Protocole CAN et Multiplexage Automobile

Transcription

1 Protocole CAN et Multiplexage Automobile Nov Dec 2010

2 1) Introduction Electronique automobile Véhicule multiplexé. 2) Le protocole CAN Introduction Trame CAN L arbitrage, gestion de collisions, acquittement Différents types de trames et implémentation Bit timing et synchronisation Détection et gestion des erreurs Les normes ISO and SAE La couche physique, codage du bit 3) Mise en œuvre Registres de contrôle dans le Microcontrôleur Développement d une application CAN Messagerie 4) Conclusion Autres Bus de communication Bibliographie Contenu 1

3 Vehicle equipment trends 2

4 1: Power train Ignition, Injection Direct Injection Gear box/clutch Automatic transmission Stop and Go Regenerative braking Hybrid Fuel economy & pollution control 3: Infotainment Navigation Display Video Vehicle equipment trends 2: Body and comfort Central locking, remote access Anti thefts (coded key) Power window Interior lighting (dimming etc) Wiper (intermittent/rain sensor) Electric mirror Seat: electric control and heat Radio Air conditioning Trip computer/dashboard Park assistance 3

5 Vehicle equipment trends - safety 4: Safety Air bag ABS, ESP & Traction control Tire pressure monitor Radar Night vision Head up display Line departure Increase safety, active and passive 4

6 Vehicle electronic architecture Trip computer Dashboard Radio Engine management AirBag ABS/ESP Air Cond. Communication bus Top column switches Light, wipers, radio, horn, cruise control Front Light control Turn signal, head lamp, fog Rear module Light, turn signal, brake, rear wiper Driver Door Lock, window, mirror, switch panel Passenger Door Body Controller Interior light, Front wiper, RF, Alarm 5

7 illustration of multiplexing Switch status Vehicle speed Speed acquisition AC ON Trip computer Dashboard Radio Engine management AirBag ABS/ESP Air Cond. Top column switches Light, wipers, radio, horn, cruise control Front Light control Turn signal, head lamp, fog Rear module Light, turn signal, brake, rear wiper Driver Door Lock, window, mirror, switch panel Passenger Door Body Controller Interior light, Front wiper, RF, Alarm Direct Load and actuator control: Top column switch: Lights, front and rear wiper, cruise control, radio etc Indirect and advance actuator control: Air conditioning ON/OFF: engine management. Dashboard: Engine temperature and speed: Rear gear ON & front wiper ON: automatic turn ON of rear wiper Door open/close: turn ON/OFF interior light, displayed on the dashboard for safety Child safety: lock rear doors, lock rear power window Key identification for door open/close & engine start (anti theft) Vehicle speed used by: Engine control: for engine parameter Dashboard: display vehicle speed Trip computer: for calculations. Radio system: adjust level versus speed Locking system: automatic lock when speed >7km/h Front wiper: use this data to adapt intermittent period & select lower speed when vehicle is stopped (ex: speed 1,stop at traffic light=>intermittent active) 6

8 Network architectures Flat Network CAN Multiple Flat Networks Low speed High speed CAN Multiple and Hierarchical Networks Gateway node CAN (VAN) LIN sub buses Multiple CAN networks to optimize data transfer and bus speed Subnets are necessary to reduce bus load on main CAN Bus Increase robustness Gateway nodes between CAN buses and CAN & LIN buses 7

9 Automotive CAN and LIN networks CAN LIN Mirror LIN WL Lock Lock Gateway WL Leveling Lights Flaps 1-10 CAN LIN Heater LIN CAN Lights Power Train Control Fan CAN Climate Control Central Body Controller Dashboard Wiper Power Seat Power Seat LIN Heater ROOF CAN Rear Power Seat LIN Heater Heater Wiper Lock Lights CAN Lights Leveling LIN Gateway LIN Lock WL Mirror WL Lock 8

10 Body (Comfort, Safety, Lighting, Instrumentation) Example: car network architecture Intell. Transportation & Communication Power Train Chassis CAN-B Instrument. CAN-C Climate Ctrl Left Door Module Ctrl Panel Lighting Ctrl Central ECU & Gateway CAN (diagnostics) Stepper Motor LIN Climate Panel Stand-By Heating Right Door Module Sun-Roof Wiper Wish-Wash Remote Keyl.Entry Air Bag Sensor Squib Seat Control LIN DC Motor Light Level Regulation Park-Dist Ctrl CD TV-Tuner Video Mod Multi Funct Steering Wh Multi Funct Display Mobile Ph Navigation Radio HiFi DSP Video Monitor ITS-Bus D2B, MOST Engine Ctrl Gear Box Ctrl Vehicle Dynamics FlexRay Solenoid Electric Brake E-Power Steering 9

11 High-End Network Architecture Examples BMW, Mercedes-Benz 10

12 Power management, MCU power supply System low power and wake up management Include physical layer Supply Typical View of an Automotive ECU Typical Electronic Control Unit Power Supply Watchdog, Interrupt SPI interface Micro Controller Power Drivers Loads Interface to high speed CAN bus CAN bus CAN bus Low power mode Wake up High Speed CAN SBC Low speed CAN Transceiver Switch Detection Interface RF Transceiver LIN Transceiver LIN sub-bus Switches Switch detection interface Interface to low speed CAN bus Interface to local sub bus 11

13 CAN protocol: Controller Area Network

14 CAN: Controller Area Network ISO standard, developed by Bosch in the 80 s. Automotive and Industrial applications (Airplane industry) Robust, handle well extreme condition, error detection and recovery, fault confinement Event trigger protocol Priority and arbitration mechanism Multi master Open architecture 3 bus speed ranges with specific Physical layer implementation Single wire, low speed (<125kb/s), high speed (< 1Mb/s) 13

15 ISO / OSI Structure of a CAN Node OSEK COM/NM, Vector Driver S/W mscan,toucan CAN-B, CAN-C Transceivers OSI Layers APPLICATION PRESENTATION SESSION TRANSPORT NETWORK DATA LINK PHYSICAL CAN Protocol DATA LINK LAYER LOGICAL LINK CONTROL (LLC) SUB-LAYER - Acceptance Filtering - Overload Notification - Recovery Management MEDIUM ACCESS CONTROL (MAC) SUB-LAYER - Data Encapsulation/Decomposition - Frame Coding (Bit Stuffing/Unstuffing) - Medium Access Management - Error Detection/Signaling - Acknowledgement - Serialization/Deserialization PHYSICAL LAYER - Bit Encoding/Decoding - Bit Timing - Synchronization 14

16 Simplified Electronic Control Unit system partitioning Power supply Micro-controller Sensor and Load Driver Protocol Handler Data Physical interface ECU Physical bus ECU: Electronic Control Unit 15

17 CAN: Controller Area Network CAN Frame segmentation Identification & Arbitration Data Integrity Check Acknowledge Data: ex vehicle speed, engine temperature, door open-close Encapsultated in the CAN frame with identification and integrity check 16

18 CAN: Controller Area Network CAN Frame segmentation Acknowledge Identification & Arbitration Data Integrity Check Data: ex vehicle speed, engine temperature, door open-close Encapsultated in the CAN frame with identification and integrity check 17

19 CAN 2A and 2B 18

20 Arbitration principle bus SOF ARBITRATION FIELD: IDENTIFIER Node 1 Node 2 Node 3 node 1 node 2 Two states for the bus: Recessive (weak, transistor(s) OFF) Dominant (strong, transistor(s) ON) Wired OR function: dominant level overwrite recessive level. Bus state is monitored: => Sending a recessive bit and reading a dominant bit means loss of arbitration Identifier is unique to a Node node 3 Node 2 arbitration loss Node 1 arbitration loss bus dominant state recessive state - Several nodes starts to send message at the same time. - Only one will win arbitration, and will send its message. - The other(s) will retry after message completion. - No time and no information is lost. 19

21 Inter frame, Acknowledge bits, Arbitration Arbitration phase Inter frame delay Acknowledge bit Tx1 and Tx3 send a recessive bit Bus Bus Tx1 Tx1 Tx2 Rx1 Tx2 Tx3 Tx3 send Rx1 Rx2 Rx3 Tx3 Tx1 and Tx3 send dominant Rx2 Rx3 - Tx3 send dominant - Tx1 send recessive Rx1 = recessive => node 1 losses arbitration and stop transmission 20

22 Tx1 Tx2 Acknowledge bit illustration Stronger drive for acknowledge bit Tx1 send dominant Bus Bus Tx1 Tx2 Rx1 Rx2 Tx1 Tx2 Rx1 Rx2 Tx2 transmit. Tx2 recessive for ACK bit Zoom on acknowledge bit: 21

23 Example: 3 nodes monitored Bus Tx1 Tx2 Tx3 Rx1 Rx2 Rx3 3 Tx/Rx, Inter frame, Acknowledge bits, Arbitration 22

24 CAN Data Frame recessive dominant IFS or Bus Idle SOF 1 bit Arbitration Field 12 bits (Std ID) 32 bits (Ext ID) Control Field 6 bits Data Field 0-8 bytes CRC Field 16 bits ACK 2 bits EOF 7 bits IFS Bit Stuffing A node is allowed to start transmitting a Data Frame after Inter-Frame Space (IFS). The two complementary bus values are called dominant and recessive. All receivers synchronize to leading edge of Start Of Frame (SOF). Arbitration Field is 12 bits for a Standard Format Data Frame (CAN2.0A/B). Arbitration Field is 32 bits for a Extended Format Data Frame (CAN2.0B only). Bit Stuffing - whenever 5 consecutive bits of equal value are transmitted, 1 extra bit of complementary value is automatically inserted into the bit stream: provides edges for clock resynchronization. Receivers automatically de-stuff. 23

25 Messages are one of four different types, called frames : CAN : Message Types Data Frame: transmits up to 8 bytes of data Remote Transmission Request (RTR) Frame: requests a Data Frame Error Frame: indicates a bus error (independent of CPU) Overload Frame : creates an extra delay between Data Frames or Remote Frames An Inter-frame space is also defined. Only Data and RTR Frames can be transmitted under host control. 24

26 Requirements of a CAN Controller Simple user interface to CPU Access control & status registers Access to buffers Interrupt and error types Message filtering & buffering Store incoming & outgoing messages Only interrupt CPU w/ relevant messages Predictable Message Transmission Protocol handling Error Detection Arbitration detection Bit monitoring/stuffing Physical layer interface Current & voltage control for bus Absorb transients Signal bus (line) faults & correction CAN bus CANH CANL Physical interface CAN Transmit Receive Engine TX RX H/W Errors Microcontroller Message filtering + buffering Control + status CPU Interface 25

27 mscan12 - Rev 2.0 (for HCS12 MCUs) mscan Receive / Transmit Engine Global Identifier Filtering: Internal Priority Scheduling 2 x 32-bit CPU Interface (Memory Mapped I/O) TX Buffer TX Buffer TX Buffer Priority Register or 4 x 16-bit or 8 x 8-bit RX Buffer RX Buffer RX Buffer RX Buffer RX Buffer 26

28 Bus Tx1 Tx2 Rx1 Rx2 CAN Bit Timing SYNC_SEG: The bit edge is expected to lie within this segment. PROP_SEG: Allowance for physical delays. PHASE_SEG1 & PHASE_SEG2: Define the position of the Sample Point. May be adjusted to compensate for edge phase errors. SAMPLE POINT: The bus value at this point is taken as the value of the bit (if 3 samples per bit taken, this is position of 3rd sample). BIT TIME SYNC_SEG PROP_SEG PHASE_SEG1 PHASE_SEG2 Transmit Point Sample Point - Each segment is composed by one or more Tq (time Quanta). - Each Tq have same value, derivate from the main MCU clock. 27

29 Extract from CAN config file: // fnbt = bit/s // CANCLK = Hz // tbus = 25 ns (0.5 m * 5*10^-9 sm^-1) // ttx = 500 ns // trx = 500 ns // // NBT = 10 // Tq = 0.75ns // P = 3 // SYNC_SEG = 1Tq // PROP_SEG = 3Tq // PHASE_SEG1 = 3Tq // PHASE_SEG2 = 3Tq // RJW = 3 // OscToll = % // 28

30 Tx1 Tx2 CAN Clock Resynchronization Edge appears here... Edge should be here... Edge appears here... CAN bus r d Edge should be here... Receiver bit timing Sample points S PS P1 P2 S PS P1 P2 S PS P1 P2 S PS P1 P2 S PS P1 P2 BIT 1 BIT 2 BIT 3 BIT 4 BIT 5 S = SYNC_SEG PS = PROP_SEG P1 = PHASE_SEG1 P2 = PHASE_SEG2 Bit 3 Negative Phase Error PHASE_SEG2 shortened Bit 5 Positive Phase Error PHASE_SEG1 lengthened 29

31 Bit Error - Stuff Error - CRC Error - Form Error - CAN Error Detection Detected by a transmitter if the bit value received is different from the bit value transmitted. Exceptions:- sending a recessive bit and receiving a dominant bit during the Arbitration Field or the Ack Slot, or during a Passive Error flag. Detected by a receiver if 6 consecutive bit values are received during a message field that should be encoded by bit stuffing. Detected by a receiver if the CRC calculated by the receiver is different from the CRC received in the CRC Sequence field. Detected by a receiver if a fixed form bit field contains one or more illegal bits. Acknowledge Error - Detected by a transmitter if it does not receive a dominant bit during the ACK Slot. 30

32 CAN Terminology Revealed CAN Robert Bosch CAN Specification, Revision 2.0 CAN 2.0 A CAN 2.0 B Full-CAN MSCANxx TouCAN FlexCAN - Formerly CAN 1.2, limited to 11-bit identifiers - Usually means complete protocol standard - Includes 11-bit and 29-bit identifiers - Should read CAN 2.0 A/B - Hardware implementation with at least 15 message buffers - Nothing to do with compliance to CAN 2.0 A/B standard - Freescale Scalable CAN hardware implementation (HC08, HC12, HCS12, DSP families) - Full-CAN Freescale CAN hardware implementation (DSP, PowerPC families) - Similar to, but larger version of TouCAN 31

33 ISO and SAE Standards for CAN ISO : Protocol ISO : Time trigger CAN Physical layer: Dual wire ISO : high speed CAN (up to 1Mb/s) ISO : low speed fault tolerant CAN (10-125kb/s) ISO : high speed CAN with low power mode Upgrade of Physical layer: Single wire Single wire CAN: GM3089 (SAE). 32

34 High speed CAN physical layer implementation

35 High speed CAN full view +5V 2.5V 25k Rxd sleep hz 25k Differential receiver driver CAN H Bus termination 120 Txd BUS Dominant state VcanH 0 1 4V Txd CAN L 2.5V Vdiff Vbat wu Wake up receiver driver +5V Rxd Recessive state VcanL 1V gnd Sleep state on/off SPLIT Splitted termination 34

36 High speed CAN transmit and receive mode (1) 2.5V 25k +5V Txd Dominant state 0 1 Rxd Txd 25k Differential receiver driver CAN H 120 CAN L 120 BUS 2.5V Recessive state VcanH Vdiff VcanL 4V 1V driver High side switch to Vdd (5V) Low side switch to gnd Diode function Bus termination Rxd 2 bus levels: recessive & dominant Signal symmetry in DC and during transition Power dissipation, current in bus load and bus driver 35

37 High speed CAN transmit and receive mode (2) 2.5V 25k +5V Txd Dominant state 0 1 Rxd Txd 25k Differential receiver driver CAN H 120 CAN L I-canH I-canL 120 BUS 2.5V Recessive state VcanH Vdiff VcanL 4V 1V driver Bus termination Rxd High side switch to Vdd (5V) Low side switch to gnd Diode function 2 bus levels: recessive & dominant Signal symmetry in DC and during transition Power dissipation, current in bus load and bus driver I-canH 0 0 I-canL I-canH+I-canL 0 36

38 Physical Interface - High Speed CAN ISO or -5 Linear bus topology 500 Kb/s bit rate 40m max bus length 3.5V 2.5V 1.5V CANH CANL recessive dominant recessive ECU 1 ECU 2 ECU n... Stubs 1m RT 120Ω CANH CANL Twisted-pair, or parallel, non shielded media RT 120Ω Terminators can be inside end ECUs 37

39 Physical interface on MCU board 38

40 CAN network and signals 3 Tx/Rx, Inter frame, Acknowledge bits, Arbitration Tx5 Tx1 Tx2 Tx3 Tx4 5 nodes lab network Bus Tx1 Tx2 Tx3 Rx1 Rx2 Rx3 39

41 Inter frame, Acknowledge bits, Arbitration Arbitration phase Inter frame delay Acknowledge bit Tx1 and Tx3 send a recessive bit Bus Bus Tx1 Tx1 Tx2 Rx1 Tx2 Tx3 Tx3 send Rx1 Rx2 Rx3 Tx3 Tx1 and Tx3 send dominant Rx2 Rx3 - Tx3 send dominant - Tx1 send recessive Rx1 = recessive => node 1 losses arbitration and stop transmission 40

42 CAN register control and CAN development Tools

43 MSCAN What must be common to each node on the same network? - Baud rate - CAN2A or 2B (standard or extended identifier) - Bit partitioning, but timing, but sampling point - Messaging structure (ID and data) In addition, each application must manage and define: - Filtering mechanism - INT handling etc 42

44 CAN module registers Configuration Transmission and reception management Acceptance / Mask ID Transmit / reiceive buffers 43

45 CAN register control 44

46 Each module is developed by a different system supplier: Development phase of the vehicle Trip computer Dashboard Radio Engine management AirBag ABS/ESP Air Cond. Top column switches Light, wipers, radio, horn, cruise control Supplier A Front Light control Turn signal, head lamp, fog Supplier B Read module Light, turn signal, brake, rear wiper Supplier C Driver Door Lock, window, mirror, switch panel Supplier D Passenger Door Body Controller Interior light, Front wiper, RF, Alarm CANalyser tool Front Light control Turn signal, head lamp, fog CAN tool Emulate other nodes messaging. Test, debug and validation Supplier B 45

47 CANalyser tool 46

48 ID data Messaging definition: example Trip computer Dashboard Radio Engine management AirBag ABS/ESP Air Cond. Top column switches Light, wipers, radio, horn, cruise control Front Light control Turn signal, head lamp, fog Rear module Light, turn signal, brake, rear wiper Driver Door Lock, window, mirror, switch panel Passenger Door Body Controller Interior light, Front wiper, RF, Alarm 15 Front light 20 Door 10 switches Warning Turn signal left Turn signal right wiper Front light Message periodicity: -Every x ms -Upon switch state change signals 47

49 Signals: Driver door: close/open, window up/down, passenger window up/down Passenger door: close/open Commodo status: wiper on/off, head lamp, turn signal Vehicle speed: CAN frame construction For each ECU, consolidate signals into one or more frame Example of CAN data frame Network management messages Node identification. Network phase life (phases de vie) 1 ECU of the vehicle managed the network (OSEK VDE) 48

50 speed [ bit/s ] Multiplexing protocols embedded control multi media 25M 10M 1M CAN-C dual wire Flexray, TTP time triggered, fault tolerant 2x2 wire / optical TT CAN D2B, MOST optical ring Bluetooth 125K 20K 10K LIN master-slave single wire J1850 (US market) ISO 9141 diagnostic CAN-B fault tolerant dual/single wire wireless medium Complexity and Relative cost per node Not shown: dedicated air bag protocols and proprietary buses (i.e DSI, BMW K-bus) 49

51 protocol overview Protocol engine UART SCI esci Rx Tx V BAT LIN Bit coding: Low = dominant High = Recessive, via pull up resistor GND Bus level compliant to ISO9141. Diagnostic bus, K line synch break synch fieldidentifier field 13 bit (min) 1 byte 1 byte data fields 2, 4, or 8 bytes 1 byte check field response space data fields 2, 4, or 8 bytes 50

52 FlexRay protocol Why Flexray: Need for higher speed (10Mb/s), safer and more predictable communication to allow X by wire systems Application examples: steer by wire brake by wire When: foreseen from FlexRay consortium: Define the protocol, physical layer, conformance specifications etc Electrical braking system Front right Pedal node Rear right Rear left 51

53 Rear right Protocol overview Front left Pedal node Rear left Deterministic data transmission, guaranteed message latency time. No arbitration. Fault tolerant, synchronized global time Redundant transmission channels 52

54 Bibliographie Standards internationaux: ISO7637, automotive transient specification ISO11898, CAN specification LIN protocol specification Quelques sites: Bus de communication: LIN and CAN CRC, Checksum, parity:

55