USB. The Universal Serial Bus. Most of the material is taken from Jan Axelsson: USB Complete, third edition Lakeview Research ISBN:

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1 USB The Universal Serial Bus Most of the material is taken from Jan Axelsson: USB Complete, third edition Lakeview Research ISBN:

2 Usability, easy to use Demands to forfill Speed, fast enough not to hinder traffic Reliability, low error rate, retry when errors occur Versatility, suitable for many types of peripherals Cheap, specially in the end Low power, batteries, bus power Support from common OS: Windows, Linux, Mac OS, Android Abilities Use the same interface for many kinds of peripherals using the same connector Get automatic configuration. When the OS detects a new it will load the appropriate driver Easy connection. The connector is small and can not be inserted the wrong way Hot plug, the s can be connected whenever we want. No restarting of the system Starts communication without user settings. No address to set. No interrupts to allocate In many cases bus powered 2

Interface comparison USB versus FireWire In FireWire the communicating nodes can be any nodes on the bus USB communication is always between the host and a

3 Interface comparison USB versus FireWire In FireWire the communicating nodes can be any nodes on the bus USB communication is always between the host and a FireWire has broadcasting capabilities Higher demands on peripheral nodes in FireWire FireWire nodes are more complicated, as a result also more expensive 3

4 USB versus Ethernet Ethernet can use long cables Ethernet has broadcasting capabilities Ethernet has support for Internet protocols Ethernet has a more complicated interface than USB USB is more flexible with four transfer types and three speed grades, not counting USB3 USB disadvantages Too slow for demanding applications Does not apply to version 3.0 Short distance, up to 5 meters Could be extended using an active repeater The host handles all communication, s can not talk to each other No broadcasting capability All communications goes through the OS and a driver, you can not interact directly with the port 4

5 The USB bus Root hub in host (PC) Additional external hubs Peripheal Root hub Peripheal Tired star Peripheal Hub Peripheal Hub Peripheal Peripheal Peripheal Hubs connect to s The USB bus cont. The host is in charge of the bus Only one at a time can communicate with the host The host detects s connected to the bus The host controller hardware and drivers do most of the handling of the bus The applications use standard d OS calls to send and retrieve data The applications does not have to be aware of USB details or even that the bus uses USB 5

6 Speed grades Low-speed, 1.5 Mbits/sec USB 1.x Full-speed, 12 Mbits/sec High-speed, 480 Mbits/sec USB 2.0 High speed 2.0 hub Highspeed Low speed Full speed USB network High speed Highspeed High speed 2.0 host and root hub Full-speed Low/full speed Low speed Full speed Lowspeed Full speed Full speed 1.x hub High- speed Lowspeed Lowspeed Low speed Full-speed Full-speed 6

7 Frames Low- and full-speed transfers use 1 millisecond long frames, within which each transfer is allocated space At high-speed every frame is divided into microsecond long microframes Each frame or microframe starts with a Start-of-Frame timing reference Start of Frame Device 1, endpoin Device 1, endpoin Device 5, endpoin Device 5, endpoin Device 5, endpoin unused Start of Frame Device 1, endpoin Device 2, endpoin Device 5, endpoin Device 5, endpoin unused Start of Frame Device 1, endpoin Device 2, endpoin Device 2, endpoin unused t 2 t 2 t 3 t 3 t 3 t 2 t 0 t 3 t 3 t 2 t 0 t 0 Endpoints and pipes All transactions on the bus are between endpoints Endpoints are connected through pipes All pipes except control pipes are one-directional All endpoints except control endpoints are one-directional IN endpoints pass information to the host OUT endpoints pass information from the host 7

8 Endpoints and pipes cont. Control endpoints are used for control and status information but can also transfer data Other endpoints transfer data Transfer types Control transfer Used by the host to read information about a, set the s address and configuration, can send vendor specific information, can transfer small amounts of data. Must be supported by all USB s Bulk transfer Used when the transfer rate is not of the highest priority but the data size may be large. Printers, scanners external drives 8

The only way for low-speed s to communicate, besides control transfers.

9 Transfer types cont. Interrupt transfer Used by s that must receive attention periodically. The only way for low-speed s to communicate, besides control transfers. Used for mice and keyboards Isochronous transfer Have guaranteed delivery time but no error correction. Typically for audio and video in real time Transfer types cont. 9

10 Control transfer Carry requests are used by the host to learn about and configure s All USB s must support control transfers Three stages Setup stage The host sends information about the request Data stage Data is send throughh IN or OUT transactions. ti The stage is optional since not all requests carry data Status stage Reports success or failure of previous stages Control transfer cont. Maximum size of data packet Low-speed 8bytes Full-speed 8, 16, 32 or 64 bytes High-speed 64 bytes Control transfers can be used to transfer other kinds of information but the overhead is quit large The only way for low-speed s to transfer information, except through interrupt transfer The response time for control transfers can be quit long 10

11 Bulk transfer Transfers when the time isn t critical Can transfer large amounts of data without t filling the bus since it defers other types of transfer and waits for available bus time Fast on an idle bus Only full- and high-speed transfers. Data to printers, from scanners, to and from external drives Uses error detection and re-sending Interrupt transfer Useful when the data has to transfer within a specific amount of time Keyboards, mice, game controllers We don t want a delay between pressing a key on the keyboard and the response on the screen The host polls the for data like any other. The transfer type guarantees that the host requests or sends data with minimal delay. There is no guaranteed transfer rate. All three speeds allowed 11

12 Interrupt transfer cont. The host may begin each transaction at any time up to the maximum latency since the last transaction began. Interrupt transfers doesn t guarantee a precise rate of delivery. Can be very fast at high-speed, Megabytes/sec. The same error-checking as bulk transfer Isochronous transfer For streaming real-time transfers when data must arrive at a constant rate or by a specific time. Transfer of voice and music played in real-time No error-checking. No re-transmission of erroneous data For data transfered first and played back later bulk transfer might be a better choice Data doesn t have to arrive at a constant rate as long as the data is available when needed, that is the transmission can take place in bursts Before setting up a isochronous transfer the host determines if the requested bandwidth is available 12

13 Enumeration Before applications can communicate with a the host needs to learn about the and assign a driver. This is done in the enumeration process The process includes assigning an address to the, reading descriptors from the, assigning and loading a driver and selecting a configuration The enumeration process is invisible to the user except maybe for a message that a new has been detected. On first use the user may be prompted for the location of driver files Enumeration sequence 1. The user attaches a new or the system power-up 2. The hub detects the 3. The host learns of the new 4. The hub detects whether the is full- or low-speed. A high-speed will start-up as full-speed 5. The hub resets the 6. The hub learns if a full-speed supports high-speed 7. The hub establishes a signal path between the and the bus. Communication use the defauilt address 0x00 13

14 Enumeration sequence cont. 8. The host requests the maximum packet size from the default pipe 9. The host assigns an unique address to the 10. The host learns the capabilities of the 11. The host assigns and loads a driver 12. The host s driver selects a configuration Descriptors USB descriptors are data structures that enable the host to learn about a. During enumeration the host requests the descriptors from the. There are four basic descriptor types 14

15 Device descriptor Descriptors cont. Basic information about the whole. Specifies the number of configurations the supports Configuration descriptors Information about the s use of power and the number of interfaces supported by the configuration Interface descriptors Specifies the endpoint descriptors Endpoint descriptors Specifies how the endpoint transfers data Device classes A class gathers s that have much in common and perform simular functions The s or interfaces in a class share many attributes and provide or request simular services The class has a common class driver The specification defines the number and type of required and optional endpoints. It may also define or name formats for data to be transferred Vendors can add filter drivers to support added features 15

Device classes with approved class specifications The audio class For s that send or receive audio data, which may include encoded voice, music or other sounds Often part of s that also support

16 Device classes with approved class specifications The audio class For s that send or receive audio data, which may include encoded voice, music or other sounds Often part of s that also support video, storage or other functions Uses isochronous transfer for audio streams or bulk transfer for data using the MIDI protocol. The AudioControl interface access controls such as volume, mute, bass and treble Zero or more AudioStreaming interfaces transfers audio using isochronous transfer Zero or more MIDIStreaming interfaces transfers MIDI data using bulk transfer 16

17 Musical Instrument Digital Interface MIDI Standard for controlling synthesizers, sound cards and other electronic s that generate music or other sounds The data includes values for pitch, length, volume and other characteristics The interface does not transfer sound The interface uses asynchronous transfer at kbits/sec A USB interface that carries MIDI data does not use the asynchronous interface but use bulk transfer The chip/smart card interface class Smart cards are used in phones, gift cards, keyless entry, storing medical data, storing photographs, h enabling of satellite TV receivers and other applications that require storing small or moderate quantities of data with easy and portable access Each card contains memory and often a CPU Many cards allow updating of the contents using a connector or an embedded antenna 17

18 The chip/smart card interface class cont. To access the card you connect it to a Chip Card Interface Device, CCID (smart card reader) Some of these CCIDs have USB interfaces and these use this class The CCID use bulk transfer to exchange data between the host and the The CCID use interrupt transfer to report errors and the insertion or removal of a card The communication class, CDC The class have two broad types: Telephones including analog telephones and modems, ISDN terminal adapters and digital phones Medium-speed networking s including ADSL modems, cable modems and 10BASE-T Ethernet adapters and hubs Two subclasses: The Wireless Mobile Communications subclass including terminal equipment for wireless s The Ethernet Emulation Model subclass including s that send and receive Ethernet frames 18

19 The communication class, CDC cont. The Remote Network Driver Interface Specification (Remote NDIS) defines a protocol for using USB and other buses to configure network interfaces and to send and receive Ethernet data CDC supports three basic models for communications: The Plain Old Telephone Service (POTS) model for communicating via ordinary phone lines The Integrated Services Digital Network (ISDN) model for communications via phone lines using ISDN The Networking model for communications via Ethernet or Asynchronous Transfer Mode (ATM) The content security class The class defines a way for owners to control access to files, music, video and other data transmitted on the bus. The control can use either of two defined Content Security Methods (CSM) Basic Authorization (CSM-1) only enables a host to request an ID from the Digital Content Protection (DTCP, CSM-2) can be used to specify whether copying is allowed, identify authorized users and specify an encryption method The class defines a method for activating and deactivating a content security method and for associating a method to a channel 19

20 The firmware upgrade class, DFU The class defines a protocol to enable a host to send firmware enhancements and patches to a The must have two sets of descriptors: run-time and DFU-mode descriptors DFU communications only usethe control endpoint The human interface class, HID Human interfaces (HID) are s that the host uses to react to human input such as keypresses and mouse movement The host must react quickly so the user doesn t notice a delay between input and response Low-speed is fast enough to avoid notable delays All data travels in reports with tags that tell the host or how to use the data HIDs communicate by exchanging reports using control and interrupt transfers 20

21 The Infrared Data Association (IrDA) bridge class The IrDA interface defines hardware requirements and protocols for exchanging data over short distances using infrared light A USB IrDA bridge converts between USB and IrDA data The IrDA link uses the Infrared Access Protocol (IrLAP) which defines the format of the IrDA frames The USB IrDA bridge uses bulk transfers to exchange data with the host The mass storage class For s that transfers files in one or both directions, typically floppy, hard, CD, DVD and flash-memory drives Under Windows the s of this class appears as drives in My Computer and the file system The s use bulk transfers to exchange data. Control transfers can send class-specific requests. To exchange other information the may use bulk or control/bulk/interrupt transfer A mass storage can use just about any full- or high speed controller chip 21

22 The printer class For s that convert received data into text and/or images on paper or other media Most printers understand one or more page description languages (PDL) The USB Printing Device specification is for printers of all types Transfers use bulk transfer A printer class can use just about any full- or high speed controller chip The still image capture class For s like cameras that capture still images (not video) and scanners To transfer image files from a camera the mass storage class is another option The s use bulk transfer to transport both image and non-image data. An interrupt transfer is required to transfer event data The information travels in structures called containers. There are four types: Command Block, Data Block, Response Block and Event Block A still image capture class can use just about any full- or high speed controller chip 22

23 The test and measurement class Suited for instrumentation s where the data doesn t need guaranteed timingi The may be stand alone or a card in a computer The USB488 subclass defines protocols to communicate using IEEE488 s (GPIB) data format and commands The class uses bulk transfers. The USB488 subclass requires an interrupt transfer as well. This is optional for other s in the class The video class Supports digital camcorders, webcameras and other s that send, receive or manipulate transient or moving images Transfering high-quality video requires high bandwidth so high-speed hosts are in most cases required Every video function must have a VideoControl interface Every video function must have a VideoControl interface. Most functions also have one or more VideoStreaming interfaces 23

24 Host communication An application that wants to access a USB peripheral must communicate with a driver Under Windows the driver is layered: The application communicates with a client driver using API functions The client driver communicate with USB drivers consisting of a host controller and a hub driver The host controller manages tasks common to all host controllers. The hub driver manages communications with the system s hub. Host controllers For low- and full-speed communication: The Open Host Controller Interface (OHCI) that places a lot of the burdon on hardware The Universal Host Controller Interface (UHCI) that places a lot of the burdon on software For high-speedh communication: The Enhanced Host Controller Interface (EHCI) 24

25 Matching a driver to a Windows stores information about installed hardware and software in the registry For USB s some of the information comes from the during enumeration Other information comes from the Device Setup Information File (INF file). A file linked to the driver that the host assigns to the Hubs Every USB peripheral must connect to a hub. An intelligent that provides attachment points for s and manages each s connection to the bus Devices that plug into the PC connect to the root hub Devices that plug into external hubs plug into a hub downstream from the host The hub manages the s connection by helping new s to connect and start running and by blocking out missbehaving s 25

26 External hubs The hub has one upstream connection connecting either directly to the root hub or to another hub upstream The hub has one or more downstream connections to connect s or other hubs Hubs can use version 1.x or version 2.0 of the USB standard Every hub contains a hub repeater and a hub controller The hub repeater passes information from the host to downstream s and from the s to the host The hub controller manages the communications between the host and the hub repeater 1.x hubs A1.xhub can only handle low- and full-speed communication The hub repeater repeats all low- and full-speed packets to all full-speed downstream ports The repeater doesn t translate, examine the contents of or process the traffic from the full-speed source in any way it just regenerates the edges of the signal Only low-speed packets are repeated to low-speed ports 26

27 2.0 hubs A20h 2.0 hub uses high-speedh upstream when the hub connects to a high-stream bus segment In this case all communications upstream uses high-speed even if the traffic is to or from a fullor low-speed To do this the hub has to translate between bus speeds High speed 2.0 hub Highspeed Low speed Full speed USB network High speed Highspeed High speed 2.0 host and root hub Full-speed Low/full speed Low speed Full speed Lowspeed Full speed Full speed 1.x hub High- speed Lowspeed Lowspeed Low speed Full-speed Full-speed 27

28 Voltage and power Devices can be powered through the USB connection or use their own power supply. The USB bus can supply a voltage of 5 volts. There is also a ground connection. There is a limit to the available current. There are two classes of s: Low power, up to 100 Milliamperes, laptops High power, up to 500 Milliamperes, tabletop PC s self-powered hubs Voltage and power cont. Low power s can be bus powered from any host or hub. High power s can use bus power when attached to a self-powered hub or any host except some batteri powered hosts (laptops). Some s, like digital cameras, needs to function when they are not attached so they need their own power supply. Some of these can charge their batteries when attached to the bus. 28

29 Hubs and power A bus powered hub can draw 500 Milliamperes from the host. The hub uses some of this leaving less than 500 Milliamperes to supply to all attached s. A self powered hub doesn t have this limitation. It can supply 500 Milliamperes to all attached s. A hub should be able to detect an over-current condition, limit the current and inform the host. Bus signals The USB bus is a balanced bus Parameter Low/full speed (V) High speed (V) Vout,low min Vout,low max Vout,high min Vout,high max Vin,low max 0.8 Limited by eyepattern Vin,high min 2.0 in USB specification 29

30 USB wires There are four conductors in a USB cable: Vbus +5 volts Gnd, ground reference D+, positive in differential signal pair D-, negative in differential signal pair USB connectors USB 2.0 defines the Series-A plug for the upstream end of the cable and the Series-B plug for the downstream end. Two smaller versions, mini-b and micro-b has been defined for applications where the other connectors are too bulky. 30

31 USB connectors cont. Micro-B Mini-B Series-B Series-A extension Series-A USB On-the-Go Makes it possible for a to function as a limited host. In this way it is for example possible for a digital camera that normally functions as a to act as a host when it connects to a printer without having to connect to a host computer. 31

32 Wireless USB Should behave as USB but without the wire Keep the software infrastructure of USB intact Preserve the USB model of a smart host and a simple Without wires batteries are usual so power efficency is important Keep the security of USB A new USB class, the wire adapter class allows existing PCs to upgrade to wireless support and allows wired s to have wireless connection to PC Wireless USB cont. A hub and spoke model The host is the hub at the center Each sits at the end of a spoke Each spoke is a point-to-point connection between the host and the A host can support up to 127 s Without wires there is no need for port expansion 32

33 Wireless USB cont. Wire adapters that connect through wire to a PC and gives it USB capability are called Host Wire Adapters Wire adapters that connect wirelessly to the PC are called Device Wire Adapters Each adapter creates a new USB system with one host talking to one or more s Wireless s are divided into classes just as wired s Wireless USB cont. The physical layer follows the Multiband OFDM Alliance UWB PTY specification GHz with a 7.5 MHz bandwidth Wireless s must support data rates of 53.3, 106,7 and 200 Mb/s 80, 160, 320, 400 and 480 Mb/s are optional Logically a polled, TDMA based protocol similar to wired USB is used Each transfer consists of token, data and handshake Devices attach to a host by sending a message to the host and then authentification takes place 33

34 The future of USB The USB 3.0 (SuperSpeed USB) specification has been presented Speed up to 4.8 Gbit/s Backward compatable with USB 2.0 New wiring with four conductors enables simultaneous bi-directional traffic The connectors have som extra pins but can still take the old connectors. The extra pins are used as two twisted pairs for the SuperSpeed communication and an extra ground Current limit raised to 900 Milliamperes Maximal wire length 3 meters 34

David Harrison, Design Engineer for Model Sounds Inc.

David Harrison, Design Engineer for Model Sounds Inc. 1 History -1 In 1994 an alliance of four industry partners (Compaq, Intel, Microsoft and NEC) started to specify the Universal Serial Bus (USB). The