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diff --git a/Documentation/usb/WUSB-Design-overview.txt b/Documentation/usb/WUSB-Design-overview.txt new file mode 100644 index 0000000..4c3d62c --- /dev/null +++ b/Documentation/usb/WUSB-Design-overview.txt @@ -0,0 +1,448 @@ + +Linux UWB + Wireless USB + WiNET + + (C) 2005-2006 Intel Corporation + Inaky Perez-Gonzalez <inaky.perez-gonzalez@intel.com> + + This program is free software; you can redistribute it and/or + modify it under the terms of the GNU General Public License version + 2 as published by the Free Software Foundation. + + This program is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + GNU General Public License for more details. + + You should have received a copy of the GNU General Public License + along with this program; if not, write to the Free Software + Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA + 02110-1301, USA. + + +Please visit http://bughost.org/thewiki/Design-overview.txt-1.8 for +updated content. + + * Design-overview.txt-1.8 + +This code implements a Ultra Wide Band stack for Linux, as well as +drivers for the the USB based UWB radio controllers defined in the +Wireless USB 1.0 specification (including Wireless USB host controller +and an Intel WiNET controller). + + 1. Introduction + 1. HWA: Host Wire adapters, your Wireless USB dongle + + 2. DWA: Device Wired Adaptor, a Wireless USB hub for wired + devices + 3. WHCI: Wireless Host Controller Interface, the PCI WUSB host + adapter + 2. The UWB stack + 1. Devices and hosts: the basic structure + + 2. Host Controller life cycle + + 3. On the air: beacons and enumerating the radio neighborhood + + 4. Device lists + 5. Bandwidth allocation + + 3. Wireless USB Host Controller drivers + + 4. Glossary + + + Introduction + +UWB is a wide-band communication protocol that is to serve also as the +low-level protocol for others (much like TCP sits on IP). Currently +these others are Wireless USB and TCP/IP, but seems Bluetooth and +Firewire/1394 are coming along. + +UWB uses a band from roughly 3 to 10 GHz, transmitting at a max of +~-41dB (or 0.074 uW/MHz--geography specific data is still being +negotiated w/ regulators, so watch for changes). That band is divided in +a bunch of ~1.5 GHz wide channels (or band groups) composed of three +subbands/subchannels (528 MHz each). Each channel is independent of each +other, so you could consider them different "busses". Initially this +driver considers them all a single one. + +Radio time is divided in 65536 us long /superframes/, each one divided +in 256 256us long /MASs/ (Media Allocation Slots), which are the basic +time/media allocation units for transferring data. At the beginning of +each superframe there is a Beacon Period (BP), where every device +transmit its beacon on a single MAS. The length of the BP depends on how +many devices are present and the length of their beacons. + +Devices have a MAC (fixed, 48 bit address) and a device (changeable, 16 +bit address) and send periodic beacons to advertise themselves and pass +info on what they are and do. They advertise their capabilities and a +bunch of other stuff. + +The different logical parts of this driver are: + + * + + *UWB*: the Ultra-Wide-Band stack -- manages the radio and + associated spectrum to allow for devices sharing it. Allows to + control bandwidth assingment, beaconing, scanning, etc + + * + + *WUSB*: the layer that sits on top of UWB to provide Wireless USB. + The Wireless USB spec defines means to control a UWB radio and to + do the actual WUSB. + + + HWA: Host Wire adapters, your Wireless USB dongle + +WUSB also defines a device called a Host Wire Adaptor (HWA), which in +mere terms is a USB dongle that enables your PC to have UWB and Wireless +USB. The Wireless USB Host Controller in a HWA looks to the host like a +[Wireless] USB controller connected via USB (!) + +The HWA itself is broken in two or three main interfaces: + + * + + *RC*: Radio control -- this implements an interface to the + Ultra-Wide-Band radio controller. The driver for this implements a + USB-based UWB Radio Controller to the UWB stack. + + * + + *HC*: the wireless USB host controller. It looks like a USB host + whose root port is the radio and the WUSB devices connect to it. + To the system it looks like a separate USB host. The driver (will) + implement a USB host controller (similar to UHCI, OHCI or EHCI) + for which the root hub is the radio...To reiterate: it is a USB + controller that is connected via USB instead of PCI. + + * + + *WINET*: some HW provide a WiNET interface (IP over UWB). This + package provides a driver for it (it looks like a network + interface, winetX). The driver detects when there is a link up for + their type and kick into gear. + + + DWA: Device Wired Adaptor, a Wireless USB hub for wired devices + +These are the complement to HWAs. They are a USB host for connecting +wired devices, but it is connected to your PC connected via Wireless +USB. To the system it looks like yet another USB host. To the untrained +eye, it looks like a hub that connects upstream wirelessly. + +We still offer no support for this; however, it should share a lot of +code with the HWA-RC driver; there is a bunch of factorization work that +has been done to support that in upcoming releases. + + + WHCI: Wireless Host Controller Interface, the PCI WUSB host adapter + +This is your usual PCI device that implements WHCI. Similar in concept +to EHCI, it allows your wireless USB devices (including DWAs) to connect +to your host via a PCI interface. As in the case of the HWA, it has a +Radio Control interface and the WUSB Host Controller interface per se. + +There is still no driver support for this, but will be in upcoming +releases. + + + The UWB stack + +The main mission of the UWB stack is to keep a tally of which devices +are in radio proximity to allow drivers to connect to them. As well, it +provides an API for controlling the local radio controllers (RCs from +now on), such as to start/stop beaconing, scan, allocate bandwidth, etc. + + + Devices and hosts: the basic structure + +The main building block here is the UWB device (struct uwb_dev). For +each device that pops up in radio presence (ie: the UWB host receives a +beacon from it) you get a struct uwb_dev that will show up in +/sys/class/uwb and in /sys/bus/uwb/devices. + +For each RC that is detected, a new struct uwb_rc is created. In turn, a +RC is also a device, so they also show in /sys/class/uwb and +/sys/bus/uwb/devices, but at the same time, only radio controllers show +up in /sys/class/uwb_rc. + + * + + [*] The reason for RCs being also devices is that not only we can + see them while enumerating the system device tree, but also on the + radio (their beacons and stuff), so the handling has to be + likewise to that of a device. + +Each RC driver is implemented by a separate driver that plugs into the +interface that the UWB stack provides through a struct uwb_rc_ops. The +spec creators have been nice enough to make the message format the same +for HWA and WHCI RCs, so the driver is really a very thin transport that +moves the requests from the UWB API to the device [/uwb_rc_ops->cmd()/] +and sends the replies and notifications back to the API +[/uwb_rc_neh_grok()/]. Notifications are handled to the UWB daemon, that +is chartered, among other things, to keep the tab of how the UWB radio +neighborhood looks, creating and destroying devices as they show up or +dissapear. + +Command execution is very simple: a command block is sent and a event +block or reply is expected back. For sending/receiving command/events, a +handle called /neh/ (Notification/Event Handle) is opened with +/uwb_rc_neh_open()/. + +The HWA-RC (USB dongle) driver (drivers/uwb/hwa-rc.c) does this job for +the USB connected HWA. Eventually, drivers/whci-rc.c will do the same +for the PCI connected WHCI controller. + + + Host Controller life cycle + +So let's say we connect a dongle to the system: it is detected and +firmware uploaded if needed [for Intel's i1480 +/drivers/uwb/ptc/usb.c:ptc_usb_probe()/] and then it is reenumerated. +Now we have a real HWA device connected and +/drivers/uwb/hwa-rc.c:hwarc_probe()/ picks it up, that will set up the +Wire-Adaptor environment and then suck it into the UWB stack's vision of +the world [/drivers/uwb/lc-rc.c:uwb_rc_add()/]. + + * + + [*] The stack should put a new RC to scan for devices + [/uwb_rc_scan()/] so it finds what's available around and tries to + connect to them, but this is policy stuff and should be driven + from user space. As of now, the operator is expected to do it + manually; see the release notes for documentation on the procedure. + +When a dongle is disconnected, /drivers/uwb/hwa-rc.c:hwarc_disconnect()/ +takes time of tearing everything down safely (or not...). + + + On the air: beacons and enumerating the radio neighborhood + +So assuming we have devices and we have agreed for a channel to connect +on (let's say 9), we put the new RC to beacon: + + * + + $ echo 9 0 > /sys/class/uwb_rc/uwb0/beacon + +Now it is visible. If there were other devices in the same radio channel +and beacon group (that's what the zero is for), the dongle's radio +control interface will send beacon notifications on its +notification/event endpoint (NEEP). The beacon notifications are part of +the event stream that is funneled into the API with +/drivers/uwb/neh.c:uwb_rc_neh_grok()/ and delivered to the UWBD, the UWB +daemon through a notification list. + +UWBD wakes up and scans the event list; finds a beacon and adds it to +the BEACON CACHE (/uwb_beca/). If he receives a number of beacons from +the same device, he considers it to be 'onair' and creates a new device +[/drivers/uwb/lc-dev.c:uwbd_dev_onair()/]. Similarly, when no beacons +are received in some time, the device is considered gone and wiped out +[uwbd calls periodically /uwb/beacon.c:uwb_beca_purge()/ that will purge +the beacon cache of dead devices]. + + + Device lists + +All UWB devices are kept in the list of the struct bus_type uwb_bus. + + + Bandwidth allocation + +The UWB stack maintains a local copy of DRP availability through +processing of incoming *DRP Availability Change* notifications. This +local copy is currently used to present the current bandwidth +availability to the user through the sysfs file +/sys/class/uwb_rc/uwbx/bw_avail. In the future the bandwidth +availability information will be used by the bandwidth reservation +routines. + +The bandwidth reservation routines are in progress and are thus not +present in the current release. When completed they will enable a user +to initiate DRP reservation requests through interaction with sysfs. DRP +reservation requests from remote UWB devices will also be handled. The +bandwidth management done by the UWB stack will include callbacks to the +higher layers will enable the higher layers to use the reservations upon +completion. [Note: The bandwidth reservation work is in progress and +subject to change.] + + + Wireless USB Host Controller drivers + +*WARNING* This section needs a lot of work! + +As explained above, there are three different types of HCs in the WUSB +world: HWA-HC, DWA-HC and WHCI-HC. + +HWA-HC and DWA-HC share that they are Wire-Adapters (USB or WUSB +connected controllers), and their transfer management system is almost +identical. So is their notification delivery system. + +HWA-HC and WHCI-HC share that they are both WUSB host controllers, so +they have to deal with WUSB device life cycle and maintenance, wireless +root-hub + +HWA exposes a Host Controller interface (HWA-HC 0xe0/02/02). This has +three endpoints (Notifications, Data Transfer In and Data Transfer +Out--known as NEP, DTI and DTO in the code). + +We reserve UWB bandwidth for our Wireless USB Cluster, create a Cluster +ID and tell the HC to use all that. Then we start it. This means the HC +starts sending MMCs. + + * + + The MMCs are blocks of data defined somewhere in the WUSB1.0 spec + that define a stream in the UWB channel time allocated for sending + WUSB IEs (host to device commands/notifications) and Device + Notifications (device initiated to host). Each host defines a + unique Wireless USB cluster through MMCs. Devices can connect to a + single cluster at the time. The IEs are Information Elements, and + among them are the bandwidth allocations that tell each device + when can they transmit or receive. + +Now it all depends on external stimuli. + +*New device connection* + +A new device pops up, it scans the radio looking for MMCs that give out +the existence of Wireless USB channels. Once one (or more) are found, +selects which one to connect to. Sends a /DN_Connect/ (device +notification connect) during the DNTS (Device Notification Time +Slot--announced in the MMCs + +HC picks the /DN_Connect/ out (nep module sends to notif.c for delivery +into /devconnect/). This process starts the authentication process for +the device. First we allocate a /fake port/ and assign an +unauthenticated address (128 to 255--what we really do is +0x80 | fake_port_idx). We fiddle with the fake port status and /khubd/ +sees a new connection, so he moves on to enable the fake port with a reset. + +So now we are in the reset path -- we know we have a non-yet enumerated +device with an unauthorized address; we ask user space to authenticate +(FIXME: not yet done, similar to bluetooth pairing), then we do the key +exchange (FIXME: not yet done) and issue a /set address 0/ to bring the +device to the default state. Device is authenticated. + +From here, the USB stack takes control through the usb_hcd ops. khubd +has seen the port status changes, as we have been toggling them. It will +start enumerating and doing transfers through usb_hcd->urb_enqueue() to +read descriptors and move our data. + +*Device life cycle and keep alives* + +Everytime there is a succesful transfer to/from a device, we update a +per-device activity timestamp. If not, every now and then we check and +if the activity timestamp gets old, we ping the device by sending it a +Keep Alive IE; it responds with a /DN_Alive/ pong during the DNTS (this +arrives to us as a notification through +devconnect.c:wusb_handle_dn_alive(). If a device times out, we +disconnect it from the system (cleaning up internal information and +toggling the bits in the fake hub port, which kicks khubd into removing +the rest of the stuff). + +This is done through devconnect:__wusb_check_devs(), which will scan the +device list looking for whom needs refreshing. + +If the device wants to disconnect, it will either die (ugly) or send a +/DN_Disconnect/ that will prompt a disconnection from the system. + +*Sending and receiving data* + +Data is sent and received through /Remote Pipes/ (rpipes). An rpipe is +/aimed/ at an endpoint in a WUSB device. This is the same for HWAs and +DWAs. + +Each HC has a number of rpipes and buffers that can be assigned to them; +when doing a data transfer (xfer), first the rpipe has to be aimed and +prepared (buffers assigned), then we can start queueing requests for +data in or out. + +Data buffers have to be segmented out before sending--so we send first a +header (segment request) and then if there is any data, a data buffer +immediately after to the DTI interface (yep, even the request). If our +buffer is bigger than the max segment size, then we just do multiple +requests. + +[This sucks, because doing USB scatter gatter in Linux is resource +intensive, if any...not that the current approach is not. It just has to +be cleaned up a lot :)]. + +If reading, we don't send data buffers, just the segment headers saying +we want to read segments. + +When the xfer is executed, we receive a notification that says data is +ready in the DTI endpoint (handled through +xfer.c:wa_handle_notif_xfer()). In there we read from the DTI endpoint a +descriptor that gives us the status of the transfer, its identification +(given when we issued it) and the segment number. If it was a data read, +we issue another URB to read into the destination buffer the chunk of +data coming out of the remote endpoint. Done, wait for the next guy. The +callbacks for the URBs issued from here are the ones that will declare +the xfer complete at some point and call it's callback. + +Seems simple, but the implementation is not trivial. + + * + + *WARNING* Old!! + +The main xfer descriptor, wa_xfer (equivalent to a URB) contains an +array of segments, tallys on segments and buffers and callback +information. Buried in there is a lot of URBs for executing the segments +and buffer transfers. + +For OUT xfers, there is an array of segments, one URB for each, another +one of buffer URB. When submitting, we submit URBs for segment request +1, buffer 1, segment 2, buffer 2...etc. Then we wait on the DTI for xfer +result data; when all the segments are complete, we call the callback to +finalize the transfer. + +For IN xfers, we only issue URBs for the segments we want to read and +then wait for the xfer result data. + +*URB mapping into xfers* + +This is done by hwahc_op_urb_[en|de]queue(). In enqueue() we aim an +rpipe to the endpoint where we have to transmit, create a transfer +context (wa_xfer) and submit it. When the xfer is done, our callback is +called and we assign the status bits and release the xfer resources. + +In dequeue() we are basically cancelling/aborting the transfer. We issue +a xfer abort request to the HC, cancell all the URBs we had submitted +and not yet done and when all that is done, the xfer callback will be +called--this will call the URB callback. + + + Glossary + +*DWA* -- Device Wire Adapter + +USB host, wired for downstream devices, upstream connects wirelessly +with Wireless USB. + +*EVENT* -- Response to a command on the NEEP + +*HWA* -- Host Wire Adapter / USB dongle for UWB and Wireless USB + +*NEH* -- Notification/Event Handle + +Handle/file descriptor for receiving notifications or events. The WA +code requires you to get one of this to listen for notifications or +events on the NEEP. + +*NEEP* -- Notification/Event EndPoint + +Stuff related to the management of the first endpoint of a HWA USB +dongle that is used to deliver an stream of events and notifications to +the host. + +*NOTIFICATION* -- Message coming in the NEEP as response to something. + +*RC* -- Radio Control + +Design-overview.txt-1.8 (last edited 2006-11-04 12:22:24 by +InakyPerezGonzalez) + |
