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SAM7 Controller Area Network

SAM7 Controller Area Network . CAN Agenda. What is CAN ? Why CAN ? CAN Protocol CAN Higher Layer Protocols CAN Applications AT91 CAN Microcontrollers – Roadmap. What is CAN ?. C ontroller A rea N etwork Invented by Robert Bosch GmbH in 1980 for automotive applications

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SAM7 Controller Area Network

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  1. SAM7Controller Area Network

  2. CAN Agenda • What is CAN ? • Why CAN ? • CAN Protocol • CAN Higher Layer Protocols • CAN Applications • AT91 CAN Microcontrollers – Roadmap

  3. What is CAN ? • Controller Area Network • Invented by Robert Bosch GmbH in 1980 for automotive applications • Asynchronous Serial Bus • Simple 2-wire differential bus • Absence of node addressing • Message identifier specifies contents and priority • Lowest message identifier has highest priority • Non-destructive arbitration system by CSMA with collision detection • Multi-master / Broadcasting concept • Sophisticated error detection & handling system

  4. What is CAN ? • The CAN is an ISO standard (ISO 11898) for serial communication • Today CAN has gained widespread use: • Industrial Automation • Automotive, …etc. • The CAN standard includes: • Physical layer • Data-link layer • Some message types • Arbitration rules for bus access • Methods for fault detection and fault confinement

  5. Why CAN ? • Mature Standard • CAN protocol more than 16 years • Numerous CAN products and tools on the market • Hardware implementation of the protocol • Combination of error handling and fault confinement with high transmission speed (up to 1Mb/s) • Simple Transmission Medium • Twisted pair of wires is the standard, but also just one wire will work • Other links works, too: Opto - or radio links • Excellent Error Handling • CRC error detection mechanism • Fault Confinement • Built-in feature to prevent faulty node to block system • Most used protocol in industrial and automotive world

  6. Protocol - CAN Protocol

  7. Protocol - ISO-OSI Reference Model HLPs: CANopen, DeviceNet, OSEK/VDX 7. Application Layer 6. Presentation Layer Partially Implemented by High Layer Protocol (HLP) 5. Session Layer CAN Layers 4. Transport Layer 3. Network Layer 2. Data Link Layer CAN Protocol 1. Physical Layer

  8. Protocol - ISO-OSI Reference Model (2) CAN Controller CAN Transceiver

  9. Protocol - CAN Bus Logic ‘1’ Recessive (r) ‘0’ Dominant (D) Two logic states on the CAN bus Wired-AND Function Bus in dominant state Bus in recessive state or idle

  10. Protocol - Typical CAN Node TXD CAN_H CAN Controller CAN Transceiver CAN Bus µController RXD CAN_L CAN Bus is a simple 2-wire differential serial bus CAN Bus is terminated on each side by a 120 Ohm resistor

  11. Protocol - CAN Bit Coding & Bit Stuffing • Bit Coding : NRZ (Non-Return-To-Zero code) does not ensure enough edges for synchronization • Stuff Bits are inserted after 5 consecutive bits of the same level • Stuff Bits have the inverse level of the previous bit. • No deterministic encoding, frame length depends on transmitted data Number of consecutive bits with the same polarity

  12. Protocol - CAN Bus Access and Arbitration:CSMA/CD and AMP • CSMA/CD: Carrier Sense Multiple Access / Collision Detection • AMP: Arbitration by Message Priority

  13. Protocol - CAN Bus Synchronization • Hard synchronization at Start Of Frame bit • Re-Synchronization on each Recessive to Dominant bit

  14. Protocol - CAN Bit Construction • CAN Bit Period  Four Time Segments • Each Time Segment represents a number of Time Quanta (TQ) • 1 Time Quantum  1 period of CAN Controller Clock • SYNC_SEG: synchronize the different nodes • PROP_SEG: compensate for signal delays across the network • PHASE_SEG1 & 2: compensate for edge phase errors 1 Bit Time  8 to 25 Time Quanta

  15. Protocol - Relation between Baud Rate and Bus Length

  16. Protocol - Frame Formats • SOF: Start Of Frame • CRC: Cyclic Redundancy Code • ACK: Acknowledge • EOF: End of Frame • IFS: Inter Frame Space

  17. Protocol - Frame Formats (2) • CAN V2.0A Standard Frame: Identifier is 11 bits long • CAN V2.0B Extended Frame: Identifier is 29 bits long • ID: Identifier • IDE: Identifier Extension • RTR: Remote Transmission Request • SRR: Substitute Remote Request • RB0/1: Reserved bits • DLC: Data Length Code Our CANs supports CAN V2.0A & CAN V2.0B Specification

  18. Protocol - Frame Formats (3) • Four different frame formats: • Data Frame : RTR Dominant ‘0’ • Remote Frame : RTR Recessive ‘1’ and No Data Field Data Frame has priority on Remote Frame

  19. Protocol - Frame Formats (4) • Error Frame: sent after a violation frame format • Overload Frame: prevents data overflow from a slower CAN Overload Frames are not really used

  20. Protocol - Fault Confinement • CAN Node Error States: • Error Active: Normal state, node can send all frames (error frames included) • Error passive: Node can send all frames excluding error frames • Bus off: Node is isolated from bus • Internal Counters: TEC & REC • TEC: Transmit Error Counter • REC: Receive Error Counter TEC and REC counters allows to prevent from faulty nodes

  21. Protocol - Error Detection Analysis • Error statistics depend on the entire environment • Total number of nodes • Physical layout • EMI disturbance • Automotive example • 2000 hours/year • Baud rate: 500 kbps • 25% bus load One undetected error every 1000 years !!!

  22. HLP - CAN High Layer Protocols

  23. HLP - HLP Definition • CAN protocol defines only the physical and a low data link layer ! • The HLP defines: • Start-up behavior • Definition of message identifiers for the different nodes • Flow control • Transportation of messages > 8bytes • Definition of contents of Data Frames • Status reporting in the system One undetected error every 1000 years !!!

  24. HLP - CANopen • Features • CANopen is a subset from CAL (CAN Application Layer) developed by CiA • Auto configuration the network • Easy access to all device parameters • Device synchronization • Cyclic and event-driven data transfer • Synchronous reading or setting of inputs, outputs or parameters • Applications • Machine Automation • Advantages • Accommodating the integration of very small sensors and actuators • Open and vendor independent • Supports inter-operability of different devices • High speed real-time capability CiA (CAN in Automation)

  25. HLP - DeviceNet • Features • Created by Allen-Bradley (Rockwell Automation nowadays), now presented by the users group ODVA (Open DeviceNet Vendor Association) • Power and signal on the same network cable • Bus addressing by: Peer-to-Peer with multi-cast & Multi-Master & Master-Slave • Supports only standard CAN • Applications • Machine Automation • Advantages • Low cost communication link and vendor independent • Removal and replacement of devices from the network under power CANopen (Europe) – DeviceNet (USA)

  26. HLP - CAN Kingdom • CAN Kingdom is more than a HLP (Meta Protocol): • Introduced by KVASER, Sweden • A ‘King’ (system designer) takes the full responsibility of the system • The King is represented by the Capital (supervising node)s • CAN Kingdom provides simple unique identification of system nodes • Applications • Machine Automation • Advantages • Designed for safety critical applications • Real time performance • Scalability • Integration of DeviceNet modules in CAN Kingdom possible

  27. HLP - SAE J1939 • Features • Developed by Society of Automotive Engineers heavy trucks and bus division (SAE) • Use of the 29 identifiers • Support of real-time close loop control • Applications • Light to heavy trucks • Agriculture equipment e.g. tractors, harvester etc… • Engines for public work

  28. HLP - X-by-wire systems &Time-triggered protocols • Predictable new protocols • Applications • Automotive, aircraft… • TTCAN: Time Triggered CAN: • Robert Bosch GmbH, CiA. • FLexRay: • General Motors, DaimlerChrysler, BMW, Motorola, Philips Semiconductors and Bosch Automotive Group. • TTP: Time Triggered Protocol: • PSA Peugeot Citroen, Audi,Volkswagen, Honeywell and Delphi Automotive Systems. FlexRay is becoming the reference

  29. HLP - OSEK/VDX • Initiative of: • BMW, Bosch, DaimlerChrysler, Opel, Siemens,VW & IIIT of the University of Karlsruhe / PSA and Renault • Goal: Portability and re-usability of the application software • OSEK/VDX includes: • Communication (Data exchange within and between Control Units) • Network Management (Configuration determination and monitoring) • Operating System (Real-time executive for ECU software) • Applications • Automotive • Advantages: Saving in costs and development time Usually called OSEK

  30. Applications - CAN Applications

  31. Applications - CAN: a Large Field of Applications • Building Automation: • Heating control, Air Conditioning, Security, Access & Light Control… • Domestic & Food distribution appliances • Washing machines, dishes cleaner, self-service bottle distributors… • Automotive & Transportation • Dash Board, Power train & Car Body • Train, bus and truck equipment… • Robotic • Production Automation: • Control & link of production machines… • Medical • Agriculture • Harvester, seeding, sowing machines, tractor control...

  32. AT91SAM7 - AT91SAM7 CAN Embedded ControllersA1 - A2 - A3 - X

  33. AT91SAM7 - CAN Controllers Types • 3 types of CAN controllers exist: • CAN Controllers 2.0 Part A: standard frames • CAN Controllers 2.0 Part B Passive or ‘extended frames passive’ • CAN Controllers 2.0 Part B Active or ‘extended frames active’ • CAN Implementations: 2 main implementations strategy • BasicCAN: cheaper CAN Controller • 1 or 2 Rx buffers (FIFO) and 1 Tx buffer • Minimal Filtering • FullCAN: high performance CAN Controllers • Set of buffers called Mailboxes • Dedicated Mailbox Filtering Our CANs: 2.0A/2.0B (Active) & FullCAN

  34. AT91SAM7 - CAN Controllers Features • Two different CAN implementations for the AT91SAM7 family: • CAN embedded in SAM7A1 & SAM7A2 (Europe Technologies CAN) • CAN embedded in SAM7A3 & SAM7X (ATMEL Rousset CAN) • AT91SAM7A1: • 1 CAN Controller 2.0A and 2.0B FullCAN with 16 Mailboxes • AT91SAM7A2: • 4 CAN Controllers 2.0A and 2.0B FullCAN • 1 with 32 Mailboxes, 3 with 16 Mailboxes • AT91SAM7A3: • 2 CAN Controllers 2.0A and 2.0B FullCAN with 16 Mailboxes • AT91SAM7X: • 1 CAN Controller 2.0A and 2.0B FullCAN with 8 Mailboxes SAM7A1-A2 Specific / SAM7A3-X Specific

  35. AT91SAM7 - CAN Controllers Features (2) • Fully Compliant with CAN 2.0 Part A and 2.0 Part B • High Speed CAN: Bit Rates up to 1Mbit/s • Data, Remote, Error and Overload Frame Handling • Mailboxes with the Following Properties: • Standard or Extended ID Programmable for Each Message • Mailbox Configurable in Receive (with Overwrite or Not) or Transmit Modes • Producer & Consumer Mailbox Feature • Independent 29-bit Identifier and Mask Defined for Each Mailbox • Uses a 16-bit / 32-bit Timestamp on Receive and Transmit Messages • Hardware Concatenation of ID Masked Bitfields To Speed Up Family ID Processing • Global 16-bit / 32-bit Internal Timer for Time stamping • Priority Management between Transmission Mailboxes: • Mailbox number prioritization • Message ID prioritization • Autobaud Mode • Automatic retransmission of corrupted messages • Low Power Mode and Programmable Wake-up SAM7A1-A2 Specific / SAM7A3-X Specific

  36. SAM7A3 / SAM7X - AT91SAM7A3 – AT91SAM7XCAN Controller

  37. SAM7A3 / SAM7X - CAN on SAM7X-EK & SAM7A3-EK Boards • PMC has to be programmed 1st for CAN to work: Clock Enabling • Set the PMC_PCER (Peripheral Clock Enable Register). • PIO CAN_TX and CAN_RX have to be configured in peripherals. • CAN Transceiver must be enabled through a PIO configured in Output. • CAN Internal Timer is 16-bit long. • 8 Mailboxes for SAM7X • 16 Mailboxes for SAM7A3

  38. SAM7A3 / SAM7X - CAN Controller Structure

  39. SAM7A3 / SAM7X - CAN Initialization Status Registers Mode Register 0 2 Error Flags CANEN ABM • CANEN = 1: Enable CAN Controller • Wait for bus synchronization (11 consecutive recessive bits are scanned) • WAKEUP flag is set • ABM = 1: Enable Autobaud Mode • Error counters are disabled • Transmission is disabled

  40. SAM7A3 / SAM7X - CAN Bit Timing Configuration Baudrate Register 16 BRP • Sample Point: point in time at which the bus level is read as the value of that respective bit. • 1 Time Quantum  1 period of CAN Controller Clock Time Quantum = (BRP + 1) / MCK TBIT =TSYNC +TPRS +TPHS1 +TPHS2

  41. SAM7A3 / SAM7X - CAN Bit Timing Configuration (2) Baudrate Register 8 0 12 4 PROPAG PHASE2 SJW PHASE1 • Nominal Bit Time: 8 to 25 TQ long. • Information Processing Time (IPT): time required to determine the bit level of a sampled bit. • SYNC_SEG is 1 TQ long. • PROP_SEG: 1 to 8 TQ • PHASE_SEG1: 1 to 8 TQ • PHASE_SEG2 = Max(IPT, PHASE_SEG1) • SJW = Min(PHASE_SEG1, 4TQ) TPRS =TCSC *(PROPAG+1) TPHS1 =TCSC *(PHASE1+1) TPHS2 =TCSC *(PHASE2+1) TSJW =TCSC *(SJW+1) IPT is 2 TQ for ATMEL CANs

  42. SAM7A3 / SAM7X - Low Power Mode Mode Register Status Register 1 20 21 LPM SLEEP WAKEUP • Low Power Mode: Send or receive messages is disabled (Mailboxes inactive) • Enter Low Power Mode: • Set LPM flag • All pending transmit messages are sent before • Wait for SLEEP signal raising • Internal Counter (CAN_TIM) is reset and stuck to 0x0000. • The user can disable CAN Clock (PMC) • Exit Low Power Mode: • Enable CAN Clock (PMC) • Clear LPM flag • Wait for bus synchronization  WAKEUP signal raising • All pending transmit messages are sent before • Internal Counter is reset and stuck to 0

  43. SAM7A3 / SAM7X - Time Management Unit Message Mode Register Mode Register Status Register 0 23 5 4 MTIMEMARK TSTP TTM TEOF • The CAN controller offers optimized features useful to support the Time-Triggered protocols. • Time Management Unit can operate in two modes: • Time Stamping Mode (TTM = 0): the value of the internal timer (CAN_TIM) is captured in the CAN Timestamp register (CAN_TIMESTP) at each: • start of frame (TEOF = 0) • end of frame (TEOF = 1) • Time Triggered Mode (TTM = 1): a mailbox transfer operation is processed when the internal counter reaches the mailbox trigger value (MTIMEMARK field in corresponding mailbox CAN_MMR). • TSTP = 1: A start or an end of frame has been detected

  44. SAM7A3 / SAM7X - Time Management Unit (2) Transfer Cmd Reg Status Register Mode Register 31 22 6 TIMRST TOVF TIMFRZ • CAN_TIM register: Free-running 16-bit timer • TIMRST = 1: Allows to clear the counter • TIMFRZ = 1: Allows to freeze the counter • TOVF = 1: A timer overflow is detected • CAN_TIMESTP register: copy of the CAN_TIM after a successful transfer

  45. SAM7A3 / SAM7X - Data, Remote, Error & Overload Frames Handling Mailbox Status Register Mode Register 23 22 3 7 MRDY MABT OVL DRPT • Data & Remote Frames can be sent/received thanks to the different mailboxes: • A successful transfer raises the Mailbox Ready flag (MRDY) in the mailbox status register. • When a transmit mailbox looses bus arbitration, the transfer request remains pending. • Disable Repeat DRPT = 1: • Transfer request is aborted if the transmit mailbox looses bus arbitration. • Mailbox Abort flag (MABT) in the mailbox status register raises. • Error Frames are automatically handled by the macro. • Overload Frames can be generated by setting OVL flag in the Mode Register: • OVL = 1: an overload is generated after each successful reception.

  46. Mailbox x CAN_MMRx CAN_MAMx CAN_MIDx CAN_MFIDx CAN_MSRx CAN_MDLx CAN_MDHx CAN_MCRx SAM7A3 / SAM7X - Mailbox Organisation • Eight 32-bit registers by mailbox • Mailbox x Mode Register • Mailbox x Acceptance Mask Register • Mailbox x ID Register • Mailbox x Family ID Register • Mailbox x Status Register • Mailbox x Data Low Register • Mailbox x Data High Register • Mailbox x Control Register Mailbox  Channel  Buffer

  47. SAM7A3 / SAM7X - Message Acceptance Procedure Mailbox ID & Acceptance Mask Register 29 MIDE • CAN_MIDx: defines the message ID • MIDE = 0: standard message • MIDE = 1: standard or extended message • CAN_MAMx: defines the mask ID value • Allows a mailbox to receive different messages ID. • CAN_MFIDx: concatenation of ID & mask ID • Speed up message ID decoding

  48. SAM7A3 / SAM7X - Push / Pull Model • Push Model: Classical Tx Rx • Producer  Tx Mailbox • Consumer  Rx Mailbox • Pull Model: • Producer  Producer Mailbox • Consumer  Consumer Mailbox • Consumer transmit a remote frame to the Producer. • Producer transmit the answer to the Consumer. Pull Model: • With Tx Rx mailboxes: 1 Tx+ 1 Rx Mailbox for each node  4 Mailboxes • With Consumer Producer mailboxes: 2 Mailboxes only !

  49. SAM7A3 / SAM7X - Mailbox Object Type Mailbox Mode Register 24 MOT • Five programmable type of mailboxes (MOT field in CAN_MMRx) Reception Mailbox Types: • Receive mailbox: • The first message received is stored in mailbox data registers. • Other messages are ignored by this mailbox. • Receive with Overwrite mailbox: • The first message received is stored in mailbox data registers. • The next message overwrites the previous one. • Consumer mailbox (Enhanced Reception Mailbox): • Sends a remote frame to a producer mailbox. • Waits automatically for a data frame with the same ID from a producer mailbox.

  50. SAM7A3 / SAM7X - Mailbox Object Type (2) Mailbox Mode Register 24 MOT Transmission Mailbox Types: • Transmit mailbox: • Sends either a remote frame or a data frame. • Producer mailbox (Enhanced Transmit Mailbox): • Waits for a remote frame from a consumer mailbox. • Once the remote frame received, sends automatically a data frame with the same ID to the consumer mailbox.

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