Transcript
Time Triggered Protocol (TTP/C): A Safety-Critical System Protocol Literature Review EE382c Fall 1999
Howard Curtis Global Technology Services MCC
Robert France Global Software Division Motorola, Inc.
The Evolution of Automotive Electronics
• Button Rectifiers
• Unleaded Gas
• Engine Control
• Positive Crankcase Ventilation
• 2 & 3-Way Catalytic Converters
• Fuel Injection
• Power Steering
• Fuel Mix Sensors • MPU’s
• Reformulating Gas • High speed MCU for realtime control • Cold Start • Onboard Diagnostic level 2 • Valve timing control • Airbags • Electric power steering • Adaptive cruise control • ABS with traction control and vehicle stability • First available EVs and hybrids
Source: Motorola, 1999 +&XUWLV5)UDQFH
Automotive Electronics Market Development Automotive Semiconductor TAM World-Wide [$B] 40 35 30 25 20
Electronics and electromechanics (‘Mechatronics’) are replacing hydraulic and mechanical components in vehicles.
5th Wave (EPAS, X-by-Wire, 42V…) ITS (Navigation, Telematics) Body (Comfort, Light…) Safety (ABS, Airbag…) Powertrain
The role of the driver will (gradually) change from machine operator to supervisor of a transportation system.
15 10 5 0 1975
1980
1985
1990
1995
2000
2005
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2010
Total Connectivity in the Vehicle Body (Comfort, Safety, Lighting, Instrumentation)
Driver Powertrain Information Vehicle Systems Dynamics
CAN-B Dashboard Left Door Module Right Door Module
Lighting Control
Control Panel Seat Positioner
Light Level Regulation
Sun-Roof Stepper Motor
Climate Panel Seat Heating
CAN-C
Wiper Wish-Wash
Remote Keyless Entry
Stand-By Heating
Sub Bus DC Motor
Air Bag
Sensor
Squib
Central ECU & Gateway ITS-Bus / MOST
Sub Bus
Climate Control
Video/ Radar Processing
HVAC/ Aux Gauges Multi-use Display Cellular
Telematics
Navigation
CD/DVD
HiFi Radio/ Audio
TV-Tuner
Video Monitor
ISO 9141
Cameras Engine Control Gear Box Control
High Speed Solenoid Network Radar
Vehicle Dynamics TTP
Brake Petal TTP
Electric Brake
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TTP
Steering
Event-Triggered vs Time-Triggered Systems •
Event-triggered systems react to events – Reception of a message – Termination of a task – External interrupt
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Time-triggered systems derive actions from the progression of a globally synchronized time base – Transmission of messages – Task execution – Monitoring of external states
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Time-Triggered Protocols • •
TTP: Family of TDMA based, fault tolerant protocols.
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The development of TTP and TTP/C has been led by Prof. Hermann Kopetz, Technical University of Vienna.
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The commercial development of TTP/C tools and products is led by TTTech.
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Existing protocols J1850 and CAN meet the the bandwidth specification for an SAE Class C protocol, but not the fault tolerant requirements.
TTP/C: A communication protocol specifically designed for safety-related automotive applications.
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TTP/C Node Architecture •
Host – The Host runs the application software.
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Controller Network Interface (CNI) – De-couples the applications-level software from the network using dual ported RAM. – Contains the Message Descriptor List (MEDL) controlling bus access.
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TTP/C Communications Controller. – Provides the actual connection between the TTP/C node and the shared network. – “…the TTP/C controller provides guaranteed transmission times with minimal latency, jitter, fault-tolerant clock synchronization, and fast error detection.” (Ross Bannatyne, “Time Triggered Protocol ...,” Wescon 1998, p. 88.)
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Replica Determinant –
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Allows multiple parallel nodes for fault tolerance
Fail Silent –
Enforced by bus guardians. +&XUWLV5)UDQFH
TTP/C Cluster Fault Tolerant Units (FTUs): Groups of actively replicated nodes
Nodes are Smallest Replaceable Units (SRUs)
Host Subsystems FTU 0
FTU 1
Host CPU
Host HostHostCPU CPUCPU
TTP
TTP TTPTTP
FTU 2
HostHost CPUCPU TTPTTP
Communication Subsystem Duplicated broadcast busses Source: Motorola, 1999
Communication Network Interface (CNI): • System partitioning: autonomous TTP controllers, host CPUs • Hides communication subsystem behind memory abstraction • Predictable interface behavior achieves composability +&XUWLV5)UDQFH
TTP/C Communication Properties •
Static Scheduling – Guaranteed delivery times with known variance (jitter).
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Clock Synchronization – All nodes synchronized to within one microsecond each TDMA round.
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Composability – TTP/C nodes are temporally composable as well as functionally composable. This is a key property of being replica determinant.
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Fail Silent – The bus guardians ensure transmission only during the correct timeslot, in all cases.
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Membership – Every node’s membership is available during each TDMA round.
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TTP/C Bus Access Scheme Time Division Multiple Access (TDMA): • Fixed assignment of slots to nodes • Every node periodically transmits in its slot FTU Slot
Bus 1
Bus 0
SRU Slot
A
B
B
B
FTU 1 B
FTU 0 A
B
C
C
FTU 2 B
C
C
D
B
B
B
FTU 1 B
FTU 0 D
B
E
E
t
FTU 2 B
E
E
t
TDMA Round
Message Descriptor List (MEDL): • Static data structure • Message dispatching table Source: Motorola, 1999 +&XUWLV5)UDQFH
X-by-Wire Systems •
Mechanical & hydraulic subsystems controlling safety-related functions are replaced by computer control systems – Examples: brake-by-wire, steer-by-wire, vehicle dynamics control, active suspension
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Advantages: Cost reduction, weight reduction, easier design, assembly and maintenance, passenger safety and comfort
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Safety-critical applications require: – Fault tolerance: no single fault may lead to a system failure – Predictable and timely system behavior – Synchronized time base (global time)
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Evolution of Steering Systems Electric Power Assist (Newest Technology)
Hydraulic Power Assist (Conventional Steering)
Cooling (high end)
reservoir Servo actuator
Torque sensor To MUX network
hoses
EPS Motor Hydraulic pump
Control unit
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Steer By Wire Systems Steering TTP/C TTP/C Control Comms Comms Unit with Redundant ECU ECU ECUs Triple TTP/C TTP/C TTP/C Redundant Comms Comms Comms Actuators and Control Control Control And And Controllers And Motor
Motor
TTP/C TTP/C TTP/C Comms Comms Comms Sensor Sensor Sensor
Motor
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Modeling & Simulation in Automotive Design Trigger, Crank Angle based
Matlab/Simulink Control Algorithm
Crank Angle Source
PWM frequency
pre-Driver Signal Conditioning Power Module Thermal Behavior
Electro Mechanical Valve
Engine Data, Combustion Chamber Back Pressure
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Simulation Results Open / Close
Valve Speed Coil Current Crank Angle
Cylinder Back Pressure Force Position
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Summary & Conclusions •
Safety critical systems are the next big development area in the automotive industry.
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TTP/C provides the basic features needed for implementing safety critical systems.
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Modeling and Simulation are increasingly important to designing highly complex, safety critical systems affordably.
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Proposed project to implement a partial high level model of TTP/C in Ptolemy as proof of concept.
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Prof. Hermann Kopetz lecturing at UT, Nov. 18.
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