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A literature survey on automotive embedded systems
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Manu S Ravindra, Colorado State University
AN AUTOMOTIVE SURVEY
AUTOMOTIVE ELECTRONICS• What is it ?
Kommandogerat – BMW 801 Radial engine series Radial engine
CONTEMPORARY ECU TRENDS• Around 80 to 100 in a an automobile
ENGINE CONTROL UNIT• A typical modern example
STEER-BY-WIRE (SBW) SYSTEMS – AN EXAMPLE• Power steering
COMMUNICATION BETWEEN ECU’S• Standard communication protocols are used.
CAN (Controller Area Network)
LIN (Local Interconnect Network)
MOST (Media Oriented Systems Transport) are a few examples.
FLEXRAY – THE FUTURE• A hybrid protocol
Time Triggered (TT) messages and Event Triggered (ET) messages
• Consists of two segments – Static segment (ST) and Dynamic segment (DYN)
• Uses TDMA for communication (Time Division Multiple Access)
SYSTEM MODEL• N1, N2 and N3 are nodes.
• Controller Host Interface (CHI)
• CPU
SYSTEM ARCHITECTURE• Implemented by two schedulers.
• Static Cyclic Scheduler
--- non-preempt tasks.
--- start time is decided at the design time or “off-line”.
• Fixed Priority Scheduler
--- preempt tasks.
--- scheduled based priorities.
A SCHEDULING EXAMPLE• Τ1 and T6 are SCS scheduled tasks.
• The rest of the tasks are FPS tasks.
A TYPICAL FLEX-FRAME
THE PROTOCOL• Communication occurs in periodic cycles
• Each cycle consists of two intervals – ST and DYN intervals
• ST and DYN segment lengths can be different but are fixed over the cycles.
• Symbol Window and a network idle timer.
• Frame Identifier
PAYLOAD SEGMENT• Slot counters – Static and Dynamic
• Dynamic mini-slot counters
• Node with frame identifier equal to the current slot counter is allowed to communicate.
CLOCK SYNCHRONIZATION• Backbone of FlexRay operation.
• Clock system in a distributed system would be subject to “clock-drift”.
• Clock drift is an inevitable inherent delay in the arrival of clock from one point to another.
• But a global clock reference is needed to keep track of time.
• FlexRay uses ‘micro-ticks” and “macro-ticks”.
• “Cluster time” is used as a reference of global clock.
NODE CLOCK CORRECTION• Measure clock delay.
• Determine clock correction term.
• Apply clock correction term (clock rate correction/clock state correction/both).
AN OVERVIEW OF THE EVOLUTION
WHY FLEXRAY ? FAULT TOLERANCE• Topological Flexibility.
• Synchronous Clock.
• Conceptual separation.
MODERN ELECTRONIC CONTROL UNITS• Energy was considered to be “freely available” until now.
• Energy consumption is directly related to CO2 emmission of the vehicle.
E/E Architecture
- Partial networking.
- AUTOSAR.
AUTOSAR (AUTOMOTIVE OPEN SYSTEM ARCHITECTURE)• An awesome group of companies working towards delivering the best on production lines
to the world!
• Similar to the SAE (Society of Automotive Engineers) – Another awesome group. The biggest!
POWER AND ENERGY EFFICIENCY Optimize energy consumption of electronic components.
Use of networking policies to save power and energy policies. (Communication Energy)
COMMUNICATION ENERGY• Sub-networking.
• A “sleep” and “wake-up” object.
CAN – CONTROLLER AREA NETWORK• CSMA – Carrier Sense Multiple Access
• Speeds up to 1 Mbps are achievable.
• Bus topology.
• Nothing specific in the protocol to put a node to sleep / turn-off.
• A “sleeping” node “wakes up” if there is any activity on the bus.
• CAN sleep object is a random sleep object.
FLEXRAY • TDMA – Time Division Multiple Access.
• Speeds up to 10 Mbps are achievable.
• Sleep object same as CAN.
• Wake up is performed by sending out a specific symbol.
LIN – LOCAL INTERCONNECT NETWORK• Connects sensors and actuators.
• One wire communication protocol.
• Speeds up to 20kbps.
• Master slave network is employed. One way communication. One master controls one or more slaves. Therefore there is no need for conflict avoidance / collision.
MULTI-CORE MCU’S• Homogeneous and Heterogeneous multi-core MCU’s.
• Multicore benefits.
- Code segregation
- Redundancy
- Monitoring
- Dedicated use of cores
• Non-volatile Memory
THANK YOU
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