A literature survey on automotive embedded systems

1. AN AUTOMOTIVE SURVEY
Manu S Ravindra, Colorado State University

2. AUTOMOTIVE ELECTRONICS
•
What is it ?
Kommandogerat – BMW 801 Radial engine series
Radial engine

3. CONTEMPORARY ECU TRENDS
•
Around 80 to 100 in a an automobile

4. ENGINE CONTROL UNIT
•
A typical modern example

5. STEER-BY-WIRE (SBW) SYSTEMS – AN EXAMPLE
•
Power steering

6. 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.

7. 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)

8. SYSTEM MODEL
•
N1, N2 and N3 are nodes.
•
Controller Host Interface (CHI)
•
CPU

9. 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.

10. A SCHEDULING EXAMPLE
•
Τ1 and T6 are SCS scheduled tasks.
•
The rest of the tasks are FPS tasks.

11. A TYPICAL FLEX-FRAME

12. 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

13. 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.

14. 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.

15. NODE CLOCK CORRECTION
•
Measure clock delay.
•
Determine clock correction term.
•
Apply clock correction term (clock rate correction/clock state correction/both).

16. AN OVERVIEW OF THE EVOLUTION

17. WHY FLEXRAY ? FAULT TOLERANCE
•
Topological Flexibility.
•
Synchronous Clock.
•
Conceptual separation.

18. MODERN ELECTRONIC CONTROL UNITS
•
Energy was considered to be “freely available” until now.
•
Energy consumption is directly related to CO 2 emmission of the vehicle.
E/E Architecture
-
Partial networking.
-
AUTOSAR.

19. 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!

20. POWER AND ENERGY EFFICIENCY
 Optimize energy consumption of electronic components.
 Use of networking policies to save power and energy policies. (Communication Energy)

21. COMMUNICATION ENERGY
•
Sub-networking.
•
A “sleep” and “wake-up” object.

22. 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.

23. 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.

24. 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.

25. MULTI-CORE MCU‟S
•
Homogeneous and Heterogeneous multi-core MCU‟s.
•
Multicore benefits.
-
Redundancy
-
Monitoring
•
Code segregation
Dedicated use of cores
Non-volatile Memory

26. THANK YOU