be done each time you reboot the gadget
+side Linux system.  You can add this to the start up scripts, if
+desired.
+
+Your system should use mdev (from busybox) or udev to make the
+device nodes.  After this gadget driver has been set up you should
+then see a /dev/ttyGS0 node:
+
+  # ls -l /dev/ttyGS0 | cat
+  crw-rw----    1 root     root     253,   0 May  8 14:10 /dev/ttyGS0
+  #
+
+Note that the major number (253, above) is system-specific.  If
+you need to create /dev nodes by hand, the right numbers to use
+will be in the /sys/class/tty/ttyGS0/dev file.
+
+When you link this gadget driver early, perhaps even statically,
+you may want to set up an /etc/inittab entry to run "getty" on it.
+The /dev/ttyGS0 line should work like most any other serial port.
+
+
+If gadget serial is loaded as an ACM device you will want to use
+either the Windows or Linux ACM driver on the host side.  If gadget
+serial is loaded as a bulk in/out device, you will want to use the
+Linux generic serial driver on the host side.  Follow the appropriate
+instructions below to install the host side driver.
+
+
+Installing the Windows Host ACM Driver
+--------------------------------------
+To use the Windows ACM driver you must have the "linux-cdc-acm.inf"
+file (provided along this document) which supports all recent versions
+of Windows.
+
+When the gadget serial driver is loaded and the USB device connected
+to the Windows host with a USB cable, Windows should recognize the
+gadget serial device and ask for a driver.  Tell Windows to find the
+driver in the folder that contains the "linux-cdc-acm.inf" file.
+
+For example, on Windows XP, when the gadget serial device is first
+plugged in, the "Found New Hardware Wizard" starts up.  Select
+"Install from a list or specific location (Advanced)", then on the
+next screen select "Include this location in the search" and enter the
+path or browse to the folder containing the "linux-cdc-acm.inf" file.
+Windows will complain that the Gadget Serial driver has not passed
+Windows Logo testing, but select "Continue anyway" and finish the
+driver installation.
+
+On Windows XP, in the "Device Manager" (under "Control Panel",
+"System", "Hardware") expand the "Ports (COM & LPT)" entry and you
+should see "Gadget Serial" listed as the driver for one of the COM
+ports.
+
+To uninstall the Windows XP driver for "Gadget Serial", right click
+on the "Gadget Serial" entry in the "Device Manager" and select
+"Uninstall".
+
+
+Installing the Linux Host ACM Driver
+------------------------------------
+To use the Linux ACM driver you must configure the Linux host side
+kernel for "Support for Host-side USB" and for "USB Modem (CDC ACM)
+support".
+
+Once the gadget serial driver is loaded and the USB device connected
+to the Linux host with a USB cable, the host system should recognize
+the gadget serial device.  For example, the command
+
+  cat /proc/bus/usb/devices
+
+should show something like this:
+
+T:  Bus=01 Lev=01 Prnt=01 Port=01 Cnt=02 Dev#=  5 Spd=480 MxCh= 0
+D:  Ver= 2.00 Cls=02(comm.) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
+P:  Vendor=0525 ProdID=a4a7 Rev= 2.01
+S:  Manufacturer=Linux 2.6.8.1 with net2280
+S:  Product=Gadget Serial
+S:  SerialNumber=0
+C:* #Ifs= 2 Cfg#= 2 Atr=c0 MxPwr=  2mA
+I:  If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=02 Prot=01 Driver=acm
+E:  Ad=83(I) Atr=03(Int.) MxPS=   8 Ivl=32ms
+I:  If#= 1 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=acm
+E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
+E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
+
+If the host side Linux system is configured properly, the ACM driver
+should be loaded automatically.  The command "lsmod" should show the
+"acm" module is loaded.
+
+
+Installing the Linux Host Generic USB Serial Driver
+---------------------------------------------------
+To use the Linux generic USB serial driver you must configure the
+Linux host side kernel for "Support for Host-side USB", for "USB
+Serial Converter support", and for the "USB Generic Serial Driver".
+
+Once the gadget serial driver is loaded and the USB device connected
+to the Linux host with a USB cable, the host system should recognize
+the gadget serial device.  For example, the command
+
+  cat /proc/bus/usb/devices
+
+should show something like this:
+
+T:  Bus=01 Lev=01 Prnt=01 Port=01 Cnt=02 Dev#=  6 Spd=480 MxCh= 0
+D:  Ver= 2.00 Cls=ff(vend.) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
+P:  Vendor=0525 ProdID=a4a6 Rev= 2.01
+S:  Manufacturer=Linux 2.6.8.1 with net2280
+S:  Product=Gadget Serial
+S:  SerialNumber=0
+C:* #Ifs= 1 Cfg#= 1 Atr=c0 MxPwr=  2mA
+I:  If#= 0 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=serial
+E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
+E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
+
+You must load the usbserial driver and explicitly set its parameters
+to configure it to recognize the gadget serial device, like this:
+
+  echo 0x0525 0xA4A6 >/sys/bus/usb-serial/drivers/generic/new_id
+
+The legacy way is to use module parameters:
+
+  modprobe usbserial vendor=0x0525 product=0xA4A6
+
+If everything is working, usbserial will print a message in the
+system log saying something like "Gadget Serial converter now
+attached to ttyUSB0".
+
+
+Testing with Minicom or HyperTerminal
+-------------------------------------
+Once the gadget serial driver and the host driver are both installed,
+and a USB cable connects the gadget device to the host, you should
+be able to communicate over USB between the gadget and host systems.
+You can use minicom or HyperTerminal to try this out.
+
+On the gadget side run "minicom -s" to configure a new minicom
+session.  Under "Serial port setup" set "/dev/ttygserial" as the
+"Serial Device".  Set baud rate, data bits, parity, and stop bits,
+to 9600, 8, none, and 1--these settings mostly do not matter.
+Under "Modem and dialing" erase all the modem and dialing strings.
+
+On a Linux host running the ACM driver, configure minicom similarly
+but use "/dev/ttyACM0" as the "Serial Device".  (If you have other
+ACM devices connected, change the device name appropriately.)
+
+On a Linux host running the USB generic serial driver, configure
+minicom similarly, but use "/dev/ttyUSB0" as the "Serial Device".
+(If you have other USB serial devices connected, change the device
+name appropriately.)
+
+On a Windows host configure a new HyperTerminal session to use the
+COM port assigned to Gadget Serial.  The "Port Settings" will be
+set automatically when HyperTerminal connects to the gadget serial
+device, so you can leave them set to the default values--these
+settings mostly do not matter.
+
+With minicom configured and running on the gadget side and with
+minicom or HyperTerminal configured and running on the host side,
+you should be able to send data back and forth between the gadget
+side and host side systems.  Anything you type on the terminal
+window on the gadget side should appear in the terminal window on
+the host side and vice versa.