Enabling Hybrid CAN and CAN FD Networks Tony Adamson Marketing Manager – CAN / LIN / FlexRay NXP Semiconductors COVER PAGE SUBTITLE PLACEHOLDER COMPANY CONFIDENTIAL
Why Automotive OEMs look to CAN FD Accelerate bandwidth in general operation • New and increasingly complex functions being introduced + Consolidation of computing power and increasingly distributed functions Accelerate ECU Flashing in production • ECUs need to be flashed as quick as possible, without EMC constraints Security introduction will require larger payloads • Signatures and encryption will not be feasible / insufficient using validated technologies with 8-bytes (64-bit) frames . CAN FD can address each of these problems – with a lower level of disruption than switching to alternate technologies. 2. October 28, 2015 COMPANY CONFIDENTIAL
Challenges of Introducing CAN FD for General Operation Disclaimer: network implementation choices are ultimately dependent on many factors (# of branches, nodes / branch, cable lengths). Core Problem: CAN FD and “Classic” CAN nodes cannot be mixed, Gateway while not all nodes need bandwidth acceleration Chassis ADAS Power Train TCU CAN FD Gateway Gateway Fast Branch Chassis ADAS Power Train Chassis ADAS Power Train TCU TCU EPS Cl ECU EPS Cl Classic CAN Network ECU EPS Cl ECU - Critical nodes at bandwidth limit (either flashing or general use) Option 1: CAN FD Fast Branch Option 2: Update complete branch - Network organised by function - Networks organised by technology, not function. - Network organised by function - Increased routing via gateway - Legacy nodes updated - Complicated firewall policies - Higher development costs - Lacks scalability - Lack of MCU availability // Higher cost of MCU - Sub-optimal wiring solutions 3. October 28, 2015 COMPANY CONFIDENTIAL
Wish list to introduce CAN FD in General Operation Keep networks organized by function • Gateway • Simpler security implementation • Optimal wiring solution for application Chassis ADAS Power Train Apply CAN FD where bandwidth is critical and • TCU leave legacy nodes untouched • Overcomes / limits challenge on MCU availability • Limits investment costs and any BoM cost increase Classical CAN and CAN FD arbitrating against • each other on the bus Scalable for future network upgrades • EPS Cl ECU • Need CAN FD in an additional node? Upgrade later on. 4. October 28, 2015 COMPANY CONFIDENTIAL
Hybrid Networks for ECU Flashing Use-case Only CAN FD used only when ECUs flashed. Flashed ECU 1 General operation remains Classic CAN. TRX MCU Device flashed @ 2-5-8Mbps, no EMC constraints. 5 Mbps CAN FD Capable Capable External Programmer Flashed ECU 2 MCU TRX CANH CAN FD 5+ Mbps CANL TRX MCU Capable Capable CANH 5 Mbps CAN FD CANL Capable Capable CAN FD Passive function Legacy CAN ECU allows Classic CAN to co-exist: Transceiver set to partial networking mode TRX MCU CANH with FD frame tolerance active during CAN 1 Mbps Classic CANL FD flashing. ECU participates in general Capable CAN operation as standard Classic CAN node PN OFF 5. October 28, 2015 COMPANY CONFIDENTIAL
Limitations of FD Passive for General Operation FD Passive Ideal Solution Transceiver solution, which blocks CAN FD traffic reaching the Transceiver solution, which blocks CAN FD traffic reaching the Classic CAN controller. Classic CAN controller. Extension of partial networking – only active when ECU node is in Available in all power modes. partial networking sleep mode. Requires ECU software support for partial networking and No software changes. network management modes. Available in 14-pin Partial Networking transceivers only. Available in 8-pin and 14-pin variants, with or with out low power and partial networking modes. Requires changes to network management to put all Classic CAN No new network management needed. CAN and CAN FD devices into sleep mode, or to wake up. nodes to arbitrate seamlessly against each other on the bus. Any solution to be fully accepted in the industry must be: • Fully ISO compliant and not violate the rules of CAN (FD). • Be fully interoperable with AUTOSAR . • Ensure no messages are lost and all ECUs always stay in synch with the bus. • Handle all error scenarios on the bus. • Be true drop-in replacement of a standard HS-CAN transceiver. 6. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Overview Legacy CAN ECU FD Shield is drop-in replacement for TRX all types of HS-CAN transceivers. - Basic HS-CAN CAN FD Capable HS-CAN - with Standby Mode Transceiver - with Sleep Mode RXD CANH RXD MCU - with Partial Networking Mode Classic CANL CAN TXD TXD No further hardware changes needed Legacy CAN ECU TRX MCU CANH 1 Mbps Classic CANL Capable CAN 7. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Operation CAN FD CAN FD node 1 node 2 FD Shield Classic CAN Switch to CAN FD node 3 frame format CAN FD node 1 starts transmitting a CAN FD frame ESI TXD SOF ID28 ID27 ID26 ID25 ID24 ID23 ID22 ID21 ID20 ID19 ID18 RRS IDE FDF res BRS CAN FD node 1 RXD TXD CAN FD node 2 RXD classic TXD CAN node 3 RXD FD Shield forces RXD to remain low 8. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Operation CAN FD CAN FD node 1 node 2 FD Shield ISO11898-1: Classic CAN 10.4.4.3 Error delimiter node 3 … After sending an error flag, each node shall send recessive bits and monitors the bus until it detects a recessive bit … ESI TXD FDF res BRS CAN FD node 1 RXD TXD CAN FD node 2 RXD classic TXD CAN Wait for 6 dominant bits = stuff error Error flag (blocked by FD shield) node 3 RXD RXD=recessive! 9. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Operation CAN FD CAN FD node 1 node 2 FD Shield Classic CAN ISO11898-1: node 3 10.4.2.7 ACK field … The ACK delimiter, …, shall be a recessive bit. … 10.4.2.8 EOF … consisting of seven recessive bits forming the EOF . TXD CRC CAN FD 1 bit ACK delimiter + 7 bit end of frame (EOF) delimiter node 1 RXD TXD CAN FD ACK 1 bit ACK delimiter + 7 bit end of frame (EOF) node 2 RXD 10.4.4.3 Error delimiter After sending an error flag, each node … monitors the bus until it detects a recessive bit. Afterwards, it shall start sending seven more recessive bits. classic TXD 1bit recessive + 7 bit error delimiter (ED) CAN node 3 RXD SOF FD shield releases RXD during ACK slot RXD now represents the bus! 10. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Operation CAN FD CAN FD node 1 node 2 FD Shield Classic CAN node 3 TXD CRC CAN FD 1 bit ACK delimiter + 7 bit end of frame (EOF) 3 bit intermission delimiter node 1 RXD TXD CAN FD ACK 1 bit ACK delimiter + 7 bit end of frame (EOF) 3 bit intermission node 2 RXD classic TXD 1bit recessive + 7 bit error delimiter (ED) 3 bit intermission CAN node 3 RXD SOF FD shield releases RXD during ACK slot RXD now represents the bus! 11. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Operation CAN FD CAN FD node 1 node 2 FD Shield All nodes remain constantly synchronized Classic CAN Classic CAN and CAN FD ECUs can node 3 immediately arbitrate to send the next frame No interruption between messages No complicated bit synchronisation TXD CRC CAN FD delimiter node 1 RXD CAN FD TXD ACK node 2 RXD Classic CAN (node 3) starts transmitting a classic CAN frame classic TXD SOF CAN node 3 RXD 12. October 28, 2015 COMPANY CONFIDENTIAL
FD Shield Operation A “Shielded” Classic CAN controller can participate in the general network communications via Classic CAN with CAN FD or any other “Shielded” Classic CAN controllers. Implications: A Classic CAN controller will be error passive most of the time, if the majority of frames are • CAN FD frames. • Receive error counter is increased multiple times with each CAN FD frame. • T ransmit error counter is not affected, thus no risk of entering “bus off”. • Error frames let the CAN FD shield release RXD / TXD immediately. • A “shielded” classic CAN controller participates in the global error scenario and thus stays in synch. • NXP has a specific solution for reporting errors for the Classic CAN controller, when required. Details are given in NXP’s technical report TR1406 . • 13. October 28, 2015 COMPANY CONFIDENTIAL
Industry Support and Validation of FD Shield No ISO conformance issues when using FD Shield technology • • Collaboration with conformance testing house confirming FD Shield’s compliance to all rules of ISO11898-1 and -2. • FD Shield evaluated vs. ISO “CAN FD Tolerant” test specification. • Evaluation of NXP’s FD Shield Technical Paper already confirms no issues! Fully compatible with AUTOSAR specifications v4.2.1 and v4.0.3 • • Vector confirm no issues when operating AUTOSAR in combination with NXP’s FD Shield, and no issues with ERROR_PASSIVE state (is not used by high layers of software). 14. October 28, 2015 COMPANY CONFIDENTIAL
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