CAN-FD Flexible Data Rate CAN

Transcription

1 FD CAN-FD Flexible Data Rate CAN A Short Primer and Update V

2 Agenda > Why CAN-FD? What is CAN-FD? Basic Concepts CAN-FD Specifics Data Frame Operating Modes/States Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 3

3 Why CAN-FD? CAN networks reached practical maximums of data transfer Many CAN buses have reached 50%-95%+ bus load level CAN messages contain 50% overhead Standard CAN ~ 29 bits/message for 64 bits of data* Extended CAN ~ 54 bits/message for 64 bits of data* At most, only ~40-50% of the bandwidth is used to exchange useful data Current CAN bus speeds Mbit/sec Limited by physical characteristics of in-vehicle wiring Most auto networks 500Kbit/sec J939 networks = 250Kbit/sec (500Kb/sec under consideration) * - excluding stuff bits Slide: 4

4 Why CAN-FD? CAN bus speed also limited due to the In-Frame Response (IFR) mechanism ACK generation delay in CAN controller + Propagation delay through the transceiver + Propagation delay over wire bit time Other protocols have much higher data throughput rate Ethernet UDP ~64K bytes/datagram, 64 bytes overhead (ipv4) FlexRay 254 bytes/frame, 8 bytes of overhead Slide: 5

5 Agenda Why CAN-FD? > What is CAN-FD? Basic Concepts CAN-FD Specifics Data Frame Operating Modes/States Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 6

6 What is CAN-FD? New network protocol: CAN-FD is a serial communications protocol similar to and compatible with ISO 898- Will be folded into the ISO 898- standard Designed to be a higher bandwidth network compatible with CAN Supports dual bit rates within a message Arbitration-Phase same bit rate as standard CAN Data-Phase integral submultiple of controller clock rate Supports larger data lengths than standard CAN Offers increased data transmission efficiency Transmit/receive up to 64 bytes/message Slide: 7

7 What is CAN-FD? Differences from CAN are limited to CAN-FD controller hardware Existing CAN transceivers usable to 2-8 Mbit/sec Component re-qualification unnecessary Legacy SW usable Data fields up to 8 bytes in length System cost similar to standard CAN Controller, crystal, transceiver, node interconnection cost Crystal requires tighter tolerance when BitRate DATA /BitRate ARB > 6 Progressively introduce CAN-FD nodes into standard networks First commercial silicon to be available at end of 202 Dual rate clock, data fields 8 bytes Slide: 8

8 Agenda Why CAN-FD? What is CAN-FD? > Basic Concepts CAN-FD Specifics Data Frame Operating Modes/States Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 9

9 Basic Concepts CAN-FD is similar to standard CAN and can be configured to fit transparently into an existing CAN network All of the advantages of CAN are available in CAN-FD Message prioritization, guaranteed latency times, flexible configuration, multi-master, multicast capability, error detection & signaling, automatic retransmission on error Tools have been modified to work with CAN-FD Tool infrastructure remains similar to CAN minimizing learning curve CANalyzer/CANoe upgrade released (Ver. 8.0 SP3) Database tools have been modified as well Physical layer is similar Additional consideration must be given to topology when using higher data rates Slide: 0

10 Basic Concepts Summary: CAN-FD is superset of CAN that: Maintains CAN arbitration scheme Maintains ACK scheme Has mode that conforms with CAN 2.0/ISO898- And adds: Higher data bit rates Larger data fields (up to 64 bytes) Larger CRC polynomials to handle larger data fields Maintains compatibility with physical layer of standard CAN Slide:

11 Agenda Why CAN-FD? What is CAN-FD? Basic Concepts > CAN-FD Specifics Data Frame Operating Modes/States Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 2

12 CAN-FD Specifics Messages: Fixed format - similar to standard or enhanced CAN Message length is longer, but still finite Standard CAN-FD ~ 58 bits/message for 52 bits of data* Extended CAN-FD ~ 606 bits/message for 52 bits of data* At a given bus load ~85-88% of the bandwidth is used to exchange useful data Assuming arbitration bits and data bits transmitted at same rate Bandwidth will increase when using higher data rates *- excluding stuff bits Slide: 3

13 CAN-FD Specifics Messages: Increasing data rate also increases effective message rate Standard CAN message with: 4X Data phase ~ 2.2x increase* 8X Data phase ~ 2.5x increase* A mb/sec CAN-FD bus with 8Mb/sec data rate has a data transmission capability similar to a half speed, single channel FlexRay implementation *- calculated using bit identifier and 8 byte data field excluding stuff bits scales linearly Slide: 4

14 SOF r IDE EDL r0 BRS ESI CRC Delimiter ACK ACK Delimiter SOF RTR r r0 CRC Delimiter ACK ACK Delimiter CAN-FD Specifics CAN Base Data frame* Identifier DLC Data CRC EOF IFS CAN-FD Base Data Frame* Identifier DLC Data CRC EOF IFS / * - Excludes stuff bits Slide: 6

15 SOF SRR IDE r EDL r0 BRS ESI CRC Delimiter ACK ACK Delimiter SOF SRR IDE RTR r r0 CRC Delimiter ACK ACK Delimiter CAN-FD Specifics CAN Extended Data Frame* Identifier Extended r0 r DLC Data CRC EOF IFS Identifier CAN-FD Extended Data Frame* Identifier Extended DLC Data CRC EOF IFS Identifier / * - Excludes stuff bits Slide: 7

16 Agenda Why CAN-FD? What is CAN-FD? Basic Concepts CAN-FD Specifics > Data Frame Operating Modes/States Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 22

17 SOF r IDE EDL r0 BRS ESI CRC Delimiter ACK ACK Delimiter Data Frame Data Frame: Data frames are used to transmit data on the CAN-FD bus Consist of two phases Arbitration and Data CAN-FD Base Data Frame* Identifier DLC Data CRC EOF IFS / Arbitration Phase (fixed data rate) Data Phase (flexible data rate) Arbitration Phase (fixed data rate) * - Excludes stuff bits Slide: 23

18 SOF r IDE EDL r0 BRS ESI CRC Delimiter ACK ACK Delimiter Data Frame Data Frame: and seven different bit fields SOF, Arbitration, Control, Data, CRC, ACK, EOF CAN-FD Base Data Frame* Identifier DLC Data CRC EOF IFS / Start Arbitration Control Data Field CRC ACK End Of Field Field Field Field Of Frame Frame * - Excludes stuff bits Slide: 24

19 SOF r IDE EDL r0 BRS ESI SOF RTR r r0 Data Frame Start of Frame CAN and CAN-FD use the same SOF a single dominant bit Recessive CAN Base Data frame Identifier DLC Data Bit state Dominant Recessive CAN-FD Base Data frame Identifier DLC Data Bit state Dominant Slide: 25

20 SOF r IDE EDL r0 BRS ESI SOF RTR r r0 Data Frame Arbitration Field Little difference between CAN and CAN-FD arbitration fields Both share the same addressing for Base and Extended formats CAN-FD removes the RTR bit and maintains an always dominant r bit Identifier DLC Data CAN Base Data frame Identifier DLC Data CAN-FD Base Data frame Slide: 26

21 SOF r IDE EDL r0 BRS ESI Data Frame Control Field: CAN and CAN-FD share the following bits: IDE, r0 and the DLC bits Identifier DLC Data CAN-FD adds the following bits to the control field : EDL Extended Data Length Determines if CAN or CAN-FD BRS Bit Rate Switch Separates Arbitration phase from Data phase in CAN-FD Clock rate switches to Data phase clock at this point ESI Error State Indicator Slide: 27

22 SOF r IDE EDL r0 BRS ESI CRC Delimiter ACK ACK Delimiter Data Frame Control Field: Data Length Code (DLC) 4 bits used for both formats CAN-FD compatible with CAN at data lengths 7 CAN ignores 3 lsb if DLC = 8, CAN-FD does not For lengths 8, CAN-FD uses the following DLCs: 000 = 8 00 = = 2 0 = = 6 0 = 48 0 = 20 = 64 Identifier DLC Data CRC EOF IFS 0-8, 2, 6, 20, 24 32, 48, or 64 bytes / Slide: 28

23 SOF r IDE EDL r0 BRS ESI CRC Delimiter ACK ACK Delimiter Data Frame Data Field: 0-8 bytes in CAN 0-8, 2, 6, 20, 24, 32, 48, or 64 bytes in CAN-FD Bytes are transferred msb first No data field if DLC = 0 Identifier DLC Data CRC EOF IFS 0-8, 2, 6, 20, 24 32, 48, or 64 bytes / Slide: 29

24 CRC Delimiter ACK ACK Delimiter Data Frame CRC Field: Data CRC EOF IFS / Size of CRC differs based on CAN/CAN-FD and length of DLC 5 bits for CAN 7 bits for CAN-FD where data field 6 bytes 2 bits for CAN-FD where data field > 6 bytes Preceding stuff bits are included in the CAN-FD CRC calculation CAN does not use stuff bits in the CRC calculation CAN-FD CRC delimiter transmitted as bit, but due to phase shift, etc. receiver can accept delimiter of up to 2 bit times Data Phase of CAN-FD frame ends with the sample point of the first bit of the CRC delimiter Slide: 30

25 CRC Delimiter ACK ACK Delimiter Data Frame ACK Field: Data CRC EOF IFS / ACK sent at the end of first CRC delimiter bit Slight difference in the format between CAN and CAN-FD CAN-FD recognizes up to two bit times as a valid ACK bit extra bit time allowed to compensate for transceiver phase shift and bus propagation delay due to the switch from a high data phase clock to a low arbitration phase clock End of Frame: Both Data Frames and Remote Frames are delimited by a group of 7 recessive bits Slide: 3

26 Data Frame CAN-FD Oscilloscope Trace: Arbitration Phase Data Phase Arbitration Phase Slide: 32

27 Agenda Why CAN-FD? What is CAN-FD? Basic Concepts CAN-FD Specifics Data Frame > Operating Modes/States Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 36

28 Operating Modes/States CAN-FD controller has three operating modes: Normal Mode Full functionality Bus Monitoring Mode Controller receives data from the bus, but only sends recessive bits Cannot initiate message transmission Can reroute dominant bits internally if necessary Restricted Operation Mode Controller can receive and transmit Data Frames and Remote Frames Acknowledges valid frames Cannot send Active Error Frames or Overload Frames Waits for Bus Idle to re-sync with bus Slide: 37

29 Operating Modes/States and four operating states: Integrating After starting or during bus-off recovery Controller waits until it detects consecutive recessive bits Switches to Idle mode Idle If ready for Start-of-Frame Switches to either Receiver or Transmitter mode Receiver Receives data if active bus detected and is not transmitting Transmitter When originating a message, and does not change until bus is idle Slide: 38

30 Agenda Why CAN-FD? What is CAN-FD? Basic Concepts CAN-FD Specifics Data Frame Operating Modes/States > Physical Layer Considerations Summary References FAQ Vector s Roadmap for CAN FD Slide: 39

31 Physical Layer Considerations Bus topology is also is a determining factor Linear bus configuration highest speed Lowest overall capacitance = highest frequency Short stubs add little to overall distributed capacitance Terminated, balanced line minimizes radiated EMI Slide: 4

32 Physical Layer Considerations Linear configuration with star terminations Approx ½ speed of linear bus Node A Node D Node B Node E Node C 20 Ω 5% - /4W Termination Resistors Node F Large lumped capacitance on each end Increased EMI possibility depending on stub length Slide: 42

33 Physical Layer Considerations Passive star central terminator configuration slowest speeds Approx ¼ speed of linear bus Node A Node D Node B Node E Node C 60Ω 5% - /4W Termination Resistor Node F Increased possibility of reflections due to non-terminated nodes Increased EMI possibility depending on stub length Slide: 43

34 Physical Layer Considerations EMC Considerations Faster bus speeds faster bit rise and fall times e.g. Mb/s rise times ~ nsec. (5 0 MHz) e.g. 0Mb/sec rise times ~ 5-0 nsec. (50-00 MHz) Bus should be designed for the Data Phase frequency, not the Arbitration Phase frequency Harmonic content will be at higher levels at higher frequencies Traditional methods of suppressing undesired harmonics may not work Closer attention to wiring design, routing and connections will be necessary Low capacitance wiring methods recommended Slide: 44

35 Summary Serial communication buses require increased bandwidth CAN-FD can provide this increased bandwidth Increased data rates Increased data payloads CAN-FD is designed to co-exist with CAN on the same network CAN-FD nodes must also meet CAN 2.0/ISO 898- specifications CAN-FD frames can co-exist with CAN frames on a CAN-FD bus CAN 2.0 nodes and CAN-FD nodes can communicate with each other as long as the CAN-FD frame format is not used CAN-FD format allows migration to CAN-FD from CAN CAN-FD nodes on a CAN bus can communicate with external CAN-FD devices as long as the CAN nodes remain in a stand-by state. For example, a CAN-FD node communicating with and external PC as part of a module flash operation Slide: 45

36 References Paper CAN with Flexible Data Rate Florian Hartwich, Robert Bosch GmbH;CAN in Automation, icc 202, March 202 Presentation CAN FD CAN with Flexible Data Rate Florian Hartwich, Robert Bosch, GmbH; Feb. 5, 202 CAN with Flexible Data Rate Specification Version.0 (Released April 7, 202), Robert Bosch, GmbH; April, 202 M_CAN Controller Area Network User s Manual, Revision 2.0., Robert Bosch, GmbH; March 2, 202 Slide: 46

37 FAQ Should we treat CAN FD as a new bus system? CAN FD is a superset of CAN Easy migration from existing CAN systems Tool configuration needs only slight modification e.g. baud rate for data phase Test scripts and DBC databases can be reused for CAN FD payloads up to 8 bytes Which database format should we use for CAN FD? DBC format already supports payloads of 64 bytes Autosar System Description is a standardized alternative Do we need a PDU-abstraction for CAN FD? Probably makes sense for payloads > 32 bytes PDUs also allow additional data protection, e.g. CRC Autosar System Description already supports PDUs Slide: 47

38 FAQ Will CAN FD to have any impact on LIN? CAN FD provides no cost advantage for body applications and is not expected to replace any typical LIN application CAN FD frames with payload > 8 bytes can only use raw TP routing Slide: 48

39 FAQ Will CAN FD to have any impact on FlexRay? CAN FD can be a less expensive alternative to FlexRay and is designed to close the speed gap between CAN and FlexRay FlexRay is better suited for time-triggered applications CAN FD should be used for event-triggered applications requiring a higher data rate More likely, CAN FD and FlexRay will coexist in future vehicle networks Slide: 49

40 FAQ Will CAN FD to replace existing CAN systems? CAN systems with high bus loads (>50%) are good candidates to migrate to CAN FD The higher data rate and payload of CAN FD may help to avoid splitting CAN systems with high bus loads Split CAN networks can be combined into a single CAN FD network in order to avoid gateway latencies For migration purposes it may make sense to mix CAN with CAN FD in a single network Legacy CAN ECUs will require an adapted controller that ignores CAN FD frames It is not yet clear if mixed CAN - CAN FD networks will be common in future vehicles Slide: 50

41 Thank you for your attention. For detailed information about Vector and our products please have a look at: Author: Lotoczky, Rick Vector CANtech, Inc. Slide: 5