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.
  
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     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
  
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     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 assignment, 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
  disappear.
  
  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*
  
  Every time there is a successful 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 its 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, cancel 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)