Advance of usb
- 2. Agenda USB Specifications USB Basics Components Onion introduction Signaling Packets Transfers Requests Operating System Interface USB Resources
- 3. USB in 1996: Initially introduced as an additional connector for new applications. USB PC Connectivity Vision Universal Serial Bus Keyboard Mouse Serial Port Parallel Port SCSI Port Sound/Game Ports Graphics Port LAN Modem Graphics Port LAN USB Future: The PC evolves into a simpler, easier to use appliance. USB USB USB Telephony, Modem, Keyboard, Mouse,Game ports, Serial ports Device,Digital Audio, Printer, Scanner
- 4. USB Specifications USB 1.0 – The original spec, superseded quickly by USB 1.1 USB 1.1 – Minor enhancements to the USB 1.0 spec, supported Low and Full speed devices USB 2.0 – The Current Standard, added “high speed’ to USB 1.1 USB OTG – USB On-the-Go, a supplement to the USB 2.0 spec that added a form of device to device communications.
- 5. USB Founding Companies USB 1.0 USB 2.0 Compaq Compaq Intel Intel Microsoft Microsoft NEC NEC IBM Lucent DEC HP Northern Telecom Philips
- 6. USB 2.0 in a Nutshell Runs 40X faster than USB 1.1 Low speed: 1.5Mb/s Full speed: 12Mb/s High speed: 480Mb/s Fully supports existing USB devices Forward compatible—plug existing 1.1 devices into new 2.0 hosts Backward compatible—plug new 2.0 devices into existing 1.1 hosts Uses the same cables as USB 1.1
- 7. Hardware Overview... Topology Tiered Star (Distributes Connectivity Points) 127 logical connections (upto 5 meters per segment) Upto 6 tiers ... Universal Serial Bus USB Monitor SpeakerPen Mouse Kbd Mic Phone PC HUBHUB HOST/HUB
- 8. USB On-the-Go (USB OTG) Connect two ‘peripherals’ together PC is not required (but still supported) Allow peripherals to wake up hosts Allow two devices to exchange the host role New OTG devices can tap into the existing 900 million USB devices
- 9. USB OTG Example Applications Source: Beeman: www.usbonthego.com Exchange pictures Upload pictures to web Print pictures Camera Cell Phone Printer Camera Exchange songsMP3 playerMP3 player Exchange Contact info Print call info Upload pictures to web Cell Phone Printer Camera Cell Phone Synchronize phone list, meetings Upload pictures Download songs Cell Phone Camera MP3 player PC ApplicationsPeripheralHost
- 10. USB OTG Details Defines a new connector and cable “Mini AB” receptacle Mini-A to Mini-B cable Cable establishes the default host A-Device is the default host Dual-role USB devices: Are sometimes a peripheral, sometimes a host Must use the new AB connector Provide limited host capability Targeted peripheral list Operate at full speed (high speed optional)
- 11. USB Basics
- 12. USB Basics USB is a Master/Slave Polled Bus (PC is the “Master”, Devices are the “Slaves”) USB has a “tiered star” architecture that can USB can support up to 127 devices 7-bit address = 128 – root hub – reserved addr 0 for enumeration USB is “Hot Pluggable” USB connections can provide both data and power to the devices
- 13. USB is not Simple Outside, it is simple The “rich user experience” requires some inner complexity Even though it replaces serial and parallel ports, it’s not a drop-in replacement It’s electrically simple, but a whole protocol layer is added
- 14. USB Projects Can Require a Significant Code Development Effort Device side USB houskeeping firmware Application firmware Host side Driver (maybe) Application software
- 15. USB Components
- 16. Components of USB Systems USB Host Controllers USB Hubs USB Cables USB Peripheral Devices
- 17. USB Host Controllers Reside in PC on motherboard or add-in card Are the “master” device on the USB bus Host Controller has integral “Root Hub” Host Controller Interfaces: Universal Host Controller Interface (UHCI) Open Host Controller Interface (OHCI) Enhanced Host Controller Interface (EHCI)
- 18. USB Cables Transport both Data and Power Four wires: Vbus, GND, D+, D– Cables are 5 meters MAX Two connector types, “A” and “B” Prevents illegal topologies “A” connectors are the ones that goes to the PC or Hub, “B” connectors goes to the device) (OTG adds Miny A and Mini B connectors) Cables can be either “captive” (like mice) or detachable Cables can be unshielded (Low speed devices) or shielded (Full Speed and High Speed devices) USB extension cables are ILLEGAL
- 19. USB Hubs A hub provides additional connection points (ports) for devices Hubs can be: Self-Powered (<= 500ma to each device) Bus-Powered (<= 100mA to each device) Hubs contain most of the “magic” and differences between USB 1.1 and USB 2.0
- 20. USB Devices Devices can be: Self-Powered External Power Source (i.e. wall wart) Batteries Bus-Powered Low Power Bus Powered (<= 100mA) High Power Bus Powered >100mA, <=500mA) Devices are “self describing” Devices return data (USB descriptors) to host to indicate its capabilities, configurations, and how the device is able to communicate
- 21. Compound and Composite Devices Composite Device Multiple interfaces, independently controlled Each interface can have a different driver Compound Device Collection of separate functions, each with a USB address, connected to an internal hub Example: Keyboard & Trackball in same package
- 22. USB is a Polled BUS The Host (PC) initiates all transfers Devices respond to host requests Direction: OUT is host-to-device Direction: IN is device-to-host USB is NOT peer-to-peer (not even in USB OTG)
- 23. USB Topology PC USB USB “Tiered Star” Hub USB USB USB USB PC USB USB Device Device Device Device Device
- 24. Host Root Hub Device DeviceDevice Device HUB Device HUB Hot Plug and Play feature Device attachment on Hub port Device is detected Downstream port is enabled Configuration of Device by Host Device USB Configuration Process Enumeration Host Software is responsible for Device configuration Host Root Hub Device DeviceDevice Device Device HUB Device HUB Universal Serial Bus, details Process of Configuration is accomplished via Control Transfers
- 25. USB Transfer Speeds USB 1.1: Low speed is 1.5Mb/s Full speed is 12Mb/s USB 2.0 Low speed is 1.5Mb/s Full speed is 12Mb/s High speed is 480 Mb/s There is a VERY common misconception that say a device is USB 2.0 compliant that it means that it is High Speed device. It does NOT!
- 26. Device Abstractions... - Device Common features and interactions of devices Typically controlled by system software - Function Highest level I/F between device driver and function - End Point Ultimate data source or sink at the device end Each endpoint is unidirectional and has a transfer type associated with it‘s Peripheral
- 27. Endpoints USB Spec: “a source or sink of data” A Control Transfer Type endpoint is bi-directional Others are uni-directional Four address bits plus a direction bit selects between up to 32 buffers (FIFOs) Different USB chips support Various numbers of endpoints Various buffer sizes Each device must have 1 Control Type Endpoint (Commonly referred to as Endpoint 0 or the Default Endpoint)
- 28. Pipes An abstraction used by the USB spec used to indicate that 2 endpoints are joined (one in the PC Host and the other in the device). CONTROL pipe is bi-directional Others are uni-directional
- 29. USB Descriptors Device Descriptors Contains the VID/PID/DID/Serial Number Configuration Descriptors Interface Descriptors Endpoint Descriptors String Descriptors Device Qualifier Descriptors (USB 2.0) Other Speed Configuration Descriptors (USB 2.0) USB “Classes” can add other class specific Descriptors
- 30. OS Interface Requests Transfers The USB Onion Packets Signaling
- 31. Signaling
- 32. USB Signaling USB utilizes differential signaling on the D+ and D- lines. Data is encoded in “non-return to zero with bit stuffing” Bit stuffing is used to ensure enough transitions for the clock recovery circuitry. Most designs use silicon that incorporates an integral Serial Interface Engine (SIE) so you don’t have to worry about the decoding yourself. PCB layout of D= and D- requires care (especially on High Speed devices).
- 33. The SIE (Serial Interface Engine) Serial Interface Engine (SIE) D+ Bytes USB Transceiver D+
- 34. Packets
- 35. USB Packets USB data travels in packets Identified by “Packet ID” (PID) Token packet tells what’s coming Data packets deliver bytes Handshake packets report success or otherwise
- 36. Packet IDs (PIDS) Token Packets IN, OUT, SOF, SETUP Data Packets DATA0, DATA1 (USB LS/FS) DATA2, MDATA (USB HS) Handshake Packets ACK, NAK, STALL (USB LS/FS) NYET (USB HS)
- 37. Handshaking Packets Used to ensure correct data delivery on Control, Bulk and Interrupt Transfers ACK – Received with out Error NAK – Device Busy, has no data Stall – Unsupported Request, Request Failed No Response – Request not received or corrupt, will be retried up to 3 times.
- 38. Packets: Identified by PIDS D A T A 0 D A T A 1 I N O U T A C K N A K S O F S E T U P S T A L L P R E
- 39. Three Packet Types O U T A D D R E N D P C R C 5 Token Packet H D A T A 0 Payload Data C R C 1 6 Data Packet H A C K H/S Pkt D