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