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diff --git a/en_US.ISO8859-1/books/arch-handbook/usb/chapter.sgml b/en_US.ISO8859-1/books/arch-handbook/usb/chapter.sgml deleted file mode 100644 index 9656256e31..0000000000 --- a/en_US.ISO8859-1/books/arch-handbook/usb/chapter.sgml +++ /dev/null @@ -1,623 +0,0 @@ -<!-- - The FreeBSD Documentation Project - - $FreeBSD$ ---> - -<chapter id="usb"> - <title>USB Devices</title> - - <para><emphasis>This chapter was written by &a.nhibma;. Modifications made for - the handbook by &a.murray;.</emphasis></para> - - <sect1> - <title>Introduction</title> - - <para>The Universal Serial Bus (USB) is a new way of attaching - devices to personal computers. The bus architecture features - two-way communication and has been developed as a response to - devices becoming smarter and requiring more interaction with the - host. USB support is included in all current PC chipsets and is - therefore available in all recently built PCs. Apple's - introduction of the USB-only iMac has been a major incentive for - hardware manufacturers to produce USB versions of their devices. - The future PC specifications specify that all legacy connectors - on PCs should be replaced by one or more USB connectors, - providing generic plug and play capabilities. Support for USB - hardware was available at a very early stage in NetBSD and was - developed by Lennart Augustsson for the NetBSD project. The - code has been ported to FreeBSD and we are currently maintaining - a shared code base. For the implementation of the USB subsystem - a number of features of USB are important.</para> - - <para><emphasis>Lennart Augustsson has done most of the implementation of - the USB support for the NetBSD project. Many thanks for this - incredible amount of work. Many thanks also to Ardy and Dirk for - their comments and proofreading of this paper.</emphasis></para> - - <itemizedlist> - - <listitem><para>Devices connect to ports on the computer - directly or on devices called hubs, forming a treelike device - structure.</para></listitem> - - <listitem><para>The devices can be connected and disconnected at - run time.</para></listitem> - - <listitem><para>Devices can suspend themselves and trigger - resumes of the host system</para></listitem> - - <listitem><para>As the devices can be powered from the bus, the - host software has to keep track of power budgets for each - hub.</para></listitem> - - <listitem><para>Different quality of service requirements by the - different device types together with the maximum of 126 - devices that can be connected to the same bus, require proper - scheduling of transfers on the shared bus to take full - advantage of the 12Mbps bandwidth available. (over 400Mbps - with USB 2.0)</para></listitem> - - <listitem><para>Devices are intelligent and contain easily - accessible information about themselves</para></listitem> - - </itemizedlist> - - <para>The development of drivers for the USB subsystem and devices - connected to it is supported by the specifications that have - been developed and will be developed. These specifications are - publicly available from the USB home pages. Apple has been very - strong in pushing for standards based drivers, by making drivers - for the generic classes available in their operating system - MacOS and discouraging the use of separate drivers for each new - device. This chapter tries to collate essential information for a - basic understanding of the present implementation of the USB - stack in FreeBSD/NetBSD. It is recommended however to read it - together with the relevant specifications mentioned in the - references below.</para> - - <sect2> - <title>Structure of the USB Stack</title> - - <para>The USB support in FreeBSD can be split into three - layers. The lowest layer contains the host controller driver, - providing a generic interface to the hardware and its scheduling - facilities. It supports initialisation of the hardware, - scheduling of transfers and handling of completed and/or failed - transfers. Each host controller driver implements a virtual hub - providing hardware independent access to the registers - controlling the root ports on the back of the machine.</para> - - <para>The middle layer handles the device connection and - disconnection, basic initialisation of the device, driver - selection, the communication channels (pipes) and does - resource management. This services layer also controls the - default pipes and the device requests transferred over - them.</para> - - <para>The top layer contains the individual drivers supporting - specific (classes of) devices. These drivers implement the - protocol that is used over the pipes other than the default - pipe. They also implement additional functionality to make the - device available to other parts of the kernel oruserland. They - use the USB driver interface (USBDI) exposed by the services - layer.</para> - </sect2> - </sect1> - - <sect1 id="usb-hc"> - <title>Host Controllers</title> - - <para>The host controller (HC) controls the transmission of - packets on the bus. Frames of 1 millisecond are used. At the - start of each frame the host controller generates a Start of - Frame (SOF) packet.</para> - - <para>The SOF packet is used to synchronise to the start of the - frame and to keep track of the frame number. Within each frame - packets are transferred, either from host to device (out) or - from device to host (in). Transfers are always initiated by the - host (polled transfers). Therefore there can only be one host - per USB bus. Each transfer of a packet has a status stage in - which the recipient of the data can return either ACK - (acknowledge reception), NAK (retry), STALL (error condition) or - nothing (garbled data stage, device not available or - disconnected). Section 8.5 of the <ulink - url="http://www.usb.org/developers/docs.html">USB - specification</ulink> explains the details of packets in more - detail. Four different types of transfers can occur on a USB - bus: control, bulk, interrupt and isochronous. The types of - transfers and their characteristics are described below (`Pipes' - subsection).</para> - - <para>Large transfers between the device on the USB bus and the - device driver are split up into multiple packets by the host - controller or the HC driver.</para> - - <para>Device requests (control transfers) to the default endpoints - are special. They consist of two or three phases: SETUP, DATA - (optional) and STATUS. The set-up packet is sent to the - device. If there is a data phase, the direction of the data - packet(s) is given in the set-up packet. The direction in the - status phase is the opposite of the direction during the data - phase, or IN if there was no data phase. The host controller - hardware also provides registers with the current status of the - root ports and the changes that have occurred since the last - reset of the status change register. Access to these registers - is provided through a virtualised hub as suggested in the USB - specification [ 2]. Thevirtual hub must comply with the hub - device class given in chapter 11 of that specification. It must - provide a default pipe through which device requests can be sent - to it. It returns the standard andhub class specific set of - descriptors. It should also provide an interrupt pipe that - reports changes happening at its ports. There are currently two - specifications for host controllers available: <ulink - url="http://developer.intel.com/design/USB/UHCI11D.htm">Universal - Host Controller Interface</ulink> (UHCI; Intel) and <ulink - url="http://www.compaq.com/productinfo/development/openhci.html">Open - Host Controller Interface</ulink> (OHCI; Compaq, Microsoft, - National Semiconductor). The UHCI specification has been - designed to reduce hardware complexity byrequiring the host - controller driver to supply a complete schedule of the transfers - for each frame. OHCI type controllers are much more independent - by providing a more abstract interface doing alot of work - themselves. </para> - - <sect2> - <title>UHCI</title> - - <para>The UHCI host controller maintains a framelist with 1024 - pointers to per frame data structures. It understands two - different data types: transfer descriptors (TD) and queue - heads (QH). Each TD represents a packet to be communicated to - or from a device endpoint. QHs are a means to groupTDs (and - QHs) together.</para> - - <para>Each transfer consists of one or more packets. The UHCI - driver splits large transfers into multiple packets. For every - transfer, apart from isochronous transfers, a QH is - allocated. For every type of transfer these QHs are collected - at a QH for that type. Isochronous transfers have to be - executed first because of the fixed latency requirement and - are directly referred to by the pointer in the framelist. The - last isochronous TD refers to the QH for interrupt transfers - for that frame. All QHs for interrupt transfers point at the - QH for control transfers, which in turn points at the QH for - bulk transfers. The following diagram gives a graphical - overview of this:</para> - - <para>This results in the following schedule being run in each - frame. After fetching the pointer for the current frame from - the framelist the controller first executes the TDs for all - the isochronous packets in that frame. The last of these TDs - refers to the QH for the interrupt transfers for - thatframe. The host controller will then descend from that QH - to the QHs for the individual interrupt transfers. After - finishing that queue, the QH for the interrupt transfers will - refer the controller to the QH for all control transfers. It - will execute all the subqueues scheduled there, followed by - all the transfers queued at the bulk QH. To facilitate the - handling of finished or failed transfers different types of - interrupts are generatedby the hardware at the end of each - frame. In the last TD for a transfer the Interrupt-On - Completion bit is set by the HC driver to flag an interrupt - when the transfer has completed. An error interrupt is flagged - if a TD reaches its maximum error count. If the short packet - detect bit is set in a TD and less than the set packet length - is transferred this interrupt is flagged to notify - the controller driver of the completed transfer. It is the host - controller driver's task to find out which transfer has - completed or produced an error. When called the interrupt - service routine will locate all the finished transfers and - call their callbacks.</para> - - <para>See for a more elaborate description the <ulink - url="http://developer.intel.com/design/USB/UHCI11D.htm">UHCI - specification.</ulink></para> - - </sect2> - - <sect2> - <title>OHCI</title> - - <para>Programming an OHCI host controller is much simpler. The - controller assumes that a set of endpoints is available, and - is aware of scheduling priorities and the ordering of the - types of transfers in a frame. The main data structure used by - the host controller is the endpoint descriptor (ED) to which - aqueue of transfer descriptors (TDs) is attached. The ED - contains the maximum packet size allowed for an endpoint and - the controller hardware does the splitting into packets. The - pointers to the data buffers are updated after each transfer - and when the start and end pointer are equal, the TD is - retired to the done-queue. The four types of endpoints have - their own queues. Control and bulk endpoints are queued each at - their own queue. Interrupt EDs are queued in a tree, with the - level in the tree defining the frequency at which they - run.</para> - - <para>framelist interruptisochronous control bulk</para> - - <para>The schedule being run by the host controller in each - frame looks as follows. The controller will first run the - non-periodic control and bulk queues, up to a time limit set - by the HC driver. Then the interrupt transfers for that frame - number are run, by using the lower five bits of the frame - number as an index into level 0 of the tree of interrupts - EDs. At the end of this tree the isochronous EDs are connected - and these are traversed subsequently. The isochronous TDs - contain the frame number of the first frame the transfer - should be run in. After all the periodic transfers have been - run, the control and bulk queues are traversed - again. Periodically the interrupt service routine is called to - process the done queue and call the callbacks for each - transfer and reschedule interrupt and isochronous - endpoints.</para> - - <para>See for a more elaborate description the <ulink - url="http://www.compaq.com/productinfo/development/openhci.html"> - OHCI specification</ulink>. Services layer The middle layer - provides access to the device in a controlled way and - maintains resources inuse by the different drivers and the - services layer. The layer takes care of the following - aspects:</para> - - <itemizedlist> - <listitem><para>The device configuration - information</para></listitem> - <listitem><para>The pipes to communicate with a - device</para></listitem> - <listitem><para>Probing and attaching and detaching form a - device.</para></listitem> - </itemizedlist> - - </sect2> - </sect1> - - <sect1 id="usb-dev"> - <title>USB Device Information</title> - - <sect2> - <title>Device configuration information</title> - - <para>Each device provides different levels of configuration - information. Each device has one or more configurations, of - which one is selected during probe/attach. A configuration - provides power and bandwidth requirements. Within each - configuration there can be multiple interfaces. A device - interface is a collection of endpoints. For example USB - speakers can have an interface for the audio data (Audio - Class) and an interface for the knobs, dials and buttons (HID - Class). All interfaces in a configuration areactive at the - same time and can be attached to by different drivers. Each - interface can have alternates, providing different quality of - service parameters. In for example cameras this is used to - provide different frame sizes and numbers of frames per - second.</para> - - <para>Within each interface 0 or more endpoints can be - specified. Endpoints are the unidirectional access points for - communicating with a device. They provide buffers to - temporarily store incoming or outgoing data from the - device. Each endpoint has a unique address within - a configuration, the endpoint's number plus its direction. The - default endpoint, endpoint 0, is not part of any interface and - available in all configurations. It is managed by the services - layer and not directly available to device drivers.</para> - - <para>Level 0 Level 1 Level 2 Slot 0</para> - <para>Slot 3 Slot 2 Slot 1</para> - <para>(Only 4 out of 32 slots shown)</para> - - <para>This hierarchical configuration information is described - in the device by a standard set of descriptors (see section 9.6 - of the USB specification [ 2]). They can be requested through - the Get Descriptor Request. The services layer caches these - descriptors to avoid unnecessary transferson the USB - bus. Access to the descriptors is provided through function - calls.</para> - - <itemizedlist> - <listitem><para>Device descriptors: General information about - the device, like Vendor, Product and Revision Id, supported - device class, subclass and protocol if applicable, maximum - packet size for the default endpoint, etc.</para></listitem> - - <listitem><para>Configuration descriptors: The number of - interfaces in this configuration, suspend and resume - functionality supported and power - requirements.</para></listitem> - - <listitem><para>Interface descriptors: interface class, - subclass and protocol if applicable, number of alternate - settings for the interface and the number of - endpoints.</para></listitem> - - <listitem><para>Endpoint descriptors: Endpoint address, - direction and type, maximum packet size supported and - polling frequency if type is interrupt endpoint. There is no - descriptor for thedefault endpoint (endpoint 0) and it is - never counted in an interface descriptor.</para></listitem> - - <listitem><para>String descriptors: In the other descriptors - string indices are supplied for some fields.These can be - used to retrieve descriptive strings, possibly in multiple - languages.</para></listitem> - - </itemizedlist> - - <para>Class specifications can add their own descriptor types - that are available through the GetDescriptor Request.</para> - - <para>Pipes Communication to end points on a device flows - through so-called pipes. Drivers submit transfers to endpoints - to a pipe and provide a callback to be called on completion or - failure of the transfer (asynchronous transfers) or wait for - completion (synchronous transfer). Transfers to an endpoint - are serialised in the pipe. A transfer can either complete, - fail or time-out (if a time-out has been set). There are two - types of time-outs for transfers. Time-outs can happen due to - time-out on the USBbus (milliseconds). These time-outs are - seen as failures and can be due to disconnection of the - device. A second form of time-out is implemented in software - and is triggered when a transfer does not complete within a - specified amount of time (seconds). These are caused by a - device acknowledging negatively (NAK) the transferred - packets. The cause for this is the device not being ready to - receive data, buffer under- or overrun or protocol - errors.</para> - - <para>If a transfer over a pipe is larger than the maximum - packet size specified in the associated endpoint descriptor, - the host controller (OHCI) or the HC driver (UHCI) will split - the transfer into packets of maximum packet size, with the - last packet possibly smaller than the maximum - packetsize.</para> - - <para>Sometimes it is not a problem for a device to return less - data than requested. For example abulk-in-transfer to a modem - might request 200 bytes of data, but the modem has only 5 - bytes available at that time. The driver can set the short - packet (SPD) flag. It allows the host controller to accept a - packet even if the amount of data transferred is less than - requested. This flag is only valid for in-transfers, as the - amount of data to be sent to a device is always known - beforehand. If an unrecoverable error occurs in a device - during a transfer the pipe is stalled. Before any more data is - accepted or sent the driver needs to resolve the cause of the - stall and clear the endpoint stall condition through send the - clear endpoint halt device request over the default - pipe. The default endpoint should never stall.</para> - - <para>There are four different types of endpoints and - corresponding pipes: - Control pipe / default pipe: There is - one control pipe per device, connected to the default endpoint - (endpoint 0). The pipe carries the device requests and - associated data. The difference between transfers over the - default pipe and other pipes is that the protocol for - thetransfers is described in the USB specification [ 2]. These - requests are used to reset and configure the device. A basic - set of commands that must be supported by each device is - provided in chapter 9 of the USB specification [ 2]. The - commands supported on this pipe canbe extended by a device - class specification to support additional - functionality.</para> - - <itemizedlist> - <listitem><para>Bulk pipe: This is the USB equivalent to a raw - transmission medium.</para></listitem> - <listitem><para>Interrupt pipe: The host sends a request for - data to the device and if the device has nothing to send, it - will NAK the data packet. Interrupt transfers are scheduled - at a frequency specifiedwhen creating the - pipe.</para></listitem> - - <listitem><para>Isochronous pipe: These pipes are intended for - isochronous data, for example video oraudio streams, with - fixed latency, but no guaranteed delivery. Some support for - pipes of this type is available in the current - implementation. Packets in control, bulk and interrupt - transfers are retried if an error occurs during transmission - or the device acknowledges the packet negatively (NAK) due to - for example lack of buffer space to store the incoming - data. Isochronous packets are however not retried in case of - failed delivery or NAK of a packet as this might violate the - timing constraints.</para></listitem> - </itemizedlist> - - <para>The availability of the necessary bandwidth is calculated - during the creation of the pipe. Transfersare scheduled within - frames of 1 millisecond. The bandwidth allocation within a - frame is prescribed by the USB specification, section 5.6 [ - 2]. Isochronous and interrupt transfers areallowed to consume - up to 90% of the bandwidth within a frame. Packets for control - and bulk transfers are scheduled after all isochronous and - interrupt packets and will consume all the remaining - bandwidth.</para> - - <para>More information on scheduling of transfers and bandwidth - reclamation can be found in chapter 5of the USB specification - [ 2], section 1.3 of the UHCI specification [ 3] and section - 3.4.2 of the OHCI specification [4].</para> - - </sect2> - </sect1> - - <sect1 id="usb-devprobe"> - <title>Device probe and attach</title> - - <para>After the notification by the hub that a new device has been - connected, the service layer switcheson the port, providing the - device with 100 mA of current. At this point the device is in - its default state and listening to device address 0. The - services layer will proceed to retrieve the various descriptors - through the default pipe. After that it will send a Set Address - request to move the device away from the default device address - (address 0). Multiple device drivers might be able to support - the device. For example a modem driver might beable to support - an ISDN TA through the AT compatibility interface. A driver for - that specific model of the ISDN adapter might however be able to - provide much better support for this device. To support this - flexibility, the probes return priorities indicating their level - of support. Support for a specific revision of a product ranks - the highest and the generic driver the lowest priority. It might - also be that multiple drivers could attach to one device if - there are multiple interfaceswithin one configuration. Each - driver only needs to support a subset of the interfaces.</para> - - <para>The probing for a driver for a newly attached device checks - first for device specific drivers. If notfound, the probe code - iterates over all supported configurations until a driver - attaches in a configuration. To support devices with multiple - drivers on different interfaces, the probe iteratesover all - interfaces in a configuration that have not yet been claimed by - a driver. Configurations that exceed the power budget for the - hub are ignored. During attach the driver should initialise the - device to its proper state, but not reset it, as this will make - the device disconnect itself from the bus and restart the - probing process for it. To avoid consuming unnecessary bandwidth - should not claim the interrupt pipe at attach time, but - should postpone allocating the pipe until the file is opened and - the data is actually used. When the file is closed the pipe - should be closed again, eventhough the device might still be - attached.</para> - - <sect2> - <title>Device disconnect and detach</title> - - <para>A device driver should expect to receive errors during any - transaction with the device. The designof USB supports and - encourages the disconnection of devices at any point in - time. Drivers should make sure that they do the right thing - when the device disappears.</para> - - <para>Furthermore a device that has been disconnected and - reconnected will not be reattached at the same device - instance. This might change in the future when more devices - support serial numbers (see the device descriptor) or other - means of defining an identity for a device have been - developed.</para> - - <para>The disconnection of a device is signalled by a hub in the - interrupt packet delivered to the hub driver. The status - change information indicates which port has seen a connection - change. The device detach method for all device drivers for - the device connected on that port are called and the structures - cleaned up. If the port status indicates that in the mean time - a device has been connected to that port, the procedure for - probing and attaching the device will be started. A device - reset will produce a disconnect-connect sequence on the hub - and will be handled as described above.</para> - - </sect2> - </sect1> - - <sect1 id="usb-protocol"> - <title>USB Drivers Protocol Information</title> - - <para>The protocol used over pipes other than the default pipe is - undefined by the USB specification. Information on this can be - found from various sources. The most accurate source is the - developer's section on the USB home pages [ 1]. From these pages - a growing number of deviceclass specifications are - available. These specifications specify what a compliant device - should look like from a driver perspective, basic functionality - it needs to provide and the protocol that is to be used over the - communication channels. The USB specification [ 2] includes the - description of the Hub Class. A class specification for Human - Interface Devices (HID) has been created to cater for keyboards, - tablets, bar-code readers, buttons, knobs, switches, etc. A - third example is the class specification for mass storage - devices. For a full list of device classes see the developers - sectionon the USB home pages [ 1].</para> - - <para>For many devices the protocol information has not yet been - published however. Information on the protocol being used might - be available from the company making the device. Some companies - will require you to sign a Non -Disclosure Agreement (NDA) - before giving you the specifications. This in most cases - precludes making the driver open source.</para> - - <para>Another good source of information is the Linux driver - sources, as a number of companies have started to provide drivers - for Linux for their devices. It is always a good idea to contact - the authors of those drivers for their source of - information.</para> - - <para>Example: Human Interface Devices The specification for the - Human Interface Devices like keyboards, mice, tablets, buttons, - dials,etc. is referred to in other device class specifications - and is used in many devices.</para> - - <para>For example audio speakers provide endpoints to the digital - to analogue converters and possibly an extra pipe for a - microphone. They also provide a HID endpoint in a separate - interface for the buttons and dials on the front of the - device. The same is true for the monitor control class. It is - straightforward to build support for these interfaces through - the available kernel and userland libraries together with the - HID class driver or the generic driver. Another device that - serves as an example for interfaces within one configuration - driven by different device drivers is a cheap keyboard with - built-in legacy mouse port. To avoid having the cost of - including the hardware for a USB hub in the device, - manufacturers combined the mouse data received from the PS/2 port - on the back of the keyboard and the keypresses from the keyboard - into two separate interfaces in the same configuration. The - mouse and keyboard drivers each attach to the appropriate - interface and allocate the pipes to the two independent - endpoints.</para> - - <para>Example: Firmware download Many devices that have been - developed are based on a general purpose processor with - anadditional USB core added to it. Because the development of - drivers and firmware for USB devices is still very new, many - devices require the downloading of the firmware after they - have been connected.</para> - - <para>The procedure followed is straightforward. The device - identifies itself through a vendor and product Id. The first - driver probes and attaches to it and downloads the firmware into - it. After that the device soft resets itself and the driver is - detached. After a short pause the devicere announces its presence - on the bus. The device will have changed its - vendor/product/revision Id to reflect the fact that it has been - supplied with firmware and as a consequence a second driver will - probe it and attach to it.</para> - - <para>An example of these types of devices is the ActiveWire I/O - board, based on the EZ-USB chip. For this chip a generic firmware - downloader is available. The firmware downloaded into the - ActiveWire board changes the revision Id. It will then perform a - soft reset of the USB part of the EZ-USB chip to disconnect from - the USB bus and again reconnect.</para> - - <para>Example: Mass Storage Devices Support for mass storage - devices is mainly built around existing protocols. The Iomega - USB Zipdrive is based on the SCSI version of their drive. The - SCSI commands and status messages are wrapped in blocks and - transferred over the bulk pipes to and from the device, - emulating a SCSI controller over the USB wire. ATAPI and UFI - commands are supported in a similar fashion.</para> - - <para>The Mass Storage Specification supports 2 different types of - wrapping of the command block.The initial attempt was based on - sending the command and status through the default pipe and - using bulk transfers for the data to be moved between the host - and the device. Based on experience a second approach was - designed that was based on wrapping the command and status - blocks and sending them over the bulk out and in endpoint. The - specification specifies exactly what has to happen when and what - has to be done in case an error condition is encountered. The - biggest challenge when writing drivers for these devices is to - fit USB based protocol into theexisting support for mass storage - devices. CAM provides hooks to do this in a fairly straight - forward way. ATAPI is less simple as historically the IDE - interface has never had many different appearances.</para> - - <para>The support for the USB floppy from Y-E Data is again less - straightforward as a new command set has been designed.</para> - - </sect1> - -</chapter>
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