-*- org -*-
  
  * Overview
  
  The Multifunction Composite Gadget (or g_multi) is a composite gadget
  that makes extensive use of the composite framework to provide
  a... multifunction gadget.
  
  In it's standard configuration it provides a single USB configuration
  with RNDIS[1] (that is Ethernet), USB CDC[2] ACM (that is serial) and
  USB Mass Storage functions.
  
  A CDC ECM (Ethernet) function may be turned on via a Kconfig option
  and RNDIS can be turned off.  If they are both enabled the gadget will
  have two configurations -- one with RNDIS and another with CDC ECM[3].
  
  Please not that if you use non-standard configuration (that is enable
  CDC ECM) you may need to change vendor and/or product ID.
  
  * Host drivers
  
  To make use of the gadget one needs to make it work on host side --
  without that there's no hope of achieving anything with the gadget.
  As one might expect, things one need to do very from system to system.
  
  ** Linux host drivers
  
  Since the gadget uses standard composite framework and appears as such
  to Linux host it does not need any additional drivers on Linux host
  side.  All the functions are handled by respective drivers developed
  for them.
  
  This is also true for two configuration set-up with RNDIS
  configuration being the first one.  Linux host will use the second
  configuration with CDC ECM which should work better under Linux.
  
  ** Windows host drivers
  
  For the gadget two work under Windows two conditions have to be met:
  
  *** Detecting as composite gadget
  
  First of all, Windows need to detect the gadget as an USB composite
  gadget which on its own have some conditions[4].  If they are met,
  Windows lets USB Generic Parent Driver[5] handle the device which then
  tries to much drivers for each individual interface (sort of, don't
  get into too many details).
  
  The good news is: you do not have to worry about most of the
  conditions!
  
  The only thing to worry is that the gadget has to have a single
  configuration so a dual RNDIS and CDC ECM gadget won't work unless you
  create a proper INF -- and of course, if you do submit it!
  
  *** Installing drivers for each function
  
  The other, trickier thing is making Windows install drivers for each
  individual function.
  
  For mass storage it is trivial since Windows detect it's an interface
  implementing USB Mass Storage class and selects appropriate driver.
  
  Things are harder with RDNIS and CDC ACM.
  
  **** RNDIS
  
  To make Windows select RNDIS drivers for the first function in the
  gadget, one needs to use the [[file:linux.inf]] file provided with this
  document.  It "attaches" Window's RNDIS driver to the first interface
  of the gadget.
  
  Please note, that while testing we encountered some issues[6] when
  RNDIS was not the first interface.  You do not need to worry abut it
  unless you are trying to develop your own gadget in which case watch
  out for this bug.
  
  **** CDC ACM
  
  Similarly, [[file:linux-cdc-acm.inf]] is provided for CDC ACM.
  
  **** Customising the gadget
  
  If you intend to hack the g_multi gadget be advised that rearranging
  functions will obviously change interface numbers for each of the
  functionality.  As an effect provided INFs won't work since they have
  interface numbers hard-coded in them (it's not hard to change those
  though[7]).
  
  This also means, that after experimenting with g_multi and changing
  provided functions one should change gadget's vendor and/or product ID
  so there will be no collision with other customised gadgets or the
  original gadget.
  
  Failing to comply may cause brain damage after wondering for hours why
  things don't work as intended before realising Windows have cached
  some drivers information (changing USB port may sometimes help plus
  you might try using USBDeview[8] to remove the phantom device).
  
  **** INF testing
  
  Provided INF files have been tested on Windows XP SP3, Windows Vista
  and Windows 7, all 32-bit versions.  It should work on 64-bit versions
  as well.  It most likely won't work on Windows prior to Windows XP
  SP2.
  
  ** Other systems
  
  At this moment, drivers for any other systems have not been tested.
  Knowing how MacOS is based on BSD and BSD is an Open Source it is
  believed that it should (read: "I have no idea whether it will") work
  out-of-the-box.
  
  For more exotic systems I have even less to say...
  
  Any testing and drivers *are* *welcome*!
  
  * Authors
  
  This document has been written by Michal Nazarewicz
  ([[mailto:mina86@mina86.com]]).  INF files have been hacked with
  support of Marek Szyprowski ([[mailto:m.szyprowski@samsung.com]]) and
  Xiaofan Chen ([[mailto:xiaofanc@gmail.com]]) basing on the MS RNDIS
  template[9], Microchip's CDC ACM INF file and David Brownell's
  ([[mailto:dbrownell@users.sourceforge.net]]) original INF files.
  
  * Footnotes
  
  [1] Remote Network Driver Interface Specification,
  [[http://msdn.microsoft.com/en-us/library/ee484414.aspx]].
  
  [2] Communications Device Class Abstract Control Model, spec for this
  and other USB classes can be found at
  [[http://www.usb.org/developers/devclass_docs/]].
  
  [3] CDC Ethernet Control Model.
  
  [4] [[http://msdn.microsoft.com/en-us/library/ff537109(v=VS.85).aspx]]
  
  [5] [[http://msdn.microsoft.com/en-us/library/ff539234(v=VS.85).aspx]]
  
  [6] To put it in some other nice words, Windows failed to respond to
  any user input.
  
  [7] You may find [[http://www.cygnal.org/ubb/Forum9/HTML/001050.html]]
  useful.
  
  [8] http://www.nirsoft.net/utils/usb_devices_view.html
  
  [9] [[http://msdn.microsoft.com/en-us/library/ff570620.aspx]]