Automotive Networks Automotive Networks Dave Olsen
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Automotive NetworksAutomotive NetworksDave Olsen
Automotive Topology
1
Automotive Network
Automotive NetworkIncreasing demand for bandwidth– Increasing demand for bandwidth
– Desire to reduce number of networking technologies• LIN, CAN, FlexRay, MOST
– Distributed System need synchronization
– Guaranteed QOS required
G t d L t i d– Guaranteed Latency required
– 50-70 ECU’s in a modern car
2
Automotive Networks
Current networks– MOSTMOST
• Synchronous TDMA Ring
• 25, 50, 150 Mbps
• Reserved bandwidth• Reserved bandwidth
– CAN• CSMA/CR bus system
• < 1Mbps
• Prioritized by CAN identifier
– FlexRay: • Time-triggered TDMA Bus and/or Star
• < 10 Mbps
• Guaranteed Latencies
3
CAN Messages
8 bytes of data per frame
Base or Extended frame formatBase or Extended frame format– Base: 11 identifier bits
– Extended: 29 identifier bits
Messages prioritized by identifier
Low latency for high priority frames
Possible high latency for low priority frames
Messages are unique per transmitter
Two transmitters attempting to send the same message would cause a bus conflict
Cyclical/Spontaneous messagesy p g
4
Cyclical CAN Traffic
14
Drivetrain CAN
10
12
8
10
sage
Typ
es
4
6
Mes
s
0
2
1 1.25 2 2.5 3.3 5 10 12.5 20 50 83.3 100
5
Packets/Second
1243 Packets/Second
Cyclical CAN Traffic
350000
Drivetrain CAN
250000
300000
200000
250000
s/Se
cond
100000
150000Bit
0
50000
1 1.25 2 2.5 3.3 5 10 12.5 20 50 83.3 100
6
Packets/Second
635955 Bits/Second
Cyclical CAN Traffic
25
Climate Control CAN
20
15
sage
Typ
es
5
10Mes
s
01 1.25 2 2.5 3.3 5 10 12.5 20 50 83.3 100
7
Packets/Second
Cyclical CAN Traffic
120000
Climate Control CAN
80000
100000
60000
80000
Bits
/Sec
ond
20000
40000
01 1.25 2 2.5 3.3 5 10 12.5 20 50 83.3 100
Packets/Second
8
FlexRay
Flexible TopologyBus– Bus
– Star
– Combination Bus/Star
– Redundant
0-254 Data bytes per frame
Synchronized Network Clock
Software TDM
Comm nication C cleCommunication Cycle– Static segment, Dynamic segment, Symbol segment, Network Idle Time
9
FlexRay Frame
10
FlexRay Clock
MicrotickNode’s own internal time base– Node s own internal time base
– Derived from a local oscillator
– Free running, not synchronized with system
Macrotick– Derived from system wide clock sync algorigthm
– Always an integral number of microticks• Number of microticks per macrotick varies from node to node
• Number of microticks per macrotick can vary from macrotick to macrotickp y
Transmission cycles start/end on Macrotick boundries
11
FlexRay Communication Cycles
Communications based on a recurring sequence of 64 communication cycles numbered 0-63y
Static Segment– Present in every cycle, used for time-triggered communications
Dynamic Segment– Optionally present in the communication cycle and is used for ad-hoc,
event-driven communicationevent driven communication
Symbol Window– Optionally present in the communication cycle and is used to transmit
Fl R d fi d b lFlexRay defined symbols
Network Idle Time (NIT)– NIT is used by each node to calculate and apply clock correctionNIT is used by each node to calculate and apply clock correction
12
Communication cycle
13
Sources
http://www.ip-extreme.com/downloads/flexray_mb_wp.pdf
http://www ece cmu edu/ ece649/lectures/21 flexray pdfhttp://www.ece.cmu.edu/~ece649/lectures/21_flexray.pdf
http://www.flexray.com/products/protocol%20overview.pdf
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