Based on kernel version 3.12. Page generated on 2013-11-13 22:00 EST.
1 2 Linux UWB + Wireless USB + WiNET 3 4 (C) 2005-2006 Intel Corporation 5 Inaky Perez-Gonzalez <firstname.lastname@example.org> 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)