© 2000 Morgan Kaufman Overheads for Computers as Components Networking for Embedded Systems zWhy we use networks. zNetwork abstractions. zExample networks.

© 2000 Morgan Kaufman Overheads for Computers as Components Network elements PE network communication link distributed computing platform: PEs may be CPUs or ASICs.

© 2000 Morgan Kaufman Overheads for Computers as Components Networks in embedded systems PE sensor PEactuator initial processing more processing

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components 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

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components Hardware architectures zMany different types of networks: ytopology; yscheduling of communication; yrouting.

© 2000 Morgan Kaufman Overheads for Computers as Components 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

© 2000 Morgan Kaufman Overheads for Computers as Components Bus networks zCommon physical connection: PE 1PE 2PE 3PE 4 headeraddressdataECC packet format

© 2000 Morgan Kaufman Overheads for Computers as Components 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

© 2000 Morgan Kaufman Overheads for Computers as Components Crossbar in1in2 in3 in4 out1 out2 out3 out4

© 2000 Morgan Kaufman Overheads for Computers as Components Crossbar characteristics zNon-blocking. zCan handle arbitrary multi-cast combinations. zSize proportional to n 2.

© 2000 Morgan Kaufman Overheads for Computers as Components Multi-stage networks zUse several stages of switching elements. zOften blocking. zOften smaller than crossbar.

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components I 2 C physical layer master 1master 2 slave 1slave 2 SCL SDL data line clock line

© 2000 Morgan Kaufman Overheads for Computers as Components I 2 C data format SCL SDL... MSBstart... ack...

© 2000 Morgan Kaufman Overheads for Computers as Components I 2 C electrical interface SDL + zOpen collector interface: SCL +

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components I 2 C transmissions multi-byte write read from slave write, then read Sadrs0data P Sadrs1dataP Sadrs0dataSadrs1dataP

© 2000 Morgan Kaufman Overheads for Computers as Components Multiprocessor networks zMultiple DSPs are often connected by high-speed networks for signal processing: DSP

© 2000 Morgan Kaufman Overheads for Computers as Components SHARC link ports zSix per CPU. zFour bits per link port. zPackets have 32- or 48-bit payload. zCan be controlled by DMA. zAre half-duplex---must be turned around by program.

© 2000 Morgan Kaufman Overheads for Computers as Components Ethernet zDominant non-telephone LAN. zVersions: 10 Mb/s, 100 Mb/s, 1 Gb/s 10 Gb/s. zGoal: reliable communication over an unreliable medium.

© 2000 Morgan Kaufman Overheads for Computers as Components Ethernet topology zBus-based system, several possible physical layers: ABC

© 2000 Morgan Kaufman Overheads for Computers as Components CSMA/CD zCarrier sense multiple access with collision detection: ysense collisions; yexponentially back off in time; yretransmit.

© 2000 Morgan Kaufman Overheads for Computers as Components Exponential back-off times time

© 2000 Morgan Kaufman Overheads for Computers as Components Ethernet packet format preamble start frame source adrs dest adrs data payload lengthpaddingCRC

© 2000 Morgan Kaufman Overheads for Computers as Components 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.

© 2000 Morgan Kaufman Overheads for Computers as Components Internet Protocol zInternet Protocol (IP) is basis for Internet. zProvides an internetworking standard: between two Ethernets, Ethernet and token ring, etc. zHigher-level services are built on top of IP.

© 2000 Morgan Kaufman Overheads for Computers as Components IP in communication physical data link network transport presentation application session physical data link network transport presentation application session physical data link network node A router node B IP

© 2000 Morgan Kaufman Overheads for Computers as Components IP packet zIncludes: yversion, service type, length ytime to live, protocol ysource and destination address ydata payload zMaximum data payload is 65,535 bytes.

© 2000 Morgan Kaufman Overheads for Computers as Components IP addresses z32 bits in early IP, 128 bits in IPv6.  Typically written in form xxx.xx.xx.xx. zNames (foo.baz.com) translated to IP address by domain name server (DNS).

© 2000 Morgan Kaufman Overheads for Computers as Components Internet routing zBest effort routing: ydoesn’t guarantee data delivery at IP layer. zRouting can vary: ysession to session; ypacket to packet.

© 2000 Morgan Kaufman Overheads for Computers as Components Higher-level Internet services zTransmission Control Protocol (TCP) provides connection-oriented service. zQuality-of-service (QoS) guaranteed services are under development.

© 2000 Morgan Kaufman Overheads for Computers as Components The Internet service stack IP UDP SNMP TCP User Datagram Protocol FTPHTTPSMTPtelnet