CAN To FlexRay Migration Framework

1
CAN To FlexRay Migration Framework

• Richard Murphy
• Automotive Control Group,
• Waterford Institute of Technology
• E-mail richmillions_at_gmail.com

2
Agenda

• Introduction
• Background
• Proposed Solution
• Test Case
• Conclusion

3
Introduction
4
Aims

• To present a method of migrating from CAN to
  FlexRay
• To explain why this would be necessary
• To present issues encountered carrying out a
  practical implementation

5
Background
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Why Migrate?

• Increase in traffic on CAN bus due to increased
  (critical and non-critical) functionality of
  automotive applications
• To avail of features available on the FlexRay
  protocol not available on the CAN protocol
• Bandwidth
• Time-Triggered Event-Triggered
• Redundancy
• Determinism
• Topology

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FlexRay Characteristics

• High Data Rate (10Mbit/s apiece on dual channels)
• Static (ST) and Dynamic (DYN) segments
• Multiple Topologies
• FlexRay Payload - up to 254 Bytes
• Support of wake-up and sleep functionality via
  the bus

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FlexRay Cycles
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FlexRay Frame

• Header
• Frame ID, Payload length, Header CRC, Cycle
  count, Reserve bit, Payload preamble, Null Start
  up sync frame indicators
• Payload Data
• Trailer CRC (Cyclic Redundancy Check)

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Proposed Solution
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Migration Issues

• Cost
• CAN Mature Protocol, FlexRay Relatively New
• FlexRay Complexity-
• 74 Parameters (Eric Armengaud, 2006 )
• CAN purely Event-Triggered, FlexRay both
  Time-Triggered Event-Triggered

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Migration Procedure

• Task Graph Analysis
• Deadline Analysis (ST)
• Response Time Analysis (DYN)

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Static Segment

• Initial Parameters required
• Task graph ri and Di, WCET and task periods
• Redistribute any slack in the system and
  recalculate ri and di values
• Message deadline
• td(mi) di - ri wi
• ST Slot size
• gdstaticSlotsize(payloadi)size(overheadi)/Busspe
  ed

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Payload Definition
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Payload Definition contd

• Heuristically choose payload
• Overhead 14 Bytes
• 5 Bytes Header
• 3 Bytes CRC
• 2 Bytes TSS
• 4 Bytes for clock and Security

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Periodicity Distance Constraints

• Period Constraint Message cycles occur at
  multiple harmonic periods
• Distance Constraint The distance between two
  successive messages must be lt period
• Allows decoupling of application task schedules
  from FlexRay communication schedules

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Dynamic Segment

• Worst Case Response Time Analysis (WCRTA)
• Rm(t)Cmdmwm(t)
• Communication Time per message Cm
• Delay if message is transmitted just after its
  slot has passed dm
• Delay by St bus and higher priority messages wm

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Parameter Calculation

• Cm Fmessagei / Busspeed
• dm FR(t)-(STbus(messageIDi.gdMinislot)NIT)
• wm(t) STbushp(m)(pLatestTx.gdMinislot)NIT

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ACC (Adaptive Cruise Control)Test CASE
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Test Case

• Adaptive Cruise Control configuration

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Parameter Comparison
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FlexRay System Parameters
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Period and Distance Constraint Validated
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Conclusion

• Using this migration procedure it is possible to
  complete a successful migration from an
  application implemented on a CAN system to
  successful implementation on a FlexRay system

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• Thank you for your attention
• Questions?