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1
2 Linux UWB + Wireless USB + WiNET
3
4 (C) 2005-2006 Intel Corporation
5 Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com>
6
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.
10
11 This program is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15
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.
20
21
22 Please visit http://bughost.org/thewiki/Design-overview.txt-1.8 for
23 updated content.
24
25 * Design-overview.txt-1.8
26
27 This code implements a Ultra Wide Band stack for Linux, as well as
28 drivers for the 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).
31
32 1. Introduction
33 1. HWA: Host Wire adapters, your Wireless USB dongle
34
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
41
42 2. Host Controller life cycle
43
44 3. On the air: beacons and enumerating the radio neighborhood
45
46 4. Device lists
47 5. Bandwidth allocation
48
49 3. Wireless USB Host Controller drivers
50
51 4. Glossary
52
53
54 Introduction
55
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.
60
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.
68
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.
75
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.
80
81 The different logical parts of this driver are:
82
83 *
84
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
88
89 *
90
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.
94
95
96 HWA: Host Wire adapters, your Wireless USB dongle
97
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 (!)
102
103 The HWA itself is broken in two or three main interfaces:
104
105 *
106
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.
110
111 *
112
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.
119
120 *
121
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.
126
127
128 DWA: Device Wired Adaptor, a Wireless USB hub for wired devices
129
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.
134
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.
138
139
140 WHCI: Wireless Host Controller Interface, the PCI WUSB host adapter
141
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.
146
147 There is still no driver support for this, but will be in upcoming
148 releases.
149
150
151 The UWB stack
152
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.
157
158
159 Devices and hosts: the basic structure
160
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.
165
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.
170
171 *
172
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.
177
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.
188
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()/.
193
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.
197
198
199 Host Controller life cycle
200
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()/].
208
209 *
210
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.
216
217 When a dongle is disconnected, /drivers/uwb/hwa-rc.c:hwarc_disconnect()/
218 takes time of tearing everything down safely (or not...).
219
220
221 On the air: beacons and enumerating the radio neighborhood
222
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:
225
226 *
227
228 $ echo 9 0 > /sys/class/uwb_rc/uwb0/beacon
229
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.
237
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].
245
246
247 Device lists
248
249 All UWB devices are kept in the list of the struct bus_type uwb_bus.
250
251
252 Bandwidth allocation
253
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.
261
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.]
270
271
272 Wireless USB Host Controller drivers
273
274 *WARNING* This section needs a lot of work!
275
276 As explained above, there are three different types of HCs in the WUSB
277 world: HWA-HC, DWA-HC and WHCI-HC.
278
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.
282
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
286
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).
290
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.
294
295 *
296
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.
305
306 Now it all depends on external stimuli.
307
308 *New device connection*
309
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
315
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.
322
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.
328
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.
333
334 *Device life cycle and keep alives*
335
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).
345
346 This is done through devconnect:__wusb_check_devs(), which will scan the
347 device list looking for whom needs refreshing.
348
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.
351
352 *Sending and receiving data*
353
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.
357
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.
362
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.
368
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 :)].
372
373 If reading, we don't send data buffers, just the segment headers saying
374 we want to read segments.
375
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.
385
386 Seems simple, but the implementation is not trivial.
387
388 *
389
390 *WARNING* Old!!
391
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.
396
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.
402
403 For IN xfers, we only issue URBs for the segments we want to read and
404 then wait for the xfer result data.
405
406 *URB mapping into xfers*
407
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.
412
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.
417
418
419 Glossary
420
421 *DWA* -- Device Wire Adapter
422
423 USB host, wired for downstream devices, upstream connects wirelessly
424 with Wireless USB.
425
426 *EVENT* -- Response to a command on the NEEP
427
428 *HWA* -- Host Wire Adapter / USB dongle for UWB and Wireless USB
429
430 *NEH* -- Notification/Event Handle
431
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.
435
436 *NEEP* -- Notification/Event EndPoint
437
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.
441
442 *NOTIFICATION* -- Message coming in the NEEP as response to something.
443
444 *RC* -- Radio Control
445
446 Design-overview.txt-1.8 (last edited 2006-11-04 12:22:24 by
447 InakyPerezGonzalez)
448