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+
+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)
+