About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / usb / WUSB-Design-overview.txt

Custom Search

Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

2	Linux UWB + Wireless USB + WiNET
4	   (C) 2005-2006 Intel Corporation
5	   Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
7	   This program is free software; you can redistribute it and/or
8	   modify it under the terms of the GNU General Public License version
9	   2 as published by the Free Software Foundation.
11	   This program is distributed in the hope that it will be useful,
12	   but WITHOUT ANY WARRANTY; without even the implied warranty of
14	   GNU General Public License for more details.
16	   You should have received a copy of the GNU General Public License
17	   along with this program; if not, write to the Free Software
18	   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
19	   02110-1301, USA.
22	Please visit http://bughost.org/thewiki/Design-overview.txt-1.8 for
23	updated content.
25	    * Design-overview.txt-1.8
27	This code implements a Ultra Wide Band stack for Linux, as well as
28	drivers for the USB based UWB radio controllers defined in the
29	Wireless USB 1.0 specification (including Wireless USB host controller
30	and an Intel WiNET controller).
32	   1. Introduction
33	         1. HWA: Host Wire adapters, your Wireless USB dongle
35	         2. DWA: Device Wired Adaptor, a Wireless USB hub for wired
36	            devices
37	         3. WHCI: Wireless Host Controller Interface, the PCI WUSB host
38	            adapter
39	   2. The UWB stack
40	         1. Devices and hosts: the basic structure
42	         2. Host Controller life cycle
44	         3. On the air: beacons and enumerating the radio neighborhood
46	         4. Device lists
47	         5. Bandwidth allocation
49	   3. Wireless USB Host Controller drivers
51	   4. Glossary
54	    Introduction
56	UWB is a wide-band communication protocol that is to serve also as the
57	low-level protocol for others (much like TCP sits on IP). Currently
58	these others are Wireless USB and TCP/IP, but seems Bluetooth and
59	Firewire/1394 are coming along.
61	UWB uses a band from roughly 3 to 10 GHz, transmitting at a max of
62	~-41dB (or 0.074 uW/MHz--geography specific data is still being
63	negotiated w/ regulators, so watch for changes). That band is divided in
64	a bunch of ~1.5 GHz wide channels (or band groups) composed of three
65	subbands/subchannels (528 MHz each). Each channel is independent of each
66	other, so you could consider them different "busses". Initially this
67	driver considers them all a single one.
69	Radio time is divided in 65536 us long /superframes/, each one divided
70	in 256 256us long /MASs/ (Media Allocation Slots), which are the basic
71	time/media allocation units for transferring data. At the beginning of
72	each superframe there is a Beacon Period (BP), where every device
73	transmit its beacon on a single MAS. The length of the BP depends on how
74	many devices are present and the length of their beacons.
76	Devices have a MAC (fixed, 48 bit address) and a device (changeable, 16
77	bit address) and send periodic beacons to advertise themselves and pass
78	info on what they are and do. They advertise their capabilities and a
79	bunch of other stuff.
81	The different logical parts of this driver are:
83	    *
85	      *UWB*: the Ultra-Wide-Band stack -- manages the radio and
86	      associated spectrum to allow for devices sharing it. Allows to
87	      control bandwidth assignment, beaconing, scanning, etc
89	    *
91	      *WUSB*: the layer that sits on top of UWB to provide Wireless USB.
92	      The Wireless USB spec defines means to control a UWB radio and to
93	      do the actual WUSB.
96	      HWA: Host Wire adapters, your Wireless USB dongle
98	WUSB also defines a device called a Host Wire Adaptor (HWA), which in
99	mere terms is a USB dongle that enables your PC to have UWB and Wireless
100	USB. The Wireless USB Host Controller in a HWA looks to the host like a
101	[Wireless] USB controller connected via USB (!)
103	The HWA itself is broken in two or three main interfaces:
105	    *
107	      *RC*: Radio control -- this implements an interface to the
108	      Ultra-Wide-Band radio controller. The driver for this implements a
109	      USB-based UWB Radio Controller to the UWB stack.
111	    *
113	      *HC*: the wireless USB host controller. It looks like a USB host
114	      whose root port is the radio and the WUSB devices connect to it.
115	      To the system it looks like a separate USB host. The driver (will)
116	      implement a USB host controller (similar to UHCI, OHCI or EHCI)
117	      for which the root hub is the radio...To reiterate: it is a USB
118	      controller that is connected via USB instead of PCI.
120	    *
122	      *WINET*: some HW provide a WiNET interface (IP over UWB). This
123	      package provides a driver for it (it looks like a network
124	      interface, winetX). The driver detects when there is a link up for
125	      their type and kick into gear.
128	      DWA: Device Wired Adaptor, a Wireless USB hub for wired devices
130	These are the complement to HWAs. They are a USB host for connecting
131	wired devices, but it is connected to your PC connected via Wireless
132	USB. To the system it looks like yet another USB host. To the untrained
133	eye, it looks like a hub that connects upstream wirelessly.
135	We still offer no support for this; however, it should share a lot of
136	code with the HWA-RC driver; there is a bunch of factorization work that
137	has been done to support that in upcoming releases.
140	      WHCI: Wireless Host Controller Interface, the PCI WUSB host adapter
142	This is your usual PCI device that implements WHCI. Similar in concept
143	to EHCI, it allows your wireless USB devices (including DWAs) to connect
144	to your host via a PCI interface. As in the case of the HWA, it has a
145	Radio Control interface and the WUSB Host Controller interface per se.
147	There is still no driver support for this, but will be in upcoming
148	releases.
151	    The UWB stack
153	The main mission of the UWB stack is to keep a tally of which devices
154	are in radio proximity to allow drivers to connect to them. As well, it
155	provides an API for controlling the local radio controllers (RCs from
156	now on), such as to start/stop beaconing, scan, allocate bandwidth, etc.
159	      Devices and hosts: the basic structure
161	The main building block here is the UWB device (struct uwb_dev). For
162	each device that pops up in radio presence (ie: the UWB host receives a
163	beacon from it) you get a struct uwb_dev that will show up in
164	/sys/class/uwb and in /sys/bus/uwb/devices.
166	For each RC that is detected, a new struct uwb_rc is created. In turn, a
167	RC is also a device, so they also show in /sys/class/uwb and
168	/sys/bus/uwb/devices, but at the same time, only radio controllers show
169	up in /sys/class/uwb_rc.
171	    *
173	      [*] The reason for RCs being also devices is that not only we can
174	      see them while enumerating the system device tree, but also on the
175	      radio (their beacons and stuff), so the handling has to be
176	      likewise to that of a device.
178	Each RC driver is implemented by a separate driver that plugs into the
179	interface that the UWB stack provides through a struct uwb_rc_ops. The
180	spec creators have been nice enough to make the message format the same
181	for HWA and WHCI RCs, so the driver is really a very thin transport that
182	moves the requests from the UWB API to the device [/uwb_rc_ops->cmd()/]
183	and sends the replies and notifications back to the API
184	[/uwb_rc_neh_grok()/]. Notifications are handled to the UWB daemon, that
185	is chartered, among other things, to keep the tab of how the UWB radio
186	neighborhood looks, creating and destroying devices as they show up or
187	disappear.
189	Command execution is very simple: a command block is sent and a event
190	block or reply is expected back. For sending/receiving command/events, a
191	handle called /neh/ (Notification/Event Handle) is opened with
192	/uwb_rc_neh_open()/.
194	The HWA-RC (USB dongle) driver (drivers/uwb/hwa-rc.c) does this job for
195	the USB connected HWA. Eventually, drivers/whci-rc.c will do the same
196	for the PCI connected WHCI controller.
199	      Host Controller life cycle
201	So let's say we connect a dongle to the system: it is detected and
202	firmware uploaded if needed [for Intel's i1480
203	/drivers/uwb/ptc/usb.c:ptc_usb_probe()/] and then it is reenumerated.
204	Now we have a real HWA device connected and
205	/drivers/uwb/hwa-rc.c:hwarc_probe()/ picks it up, that will set up the
206	Wire-Adaptor environment and then suck it into the UWB stack's vision of
207	the world [/drivers/uwb/lc-rc.c:uwb_rc_add()/].
209	    *
211	      [*] The stack should put a new RC to scan for devices
212	      [/uwb_rc_scan()/] so it finds what's available around and tries to
213	      connect to them, but this is policy stuff and should be driven
214	      from user space. As of now, the operator is expected to do it
215	      manually; see the release notes for documentation on the procedure.
217	When a dongle is disconnected, /drivers/uwb/hwa-rc.c:hwarc_disconnect()/
218	takes time of tearing everything down safely (or not...).
221	      On the air: beacons and enumerating the radio neighborhood
223	So assuming we have devices and we have agreed for a channel to connect
224	on (let's say 9), we put the new RC to beacon:
226	    *
228	            $ echo 9 0 > /sys/class/uwb_rc/uwb0/beacon
230	Now it is visible. If there were other devices in the same radio channel
231	and beacon group (that's what the zero is for), the dongle's radio
232	control interface will send beacon notifications on its
233	notification/event endpoint (NEEP). The beacon notifications are part of
234	the event stream that is funneled into the API with
235	/drivers/uwb/neh.c:uwb_rc_neh_grok()/ and delivered to the UWBD, the UWB
236	daemon through a notification list.
238	UWBD wakes up and scans the event list; finds a beacon and adds it to
239	the BEACON CACHE (/uwb_beca/). If he receives a number of beacons from
240	the same device, he considers it to be 'onair' and creates a new device
241	[/drivers/uwb/lc-dev.c:uwbd_dev_onair()/]. Similarly, when no beacons
242	are received in some time, the device is considered gone and wiped out
243	[uwbd calls periodically /uwb/beacon.c:uwb_beca_purge()/ that will purge
244	the beacon cache of dead devices].
247	      Device lists
249	All UWB devices are kept in the list of the struct bus_type uwb_bus.
252	      Bandwidth allocation
254	The UWB stack maintains a local copy of DRP availability through
255	processing of incoming *DRP Availability Change* notifications. This
256	local copy is currently used to present the current bandwidth
257	availability to the user through the sysfs file
258	/sys/class/uwb_rc/uwbx/bw_avail. In the future the bandwidth
259	availability information will be used by the bandwidth reservation
260	routines.
262	The bandwidth reservation routines are in progress and are thus not
263	present in the current release. When completed they will enable a user
264	to initiate DRP reservation requests through interaction with sysfs. DRP
265	reservation requests from remote UWB devices will also be handled. The
266	bandwidth management done by the UWB stack will include callbacks to the
267	higher layers will enable the higher layers to use the reservations upon
268	completion. [Note: The bandwidth reservation work is in progress and
269	subject to change.]
272	    Wireless USB Host Controller drivers
274	*WARNING* This section needs a lot of work!
276	As explained above, there are three different types of HCs in the WUSB
277	world: HWA-HC, DWA-HC and WHCI-HC.
279	HWA-HC and DWA-HC share that they are Wire-Adapters (USB or WUSB
280	connected controllers), and their transfer management system is almost
281	identical. So is their notification delivery system.
283	HWA-HC and WHCI-HC share that they are both WUSB host controllers, so
284	they have to deal with WUSB device life cycle and maintenance, wireless
285	root-hub
287	HWA exposes a Host Controller interface (HWA-HC 0xe0/02/02). This has
288	three endpoints (Notifications, Data Transfer In and Data Transfer
289	Out--known as NEP, DTI and DTO in the code).
291	We reserve UWB bandwidth for our Wireless USB Cluster, create a Cluster
292	ID and tell the HC to use all that. Then we start it. This means the HC
293	starts sending MMCs.
295	    *
297	      The MMCs are blocks of data defined somewhere in the WUSB1.0 spec
298	      that define a stream in the UWB channel time allocated for sending
299	      WUSB IEs (host to device commands/notifications) and Device
300	      Notifications (device initiated to host). Each host defines a
301	      unique Wireless USB cluster through MMCs. Devices can connect to a
302	      single cluster at the time. The IEs are Information Elements, and
303	      among them are the bandwidth allocations that tell each device
304	      when can they transmit or receive.
306	Now it all depends on external stimuli.
308	*New device connection*
310	A new device pops up, it scans the radio looking for MMCs that give out
311	the existence of Wireless USB channels. Once one (or more) are found,
312	selects which one to connect to. Sends a /DN_Connect/ (device
313	notification connect) during the DNTS (Device Notification Time
314	Slot--announced in the MMCs
316	HC picks the /DN_Connect/ out (nep module sends to notif.c for delivery
317	into /devconnect/). This process starts the authentication process for
318	the device. First we allocate a /fake port/ and assign an
319	unauthenticated address (128 to 255--what we really do is
320	0x80 | fake_port_idx). We fiddle with the fake port status and /khubd/
321	sees a new connection, so he moves on to enable the fake port with a reset.
323	So now we are in the reset path -- we know we have a non-yet enumerated
324	device with an unauthorized address; we ask user space to authenticate
325	(FIXME: not yet done, similar to bluetooth pairing), then we do the key
326	exchange (FIXME: not yet done) and issue a /set address 0/ to bring the
327	device to the default state. Device is authenticated.
329	From here, the USB stack takes control through the usb_hcd ops. khubd
330	has seen the port status changes, as we have been toggling them. It will
331	start enumerating and doing transfers through usb_hcd->urb_enqueue() to
332	read descriptors and move our data.
334	*Device life cycle and keep alives*
336	Every time there is a successful transfer to/from a device, we update a
337	per-device activity timestamp. If not, every now and then we check and
338	if the activity timestamp gets old, we ping the device by sending it a
339	Keep Alive IE; it responds with a /DN_Alive/ pong during the DNTS (this
340	arrives to us as a notification through
341	devconnect.c:wusb_handle_dn_alive(). If a device times out, we
342	disconnect it from the system (cleaning up internal information and
343	toggling the bits in the fake hub port, which kicks khubd into removing
344	the rest of the stuff).
346	This is done through devconnect:__wusb_check_devs(), which will scan the
347	device list looking for whom needs refreshing.
349	If the device wants to disconnect, it will either die (ugly) or send a
350	/DN_Disconnect/ that will prompt a disconnection from the system.
352	*Sending and receiving data*
354	Data is sent and received through /Remote Pipes/ (rpipes). An rpipe is
355	/aimed/ at an endpoint in a WUSB device. This is the same for HWAs and
356	DWAs.
358	Each HC has a number of rpipes and buffers that can be assigned to them;
359	when doing a data transfer (xfer), first the rpipe has to be aimed and
360	prepared (buffers assigned), then we can start queueing requests for
361	data in or out.
363	Data buffers have to be segmented out before sending--so we send first a
364	header (segment request) and then if there is any data, a data buffer
365	immediately after to the DTI interface (yep, even the request). If our
366	buffer is bigger than the max segment size, then we just do multiple
367	requests.
369	[This sucks, because doing USB scatter gatter in Linux is resource
370	intensive, if any...not that the current approach is not. It just has to
371	be cleaned up a lot :)].
373	If reading, we don't send data buffers, just the segment headers saying
374	we want to read segments.
376	When the xfer is executed, we receive a notification that says data is
377	ready in the DTI endpoint (handled through
378	xfer.c:wa_handle_notif_xfer()). In there we read from the DTI endpoint a
379	descriptor that gives us the status of the transfer, its identification
380	(given when we issued it) and the segment number. If it was a data read,
381	we issue another URB to read into the destination buffer the chunk of
382	data coming out of the remote endpoint. Done, wait for the next guy. The
383	callbacks for the URBs issued from here are the ones that will declare
384	the xfer complete at some point and call its callback.
386	Seems simple, but the implementation is not trivial.
388	    *
390	      *WARNING* Old!!
392	The main xfer descriptor, wa_xfer (equivalent to a URB) contains an
393	array of segments, tallys on segments and buffers and callback
394	information. Buried in there is a lot of URBs for executing the segments
395	and buffer transfers.
397	For OUT xfers, there is an array of segments, one URB for each, another
398	one of buffer URB. When submitting, we submit URBs for segment request
399	1, buffer 1, segment 2, buffer 2...etc. Then we wait on the DTI for xfer
400	result data; when all the segments are complete, we call the callback to
401	finalize the transfer.
403	For IN xfers, we only issue URBs for the segments we want to read and
404	then wait for the xfer result data.
406	*URB mapping into xfers*
408	This is done by hwahc_op_urb_[en|de]queue(). In enqueue() we aim an
409	rpipe to the endpoint where we have to transmit, create a transfer
410	context (wa_xfer) and submit it. When the xfer is done, our callback is
411	called and we assign the status bits and release the xfer resources.
413	In dequeue() we are basically cancelling/aborting the transfer. We issue
414	a xfer abort request to the HC, cancel all the URBs we had submitted
415	and not yet done and when all that is done, the xfer callback will be
416	called--this will call the URB callback.
419	    Glossary
421	*DWA* -- Device Wire Adapter
423	USB host, wired for downstream devices, upstream connects wirelessly
424	with Wireless USB.
426	*EVENT* -- Response to a command on the NEEP
428	*HWA* -- Host Wire Adapter / USB dongle for UWB and Wireless USB
430	*NEH* -- Notification/Event Handle
432	Handle/file descriptor for receiving notifications or events. The WA
433	code requires you to get one of this to listen for notifications or
434	events on the NEEP.
436	*NEEP* -- Notification/Event EndPoint
438	Stuff related to the management of the first endpoint of a HWA USB
439	dongle that is used to deliver an stream of events and notifications to
440	the host.
442	*NOTIFICATION* -- Message coming in the NEEP as response to something.
444	*RC* -- Radio Control
446	Design-overview.txt-1.8 (last edited 2006-11-04 12:22:24 by
447	InakyPerezGonzalez)
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.