IPZe laboratory Analysis of the communication over USB L Instructor: Straka Martin, Kaštil Jan

Topic of laboratory  The structure of USB Boundary, connectors, topology, speeds  Principles of communication over USB Communication protocol of USB Address, end points, pipes, data, security Type of transaction – control, interrupt, bulk, isochronous Formats of packets Host-device Connected and detection of new device  Application USBtrace properties, analysis, setup IPZ 1/18

Introduction What is USB? Universal Serial Bus (USB) is a serial bus standard to connect devices to a host computer. Hot plug, plug and play. Today, new specification of USB 2.0. Connected and disconnected of device without rebooting the computer or turning off the device USB is intended to replace many varieties of serial and parallel ports. USB can connect computer peripherals such as mice, keyboards, scanners, digital cameras, printers, flash drives, etc... Max 127 devices. IPZ 2/18

Structure of USB IPZ 3/18 Topology – tiered-star topology. Host controller – root of bus (hw/sw – driver). Root Hub – only one, all communications are realized trough root hub. Hubs – one of every level. Device – endpoint device on the different level and speed. Communication between devices not possible! Max 7 levels = max 5 HUBs consecutive. Pipes End points

Structure of USB Connectors – 2 type of connectors. Type A - upstream Type B – downstream Mini-B – downstream Speeds - 3 type of speed. Low Speed – (LS) max. 1.5 Mbit/s - keyboard, mice, track, … Full Speed - (FS) max. 12 Mbit/s – printers, scanner, audio, … High Speed – (HS) max. 480 Mbit/s - flashdisk, HDD drive, video stream, digi-camera … Boundary – 4 wires. 1x power supply, 1x GND Data transfer as different points on 2 wires. HS a FS – shield cabel, max 5 m. LS – not shield, cabel max 3 m. IPZ 4/18

Principle of communication over USB Protocol USB is central-control bus. Every data transfer and control transfer must be initialization by host controller. Communication is defined as transaction – typically 3 packets – polling. –Token packet (Tok) – ID of device, address of end point, pipe, initialized by the host. –Data or „nothing“ – transfer device or host. –Handshake packet (Ack) – receipt of transfer – transfer device or host. IPZ 5/18 Detection of errors – CRC CRC code for control part and data part in every packet. If error –the request for a new packet is generated. –the repair on SW side.

Principle of communication over USB End-point – identification of part of USB device – register for communication. End-point has unique adderss. Max. 15 end-point for every device. End-point „0“ – must have every device, for initialization and configuration of device. IPZ 6/18 PIPEs – virtual path for data transfer between host and end-point of device. stream pipes. message pipes. Default control pipe for initialization and configuration of new device. Half duplex, full duplex. Every pipe has unique address.

Principle of communication over USB Type of data flow – 4 type transfer Control transfers - jsou používány ke konfiguraci zařízení při jeho připojení a mohou být použity k dalším účelům, jako např. k řízení dalších komunikačních rour. Bulk transfers - slouží k přenosům velkého množství dat a jsou na ně kladena nejmenší omezení. Interrupt transfers - k včasnému a spolehlivému doručení dat, nejčastěji pro asynchronní události. Isochronous transfers - zabírají předem smluvené množství přenosového pásma a mají předem dohodnuté zpoždění. Tento druh přenosů je také nazýván proudový přenos v reálném čase. IPZ 7/18

Principle of communication over USB Format of packet – 2 type of packet. Identification of packet (PID) –4 bit PID = 16 type of identification. Control packets – token packets or handshake packets. –PID – identification of packet. –ADDR – address of device. –ENDP – address off end-point. –CRC – security. Data packets –PID – identification of packet. –DATA – data transfer. –CRC – security. IPZ 8/18

Principle of communication over USB Communication layers IPZ 9/18

Application USBtrace Plotny – magnetický povrh pro záznam dat, více ploten nad sebou. IPZ 12/18

Application USBtrace IPZ 13/18 Topology of USB – summary of devices – info of drivers

Application USBtrace IPZ 14/18 Analysis of transactions on USB

Application USBtrace Parameters of communication Type of communication Address of device Address of pipe Address of end-point Length of packet Data etc… IPZ 15/18 transfer data – in bytes

End of presentation Thank you for Your attentions IPZ 18/18