USB: UNIVERSAL SERIAL BUS Joe Kaewbaidhoon Alex Motalleb Vishal Joshi Prepared for EECS 373 University of Michigan, Ann Arbor 1

2  What do we use to connect a device to a computer? dellcomputer.jpg drives.ecoustics.com/d/f/USB-3.0

USB  The most widely used hardware interface for connecting peripheral devices to a computer.

History  Developed in the mid 1990’s by Compaq, DEC, IBM, Intel, Microsoft, NEC, Nortel  Purpose:  Reduce cabling  Reduce type of ports  Simplifying software configuration  More efficient transfers, higher data rates  Versions: 1.0, 2.0, and 3.0 4

5  How do we physically connect a device?

Connectors  Single master, up to 127 slaves  Type A (faces upstream)  The connector found on host and hubs  Type B (faces downstream)  The connector found on slave devices  miniA, miniB, and several other types used for smaller devices 6

Pins/wires  4 pins  Ground  V cc : power the devices (5V output from master), note that some devices can draw power from 2 USB ports  2 data lines (D + and D - ) Twisted Pair Differential Transmission: If D + - D - > 200 mV, send ‘1’. If D - - D + > 200 mV, send ‘0’. Polarity switches with speed 7

J-K state 8  Polarity switches with speed  J and K are logical states Hi-speed differential signal Low-speed differential signal J state10 K state01

9  Once connected, how does the hardware communicate?

Protocol Terms  Hub:  Connects slaves to host (master)  Endpoint: a logical entity, found on a device. A USB connection may have up to 32 endpoints (16 for master and 16 for slave) in one connections  Pipes: connection from one endpoint to another 10 vd-rom/cd-rw_slim_external_combo_drive

Endpoint Example 11

Hardware Initialization 12  Hub port has status bits  plugged in, status bit = 1  Idle = 0  Hub automatically updates when something plugs in  Host polls the status bits  If 1, initializes the hardware and software protocol

Powering a Device with V cc  Devices can be powered using the V bus (V cc ) line  Functions divided into three types  Low-power bus powered function May use up to one unit load (100 mA)  High-power bus powered function May use up to 5 unit loads (500 mA) after configuration  Self-powered function May use up to one unit load Rest of the power supplied by external source 13

Transfer Speeds on D + and D -  Low speed = KB/s  Used for Human Interactive devices (ex. keyboard, mouse, etc)  Full speed = 500 KB/s – 10 MB/s  Used for audio and compressed video (ex. Microphone)  High speed = MB/s  Used for video and storage (ex. Digital camera) USB 1.0 USB

Drivers  Once the connector is plugged in, the host detects and interrogates it  Loads appropriate driver based on PID/VID (Product ID/Vendor ID) combination  VID provided by USB Implementer's forum for a fee 15

16  Once connected and synchronized, how is the software going to facilitate communication?

Hierarchy of Data Transfers 17

Hierarchy of Data Transfers 18

Transfers  Control: used for command and status operations  Most common type of transfer  Interrupt: a polling transfer which checks devices for interrupts  Isochronous: continuous, periodic transfers  Generally used for audio or video streaming  Bulk: used for large bursts of data  Example: print-job, scanner image 19

Hierarchy of Data Transfers 20

Stages  Typical stage involves three types of packets  Token: Describes what follows, read/write, address of device, designated endpoint  Data (optional): Carries the payload Low speed – 8 bytes Full speed – 1023 bytes High speed – 1024 bytes  Status: reports whether data/token was received, if endpoint stalled 21

Control Transfer: Setup Stage  Setup Stage: 3 packets – Token, Data0, Ack 22

Control Transfer: Data Stage  Data Stage: IN or OUT depending on direction of transfer 23

Control Transfer: Status Stage  Status Stage: IN or OUT depending on direction of transfer 24

Hierarchy of Data Transfers 25

Packet Types  Token Packets  In: Host requests read  Out: Host requests write  Setup: Used to begin control transfers  Data Packets  Data0  Data1  Handshake Packets  ACK: Successfully received  NAK: Failed to receive (also used during interrupts)  STALL: Host must intervene 26

Hierarchy of Data Transfers 27

Packet Fields  Sync: 8-32 bits used to synchronize host clock with device clock  Packet ID (PID): defines the type of packet being sent  Sent as 8 bits ->  ADDR: specifies which device the packet is being sent to  7 bits for addressing to 127 slaves  Address 0 is invalid 28 shell/usb3.shtml

More Packet Fields  ENDP: defines the target endpoint  4 bits for 16 possible endpoints  Endpoint 0 must exist  CRC: Cyclic Redundancy Checks  5 bits within token  16 bits within data  EOP: End of packet 29

Data Encoding  Uses NRZI (Non Return to Zero Inverted)  Transition -> 0  No transition -> 1 30 Adapted from

Bit Stuffing 31  Bit stuffing after 6 th consecutive ‘1’

Questions? 32

References   