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Advanced Embedded Systems Design

Advanced Embedded Systems Design. Lecture 10 Controller Area Networks BAE 5030 - 003 Fall 2004 Instructor: Marvin Stone Biosystems and Agricultural Engineering Oklahoma State University. Goals for Class Today. Questions over reading / homework ( Chapters 23, 24 )

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Advanced Embedded Systems Design

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  1. Advanced Embedded Systems Design Lecture 10 Controller Area Networks BAE 5030 - 003 Fall 2004 Instructor: Marvin Stone Biosystems and Agricultural Engineering Oklahoma State University

  2. Goals for Class Today • Questions over reading / homework (Chapters 23, 24) • USB from a developers prospective – (Patrick) • SPI and I2C – (Brody) • Controller Area Networks introduction – (Stone) • Set assignment

  3. Automotive SAE J1850 SAE J1708 / 1587 CAN based SAE J1939 / ISO 11783 Fault tolerant busses ByteFlight FlexRay TTP / TTCAN MOST Avionics MIL-STD-1553 ARINC 429 Marine NMEA 0183 NMEA 2000 (IEC 61162-3 ) Ethernet Ethernet IEEE 803.2 – Further defined ethernet 803.11 – wireless LAN 802.15.4 – Zigbee LIN On-board busses (inter-IC busses) SPI I2C Microwire 1-Wire Industrial MODBUS RS485 Ethernet Fieldbus Bitbus CAN DeviceNet SDS CiA Proprietary RS 485 CAN Communications busses for embedded systems(A very abridged list!)

  4. CAN – Controller Area Network - Introduction • History • Developed by Bosch in mid 1980’s to meet a need for networking ECUs (electronic control units in automobiles) • Initially introduced with an 11-bit message identifier (CAN 1.0 – 1.2), later a 29 bit identifier introduced (CAN 2.0) • Now: • 11 bit only parts: CAN 1.2 (Also CAN2.0A) • 2048 different CAN messages • 11 bit compatible with 29 bit messages: CAN 2.0B 29 bit passive • xmit and receive 11 and 29 bit ID: CAN 2.0B • 536 million CAN messages • CAN has since been heavily adopted • ~350 million protocol controllers sold in 2003 (Bosch / CiA) • Broad industrial support • Automotive • J2284 / IDB-C 500 - kBaud automotive physical and data link • J1939 – Heavy duty vehicle physical/data link/network/app layer • Proprietary • Industrial • DeviceNet – Industrial physical/data link/network layers • SDS - Industrial physical/data link/network layers • Proprietary • See: http://www.can-cia.de/can/protocol/history/history.html

  5. CAN Overview • CAN = Controller Area Network • Serial data communications protocol for real-time application using a multiple access bus • Messages have assignable priority • most critical can dominate during heavy load • Messages are short (controlled length) • opportunities to insert a new message come often • Asynchronous serial communications • Serial bus vs. point-to-point • Reduction in wiring complexity • Better information sharing • Low probability of an undetected error • 4.7 x 10-11 x message error rate • For a message error rate of 25/sec: 1 undetected error per 10,000 hours operation

  6. Capacity Comparison

  7. Capacity and Performance • Use of bus bandwidth @250 kBaud by messages • 100 messages per second (10 ms repetition) =5% • Torque/Speed control on engine • Hitch control • 10 messages per second (100 ms repetition) =0.5% • Throttle position • GPS Lat/Lon data • Implement application rate control (process data) • 1 message per second (1s repetition) =0.05% • Display updates • System status

  8. Message latency • 134 bit message @250 kBaud (bit stuffing ignored) • @ 4 ms per bit = 536 ms = 0.5 ms per message max • Highest priority message • must wait no more than ~0.5 ms • Low priority messages • must wait till higher priority messages clear • latency may be long at high bus loads

  9. Conventional Wiring (No Bus) Serial Communication Links

  10. A Simple CAN Application (Serial Bus)

  11. CAN - Introduction • Network structure • Intended as a bus, but other physical implementations are possible • Limitations – No “Tee’s”

  12. An overview of CAN based networking • CAN - Elements • CSMA/CA • Bitwize priority access strategy • Uses distributed synchronization of bit timing • Non-destructive collisions • Message components • Identifier / Data • Bus Access - Arbitration / Prioritization • Error Detection / Error Confinement • Filtering • Other features • In Frame Acknowledgement • RTR

  13. Message structure • Message frame contains: • 11/29 bit Identifier • Data length • 0-8 bytes data • CRC • In-frame acknowledgement

  14. CAN Frame Format - CAN 2.0B

  15. Typical ECU Components

  16. ECU Connection to the bus ECU 1 ECU 2 CAN_H CAN_L TBC_PWR Terminator Terminator CAN_H CAN_L TBC_RTN

  17. Message Message Physical network structure Message Message

  18. Message Components 11 bits or 29 bits Message (up to 150 bits) 0 to 8 bytes (0 to 64 bits) Identifier Data Start Serial bit stream

  19. CAN Arbitration ISO 11878 Lower numbered identifiers assume higher priority

  20. Bit time control – Length of a single bit • Bit must arrive a destination before phase_seg1 begins. Sampling at receiver will occur within the phase segment. • Prop_seg. should accommodate total out and back propagation time plus delay in tranceivers

  21. CAN synchronization / bit timing • Definitions: • Synchronization segment (Sync_Seg) - that part of the bit time where bit edges are expected to occur • Propagation segment (Prop_Seg) - intended to compensate for the physical delay times • Phase segment (Phase_seg1, Phase_seg2) – Provide control of the sample point position • Synchronization Jump Width (SJW) defines how far a resynchronization may move the Sample Point inside the limits defined by the Phase Buffer Segments to compensate for edge phase errors. • Synchronization • Hard synchronization will be done to align bits at the beginning of a message. • Phase_seg1 is lengthened or phase_seg2 is shortened to minimize phase error by up to the synchronization jump width (SJW). Larger phase errors cannot be compensated for. • See:http://www.can.bosch.com/docu/CiA99Paper.pdf

  22. Physical Layer • Many physical layer definitions • Most ISO 11898 based • Maximum number of ECU's • Typical 30 (per segment) • Typical Media • Twisted shielded pair • 120 W nominal impedance • Two data lines (CAN_H, CAN_L) • One shield • Twisted Quad un-shielded • 75 W nominal impedance • Two data lines (CAN_H, CAN_L) • Two termination supply lines • Signal • Compatable with ISO 11898 drivers (eg. Phillips 80C250)

  23. ISO 11898 Bus levels – Microchip AN 228

  24. Mapping of CAN to the OSI – Microchip AN 228 • Characteristics of CAN - CAN provides Data Link functions

  25. To form a complete communications system ISO 7498

  26. Message Filtering - Example Accept if: (ID AND MASK) XOR MATCH = 0 10111100100 IDENTIFIER 1 = Care, 0= Don’t Care 11100000000 MASK 10100000000 = ID AND MASK Pattern must match 10100000000 MATCH 00000000000 = (ID AND MASK) XOR MATCH

  27. Error Detection • 5 Error Types Detected • Bit Error (Sent bit doesn’t match monitored bit) • Stuff Error (more than 6 successive in one state) • CRC error • Form Error • Acknowledge Error • Probability of an undetected error • 4.7 x 10-11 x message error rate • for a message error rate of 25/sec, 1 undetected error per 10,000 hours operation

  28. Assignment • Install the Pont time triggered scheduler in hardware and toggle the RED/GREEN LED at 1 per sec. • Read Pont, Chapter 25, 28 • Tutorial – 30 min • Review SAE J1708, SAE J1850, SAE J1939 • or • Review DeviceNET and SDS

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