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1、CAN FD Overview,CAN FD 介绍,2/10/2021,1,FD CAN: Motivation (1/2),Bandwidth is limited with CAN Amount of electronics, function and hence data being communicated in modern-day vehicles are constantly increasing Original CAN specification defined in ISO 11898 standard limits the network communication to
2、 a maximum bandwidth of 1 Mbit/s.Bandwidth is also in practice often limited to 40% of max bandwidth (collision) This limitation causes OEM (wanting to continue to use the CAN protocol) to design additional CAN networks into the vehicle in order to transmit the necessary data. Flashing ECU is too sl
3、ow with CAN Large data volume of program to flash ECU requires high bandwidth. Example: In the 4th generation of BMW 7-series 81 Mbyte to flash, in the 5th generation 1GB Conclusion More networks means more complexity and additional wiring Large volume of data to flash and diagnostic are currently t
4、oo slow OEMs are therefore looking for alternative communication means, faster and with larger bandwitdh,2,2/10/2021,Disclosure or duplication without consent is prohibited,2,FD CAN: Motivation (1/2),Example of ECU and function evolution,3,Mercedes Class E: Evolution Nb of ECU and signal. (Source CA
5、N Newsletter),Safety system: Evolution trend (Source “Expanding Automotive Electronics Systems”),2/10/2021,Disclosure or duplication without consent is prohibited,3,Example of flashing time Flashing 1 GB over CAN (500 KB) may take 24 hours Flashing with a faster communication such as Ethernet can re
6、duce the flashing time to 1 hour,FD CAN: Main difference with CAN,CAN FD increases the Bit Rate Arbitration phase: Same as standard CAN, 250kb, 500kb or 1Mb Data phase: More than 1 Mbit possible, up to 8 Mbit CAN FD increases the Payload (amount of data) can support up to 64 Byte of data compared to
7、 8 Byte for CAN,4,2/10/2021,Disclosure or duplication without consent is prohibited,4,Arbitration,Arbitration,Data 1 (8 Byte),Data 2 (8 Byte),Data 3 (8 Byte),Data 4 (8 Byte),Data 5 (8 Byte),Data 6 (8 Byte),Data 7 (8 Byte),Data 8 (8 Byte),Arbitration,Data (8 Byte),Arbitration,Arbitration,Arbitration,
8、Data (8 Byte),Payload transmitted at higher speed,Arbitration transmitted at the same speed,Arbitration transmitted at the same speed,Up to 8 Data (64 Byte),CAN frame,CAN FD frame (Minimum length),CAN FD frame (Maximum length),CAN FD vs CAN: Protocol difference (1/5),CAN frame,2/10/2021,Disclosure o
9、r duplication without consent is prohibited,5,Bus Idle 3 Bits,Arbitration Field 11 +1 Bit 29 + 1 Bit,Control Field 6 Bit,Data Field 0 to 64 Bit,CRC Field 15 Bit,Start Of Frame 1 Bit,DEL 1 Bit,ACK 2 Bit,End Of Frame 7 Bits,Bus Idle 3 Bits,First Bit Transmitted: Single Dominant Bit,11 Bit: Identifier
10、Field + RTR bit 29 Bit: Base identifier Field + SRR + IDE + Identifier extension + RTR bit Identifier: Unique frame ID RTR: Remote Transmission request SRR: Substitute RTR bit for 29 Bit ID IDE: 1-Bit extension flag,RTR 1 Bit,IDE 1 Bit,Extended Identifier 18 Bit,Identifier 11 Bit,Identifier 11 Bit,S
11、RR 1 Bit,RTR 1 Bit,IDE 1 Bit,r 1 Bit,DLC 4 Bit,Standard format Extended format IDE: Identifier Length (11 bit or 29 bit) R: Reserved DLC: Data Length Code (0000 to 1000,r0 1 Bit,r1 1 Bit,DLC 4 Bit,Data 1,Data 2,Data 8,Up to 8 data field are allowed,Cyclic Redundancy Check,Acknowledgment: Every CAN n
12、ode that receives an error-free transfer must send a dominant bit during ACK. If No node receives the frame properly, the ACK remains recessive,Bit 1-6: If a dominant level occurs: An error is detected by transmitter and receiver. The frame must be sent again Bit 7: If a dominant level occurs: The f
13、rame is valid for the Receiver but not for the transmitter. The frame must be sent again,1,2,3,4,5,6,7,CAN FD vs CAN: Protocol difference (2/5),Start of frame Same bit dominant Arbitration field Same addressing for standard and extended format CAN FD removes the RTR bit and always maintains a domina
14、nt bit (Reserved 1),2/10/2021,Disclosure or duplication without consent is prohibited,6,Difference,CAN,CAN FD,CAN FD vs CAN: Protocol difference (3/5),Control Field: CAN FD has 3 additional bits EDL: Extended Data Length Determines if CAN (dominant) or CAN FD (recessive) BRS: Bit Rate Switch Separat
15、es arbitration phase from Data phase in CAN FD Clock rate switches when BRS is recessive ESI: Error State Indicator (error active/passive) For DLC, same format but length can be 8 Byte 1000: 8 Byte 1001: 12 Byte 1010: 16 Byte 1011: 20 Byte 1100: 24 Byte 1101: 32 Byte 1110: 48 Byte 1111: 64 Byte,2/10
16、/2021,Disclosure or duplication without consent is prohibited,7,Additional bits,CAN FD vs CAN: Protocol difference (4/5),Data field In CAN FD, can be extended to 64 Byte instead of 8 Bytes for CAN CRC field: 15 Bits for CAN 17 bit on CAN FD if data field 16 Byte 21 bit on CAN FD if data field 16 Byt
17、e In CAN FD, previous Stuff bits are included in the CRC calculation, not included in CAN In CAN FD, a CRC delimiter bit is used,2/10/2021,Disclosure or duplication without consent is prohibited,8,CAN FD vs CAN: Protocol difference (5/5),ACK field Sent after the CRC delimiter bit An additional ACK d
18、elimiter id used End of frame Same as CAN,2/10/2021,Disclosure or duplication without consent is prohibited,9,FD CAN: Data rate compared to other bus,Data rate is important for diagnostic and flashing CAN FD offers a faster speed than CAN. 4 times higher bandwidth is realistic (See example) CAN FD o
19、ffer less bandwidth than FlexRay but has a higher data rate, which is interesting to reduce the flashing time. Example (Source GM) 500 Kb/s CAN: Time to transmit 4 CAN message with 8 byte (15% bit stuffing): 1021 sec 2 Mb/s CAN FD: Time to transmit 1 CAN FD message with 32 byte (15% bit stuffing): 2
20、29 sec,10,2/10/2021,Disclosure or duplication without consent is prohibited,10,FD CAN: Cost compared to other bus,A number of alternative to CAN with higher bandwidth already exist However, these networks, like FlexRay and automotive Ethernet, are significantly different from the CAN physical layer,
21、 which means that making a change to support them instead of CAN is very expensive for the suppliers and OEMs. Suppliers like Bosch estimated the cost of CAN FD to be similar to CAN. (Source Bosch 2012 Vector Congress). Controller, transceiver, crystal, cable, etc. similar to CAN,11,2/10/2021,Disclo
22、sure or duplication without consent is prohibited,11,FD CAN: Implementation,CAN FD provides a migration path compatible with CAN CAN 2.0 nodes and CAN FD nodes can communicate with each other as long as the CAN FD frame is not used CAN FD standard exists Defined in ISO 11898-2016 In AUTOSAR v 4.1 CA
23、N FD components are available Transceiver e.g. Infineon, NXP, ST, etc. Next generation ECU will support CAN FD (Source Bosch) CAN FD tools are available Vector, ETAS, etc. Some OEMs plan to bring cars with CAN FD on the roads not later than 2020. General Motors, Daimler, and Volkswagen are ahead. Ot
24、hers such as PSA and Renault will follow. It is unknown when Hyundai and Toyota will equip their vehicles with CAN FD, but according to rumors it will happen around 2020. (Source CAN-newsletter.org),12,2/10/2021,Disclosure or duplication without consent is prohibited,12,FD CAN: Conclusion,A larger b
25、andwidth is necessary to help OEM achieve advance function and flash ECUs, a number of protocol are available, OEM needs to choose the most appropriate CAN FD is based on the CAN protocol and has: Higher bandwidth: Enables to transmit more data and reduce the flashing time Longer payload: Enables to
26、 transmit larger message CAN FD does not have the safety (deterministic) aspect of FlexRay but improves the bandwidth and flashing time compared to CAN CAN FD protocol is very similar to CAN making it “easier” and less expensive than other protocols, however Higher bit rate than CAN involves hardwar
27、e (transceiver) change Larger payload would also involve software modification. Difference in implementation e.g. CRC and message counter for longer data, security module etc. may occurs High interest from OEM to this technology, some of then already plan to have car on the road with this protocol,13,2/10/2021,Disclosure or duplication without consent is prohibited,13,