gadget_multi.rst (5673B)
1============================== 2Multifunction Composite Gadget 3============================== 4 5Overview 6======== 7 8The Multifunction Composite Gadget (or g_multi) is a composite gadget 9that makes extensive use of the composite framework to provide 10a... multifunction gadget. 11 12In it's standard configuration it provides a single USB configuration 13with RNDIS[1] (that is Ethernet), USB CDC[2] ACM (that is serial) and 14USB Mass Storage functions. 15 16A CDC ECM (Ethernet) function may be turned on via a Kconfig option 17and RNDIS can be turned off. If they are both enabled the gadget will 18have two configurations -- one with RNDIS and another with CDC ECM[3]. 19 20Please note that if you use non-standard configuration (that is enable 21CDC ECM) you may need to change vendor and/or product ID. 22 23Host drivers 24============ 25 26To make use of the gadget one needs to make it work on host side -- 27without that there's no hope of achieving anything with the gadget. 28As one might expect, things one need to do very from system to system. 29 30Linux host drivers 31------------------ 32 33Since the gadget uses standard composite framework and appears as such 34to Linux host it does not need any additional drivers on Linux host 35side. All the functions are handled by respective drivers developed 36for them. 37 38This is also true for two configuration set-up with RNDIS 39configuration being the first one. Linux host will use the second 40configuration with CDC ECM which should work better under Linux. 41 42Windows host drivers 43-------------------- 44 45For the gadget to work under Windows two conditions have to be met: 46 47Detecting as composite gadget 48^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 49 50First of all, Windows need to detect the gadget as an USB composite 51gadget which on its own have some conditions[4]. If they are met, 52Windows lets USB Generic Parent Driver[5] handle the device which then 53tries to match drivers for each individual interface (sort of, don't 54get into too many details). 55 56The good news is: you do not have to worry about most of the 57conditions! 58 59The only thing to worry is that the gadget has to have a single 60configuration so a dual RNDIS and CDC ECM gadget won't work unless you 61create a proper INF -- and of course, if you do submit it! 62 63Installing drivers for each function 64^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 65 66The other, trickier thing is making Windows install drivers for each 67individual function. 68 69For mass storage it is trivial since Windows detect it's an interface 70implementing USB Mass Storage class and selects appropriate driver. 71 72Things are harder with RDNIS and CDC ACM. 73 74RNDIS 75..... 76 77To make Windows select RNDIS drivers for the first function in the 78gadget, one needs to use the [[file:linux.inf]] file provided with this 79document. It "attaches" Window's RNDIS driver to the first interface 80of the gadget. 81 82Please note, that while testing we encountered some issues[6] when 83RNDIS was not the first interface. You do not need to worry abut it 84unless you are trying to develop your own gadget in which case watch 85out for this bug. 86 87CDC ACM 88....... 89 90Similarly, [[file:linux-cdc-acm.inf]] is provided for CDC ACM. 91 92Customising the gadget 93...................... 94 95If you intend to hack the g_multi gadget be advised that rearranging 96functions will obviously change interface numbers for each of the 97functionality. As an effect provided INFs won't work since they have 98interface numbers hard-coded in them (it's not hard to change those 99though[7]). 100 101This also means, that after experimenting with g_multi and changing 102provided functions one should change gadget's vendor and/or product ID 103so there will be no collision with other customised gadgets or the 104original gadget. 105 106Failing to comply may cause brain damage after wondering for hours why 107things don't work as intended before realising Windows have cached 108some drivers information (changing USB port may sometimes help plus 109you might try using USBDeview[8] to remove the phantom device). 110 111INF testing 112........... 113 114Provided INF files have been tested on Windows XP SP3, Windows Vista 115and Windows 7, all 32-bit versions. It should work on 64-bit versions 116as well. It most likely won't work on Windows prior to Windows XP 117SP2. 118 119Other systems 120------------- 121 122At this moment, drivers for any other systems have not been tested. 123Knowing how MacOS is based on BSD and BSD is an Open Source it is 124believed that it should (read: "I have no idea whether it will") work 125out-of-the-box. 126 127For more exotic systems I have even less to say... 128 129Any testing and drivers *are* *welcome*! 130 131Authors 132======= 133 134This document has been written by Michal Nazarewicz 135([[mailto:mina86@mina86.com]]). INF files have been hacked with 136support of Marek Szyprowski ([[mailto:m.szyprowski@samsung.com]]) and 137Xiaofan Chen ([[mailto:xiaofanc@gmail.com]]) basing on the MS RNDIS 138template[9], Microchip's CDC ACM INF file and David Brownell's 139([[mailto:dbrownell@users.sourceforge.net]]) original INF files. 140 141Footnotes 142========= 143 144[1] Remote Network Driver Interface Specification, 145[[https://msdn.microsoft.com/en-us/library/ee484414.aspx]]. 146 147[2] Communications Device Class Abstract Control Model, spec for this 148and other USB classes can be found at 149[[http://www.usb.org/developers/devclass_docs/]]. 150 151[3] CDC Ethernet Control Model. 152 153[4] [[https://msdn.microsoft.com/en-us/library/ff537109(v=VS.85).aspx]] 154 155[5] [[https://msdn.microsoft.com/en-us/library/ff539234(v=VS.85).aspx]] 156 157[6] To put it in some other nice words, Windows failed to respond to 158any user input. 159 160[7] You may find [[http://www.cygnal.org/ubb/Forum9/HTML/001050.html]] 161useful. 162 163[8] https://www.nirsoft.net/utils/usb_devices_view.html 164 165[9] [[https://msdn.microsoft.com/en-us/library/ff570620.aspx]]