© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Networking for Embedded Systems zWhy we use networks. zNetwork abstractions. zExample networks.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Network elements PE network communication link distributed computing platform: PEs may be CPUs or ASICs.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Networks in embedded systems PE sensor PEactuator initial processing more processing

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Why distributed? zHigher performance at lower cost. zPhysically distributed activities---time constants may not allow transmission to central site. zImproved debugging---use one CPU in network to debug others. zMay buy subsystems that have embedded processors.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Network abstractions zInternational Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model to describe networks: y7-layer model. zProvides a standard way to classify network components and operations.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. OSI model physical mechanical, electrical data link reliable data transport network end-to-end service transport connections presentation data format session application dialog control application end-use interface

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. OSI layers zPhysical: connectors, bit formats, etc. zData link: error detection and control across a single link (single hop). zNetwork: end-to-end multi-hop data communication. zTransport: provides connections; may optimize network resources.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. OSI layers, cont’d. zSession: services for end-user applications: data grouping, checkpointing, etc. zPresentation: data formats, transformation services. zApplication: interface between network and end-user programs.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Hardware architectures zMany different types of networks: ytopology; yscheduling of communication; yrouting.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Point-to-point networks zOne source, one or more destinations, no data switching (serial port): PE 1 PE 2 PE 3 link 1 link 2

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Bus networks zCommon physical connection: PE 1PE 2PE 3PE 4 headeraddressdataECC packet format

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Bus arbitration zFixed: Same order of resolution every time. zFair: every PE has same access over long periods. yround-robin: rotate top priority among Pes. A,B,C fixed round-robin ABCABC ABCABC

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Crossbar in1in2 in3 in4 out1 out2 out3 out4

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Crossbar characteristics zNon-blocking. zCan handle arbitrary multi-cast combinations. zSize proportional to n 2.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Multi-stage networks zUse several stages of switching elements. zOften blocking. zOften smaller than crossbar.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Message-based programming zTransport layer provides message-based programming interface: send_msg(adrs,data1); zData must be broken into packets at source, reassembled at destination. zData-push programming: make things happen in network based on data transfers.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C bus zDesigned for low-cost, medium data rate applications. zCharacteristics: yserial; ymultiple-master; yfixed-priority arbitration. zSeveral microcontrollers come with built- in I 2 C controllers.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C physical layer master 1master 2 slave 1slave 2 SCL SDL data line clock line

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C data format SCL SDL... MSBstart... ack...

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C electrical interface SDL + zOpen collector interface: SCL +

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C signaling zSender pulls down bus for 0. zSender listens to bus---if it tried to send a 1 and heard a 0, someone else is simultaneously transmitting. zTransmissions occur in 8-bit bytes.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C data link layer zEvery device has an address (7 bits in standard, 10 bits in extension). yBit 8 of address signals read or write. zGeneral call address allows broadcast.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C bus arbitration zSender listens while sending address. zWhen sender hears a conflict, if its address is higher, it stops signaling. zLow-priority senders relinquish control early enough in clock cycle to allow bit to be transmitted reliably.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. I 2 C transmissions multi-byte write read from slave write, then read Sadrs0data P Sadrs1dataP Sadrs0dataSadrs1dataP

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Ethernet zDominant non-telephone LAN. zVersions: 10 Mb/s, 100 Mb/s, 1 Gb/s zGoal: reliable communication over an unreliable medium.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Ethernet topology zBus-based system, several possible physical layers: ABC

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. CSMA/CD zCarrier sense multiple access with collision detection: ysense collisions; yexponentially back off in time; yretransmit.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Exponential back-off times time

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Ethernet packet format preamble start frame source adrs dest adrs data payload lengthpaddingCRC

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Ethernet performance zQuality-of-service tends to non-linearly decrease at high load levels. zCan’t guarantee real-time deadlines. However, may provide very good service at proper load levels.

© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Fieldbus zUsed for industrial control and instrumentation---factories, etc. zH1 standard based on MB/s twisted pair medium. zHigh Speed Ethernet (HSE) standard based on 100 Mb/s Ethernet.