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USB

USB. USB RECAP USB COMMUNICATION ELEMENTS USB COMMUNICATION LAYERS PHYISICAL LAYER PROTOCOL ENGINE LAYER APPLICATION LAYER USB PROTOCOL TRANSFER TYPE PACKET FORMAT. RECAP…. USB – automatic attachment, configuration and detachment Speed – low, high and full speed Transfer type

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USB

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  1. USB USB RECAP USB COMMUNICATION ELEMENTS USB COMMUNICATION LAYERS PHYISICAL LAYER PROTOCOL ENGINE LAYER APPLICATION LAYER USB PROTOCOL TRANSFER TYPE PACKET FORMAT

  2. RECAP…. • USB – automatic attachment, configuration and detachment • Speed – low, high and full speed • Transfer type • Isochronous – Bandwidth guaranteed • Asynchronous – Bulk Transfer • USB protocol • Error detection and Recovery mechanism (low BER)

  3. USB communication elements • Host – controls all activities in the bus • HUB – star topology • Attachment.detachment • Power management • Derror detection and correction • Full- low speed device connection • Device - not HOST!

  4. USB communication layers

  5. USB communication layers contd.. • Physical layer • 4 wire cable (+d, -D, +v, GND) • Signalling – Little Endian • RESET • SUSPEND • RESUME • EOP • NRZ I Coding and Bit stuffing

  6. Phsical layer contd. • Serial Interface Engine (SIE) • Part of both Host and device • Encoding (NRZ I), bit stuffing and vice versa • CRC • Detects PID, SOP, EOP, RESET and RESUME

  7. Host Controller • Frame generation • Data Processing (request and response) • Protocol engine (HOST USB protocol interface) • Error handling

  8. 2.The protocol engine layer • Translates data between the application layer and function on device using USB transaction protocol • USB HOST – USB System software • USB device – USB logical device USB system software: • Host software: bandwidth allocation, bus enable, power mangaement

  9. USB software system • Host control driver (HCD) • Interface to the Host controller • USB driver (USBD) • Send the IPRs to the Host software • Send the device description to the client software • Enumeration

  10. USB Logical Device • Collection of End points • Each endpoint have unique address • Each device unique address after enumeration • End point Unidirectional • USB logical device address + End point number + direction IN/OUT = unique Endpoint • Enumeration default pipe + endpoint ‘0’ Control type

  11. 3. Application Layer • Client Software • Transfer data from buffer to endpoint associated with appropriate interface • Function • collection of interfaces

  12. USB Protocol • USB Transaction • Token Phase – future transaction type • Data Phase – data transmission as indicated in the previous token • Handshake Phase – send Handshake packet – success or failure of the transaction • USB - polling Protocol • Handshake Mechanism , timeout rules ,CRC – low BER (10 -10)

  13. Transfer types • Isochronous – Bandwidth gauranteed • Bulk – Bandwidth varies with the system resource • Interrupt – short term – interupts • Control – Enumeration Process

  14. Packet field Formats • SYNC field • Start of each packet • Idle followed “KJKJKJKK” – NRZ I Encoding • K - ‘0’ / ‘1’ > 20 ms (Full speed/ High speed) • J – ‘1’ – one bit time • Synchronize the internal clock in the Device

  15. PID (Packet Identifier) • Actual PID – 4 bits • I’s complement - 4 bits – error detection • PID groups • Token – IN, OUT, SOF SETUP • Data - data0 or data1 • Handshake – ACK, NAK, STALL

  16. Address field • 7 bits • 127 device address • 0 reserved address

  17. Frame, Data fields • Frame field • 11 bits only in SOF token • Indicates the number of the current frame • Data field • up to 1024 bytes

  18. CRC field • Protect all fields • Absent in the PID • Token – 5 bits • Data – 16 bits

  19. Packet formats • Token Packet  • Start Of Frame Packet

  20. Packet Formats Contd.. • Data Packets • Handshake Packets

  21. Transaction Format • Control Transfer • SET_ADDRESS : setting a permanent address to a function.   • GET_DEVICE_DESCRIPTOR: the host wishes to get the device descriptor, which contains details concerning the device - how many configurations, interfaces it has, is the device is self/ bus powered etc. • GET_CONFIGURATION_DESCRIPTOR: the host wishes to learn about a specific configuration of a device. • GET_CONFIGURATION: the host detects which configuration is active at the moment in the device. • SET_CONFIGURATION: the host sets a specific configuration on the device.

  22. Control Transfer

  23. Bulk Transfer • IN transfer - in which the host asks for data from the device - data flow direction is from the device into   the host. • OUT transfer - in which the host whishes to send data to the device - data flows from the host out to the device.

  24. Bulk Transfer - OUT

  25. Bulk IN transfer

  26. Interrupt Transfer

  27. Isochronous Transfer

  28. Reference • USB Explained by Steven McDowell & Martin D.Seyer 1999. • Universal Serial Bus Specification Revision 1.1 Sep 1998 (Compac, Intel,  Microsoft, NEC)

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