Time triggered real time communication Presentation overview - PDF document

Roger Johansson/ 2011 Time triggered real time communication Presentation overview  Background automotive electronics, an application area for time triggered communication.  Time triggered protocols TTPC, first commercial implementation. Originally from TU Vienna. Operational in civil aircrafts. TTCAN, based on Controller Area Network (CAN) which is widely used in today's vehicular electronic systems. FlexRay , based on BMW’s “ByteFlight”. Anticipated in next generation automotive electronic systems.  Hybrid scheduling combining static scheduling with fixed priority scheduling analysis. Time triggered real time communication 1 Roger Johansson/ 2011 A premium passenger car is controlled and managed by 80+ Embedded Systems Infotainment: Comfort Electronics: Telematics Solutions Thermal Management Car PC Chassis Control Wireless Connectivity Parking Assistant Car-to-car communication Floating Car Data Powertrain: Safety: Engine Management Predictive Safety Systems Transmission Control Driver Assistance Systems Power Management Adaptive Cruise Control Electric Power Steering Courtesy of Daimler, Bosch Time triggered real time communication 2

Roger Johansson/ 2011 Virtual differentiation between variants Entertainment configuration Variant 1 A  All variants of a specific model are physically identical and differ only in Motor configuration their individual software A configuration Entertainment  The various included configuration physical components can be F activated or deactivated by Motor the software configuration B Variant 2 Time triggered real time communication 3 Roger Johansson/ 2011 Electrical system 1927-1997 54 54 1200 1200 No. of No. of meters of meters of No. of fuses electric electric wires wires 27 27 575 575 16 16 Wiring diagram, Volvo ÖV4 (“Jacob”) 1927 283 283 9 9 7 7 183 183 5 5 83 83 4 4 50 50 30 30 1927 1927 1944 1944 1956 1956 1966 1966 1975 1975 1982 1982 1997 1997 Time triggered real time communication 4

Roger Johansson/ 2011 The evolution of the electrical system Features Power production and distribution 450 Architecture Simple Optimisation on many 400 components levels 350 Standardised interfaces 300 # of More complex functions 250 functions stand-alone systems 200 ABS, Airbag 150 # of 100 Integration of systems integrated functions 50 Optimisation of information Common data busses 0 1930 1940 1950 1960 1970 1980 1990 1995 2000 2005 1970 1980 1990 2000 2010 Time triggered real time communication 5 Roger Johansson/ 2011 Automotive electronics roadmap Time triggered real time communication 6

Roger Johansson/ 2011 An electrical system… Mirror Lock Lock Window Lift Universal Light Light CAN Seat Htng Instruments Htng Wiper Power Train Central WHtg Interior Roof Body Ctrl ITS Light Trunk Htng Climate x6 Seat Light Seat Htng CAN St-Wheel Panel Universal Motor Lock Lock Sub-Bus Universal Panel Mirror Time triggered real time communication 7 Roger Johansson/ 2011 Multiplex Networks Conventional Network Data Identifier Control Command system Engine Control Module Driver Information Control units Automatic Transmission Central Module Time triggered real time communication 8

Roger Johansson/ 2011 By-wire control Electronic information carrier Hydraulic information carrier The F-8 Digital Fly-By-Wire (DFBW) flight research project validated the principal concepts of all-electric flight control systems now used on nearly all modern high-performance aircraft and on military and civilian transports. The first flight of the 13-year project was on May 25, 1972. Courtesy of Dryden Flight Research Center Time triggered real time communication 9 Roger Johansson/ 2011 Electronics in distributed control ((( ))) ((( ))) traffic control traffic control train (consist) control train (consist) control local control local control ((( ))) ((( ))) wayside control wayside control Time triggered real time communication 10

Roger Johansson/ 2011 Drive-by-wire Time triggered real time communication 11 Roger Johansson/ 2011 Control system implementation strategies Local control  Local information processing  Independent control objects Centralized global control  Local and central information processing  Interconnected control objects Distributed global control  Local and distributed information processing  Interconnected control objects Time triggered real time communication 12

Roger Johansson/ 2011 Non-functional requirements System life Maintainability time Extendability Interoperability Changeability Portability Safety Testability Restructuring Performance/ Usability Efficiency System Security Availability Architecture Robustness Cost-effectiveness Reliability Fault tolerance Produceability Understandability Timeliness Variability (variants, configurations) Conceptual integrity Time triggered real time communication 13 Roger Johansson/ 2011 Tradeoffs from Safety/Reliability requirements The extremes from reliability requirements leads to safety requirements. Safety requirements implies redundancy, (Fail-Operational, Fail-Safe, etc). Safety requirements also demands predictability, we has to show, a priori, that the system will fulfill it’s mission in every surrounding at every time.  In a distributed environment, only time triggered protocols and redundant buses can provide this safety. Contemporary TTP’s are: TTP/C, first commercial implementation. Originally from TU Vienna. Operational in civil aircrafts. TTCAN, based on Controller Area Network (CAN) which is widely used in today's vehicular electronic systems. FlexRay , based on BMW’s “ByteFlight”. Operational in contemporary automotive electronic systems. Time triggered real time communication 14

Roger Johansson/ 2011 TTCAN – Based on the CAN protocol – Bus topology – Media: twisted pair – 1Mbit/s Nod A Node 3 CPU/mem /CC Node 1 Node 6 Node 7 S S S Node 5 Node 4 Node 2 A second controller is required to implement the redundant bus Time triggered real time communication 15 Roger Johansson/ 2011 TTCAN ”Exclusive” – guaranteed service ”Arbitration” – guaranteed service (high ID), best effort (low ID) ”Reserved” – for future expansion... Transmission Columns Basic cycle 0 Basic cycle 1 Basic cycle 2 Basic cycle 3 t Time is global and measured in network time units (NTU’s) Time triggered real time communication 16

Roger Johansson/ 2011 TTP/C – Double channels (one redundant). Bus topology or ”star” (optical) – Media: twisted pair, fibre – 10 Mbit/s for each channel CNI works as a “firewall” Nod Nod Nod Nod 3 Nod Nod Status , global time, membership 1 6 Control , clock interrupt Watchdog , checking consensus Data the actual message Nod Nod Nod Nod Nod Nod 5 4 2 Nod A Nod Nod Nod Nod CPU/mem CNI 1 4 /CC A Nod Nod Nod Nod 2 5 S S S Nod Nod B Nod Nod 3 6 A network is built on either twin buses or twin stars. Time triggered real time communication 17 Roger Johansson/ 2011 TTP/C All communication is statically scheduled Guaranteed service ”TDMA-round” ”message slots” t Non periodical messages has to been fitted into static slots by the application Time triggered real time communication 18

Roger Johansson/ 2011 Flexray – Double channels, bus or star (even mixed). – Media: twisted pair, fibre – 10 Mbit/s for each channel Nod 3 Nod 1 Nod Nod 6 Nod 7 A CPU/mem/ B CC S S A S Nod 5 Nod 4 Nod 2 Redundant channel can be used for an alternative schedule Time triggered real time communication 19 Roger Johansson/ 2011 Flexray ”Static segment” (compare TTCAN ”Exclusive”) – guaranteed service ”Dynamic segment” (compare TTCAN ”Arbitration”) – guaranteed service (high ID), ”best effort” (low ID) 63 62 Network Idle Time Symbol window Guaranteed periodical Guaranteed ”Best-effort” periodical/ aperiodical aperiodical 3 2 1 0 Static segment Dynamic segment (m slots) (n mini-slots) Max 64 nodes on a Flexray network. Time triggered real time communication 20

Roger Johansson/ 2011 Comparisons All protocols targets real time applications. TTCAN and Flexay combines time AND event triggered paradigms well. All protocols are suitable for scheduling tools. TTP/C has commercial production tools. Tools for TTCAN and Flexray are anticipated. CAN, many years experiences, a lot of existing applications. Implies migration of existing CAN applications into TTCAN. TTP/C considered as complex. Poor support for asynchronous events. High complexity, lacks second (or multiple) sources. Flexray is the latest initiative. Supported by most automotive suppliers. Time triggered real time communication 21 Roger Johansson/ 2011 Combining time triggering with events: Exam ple of Hybrid scheduling for TTCAN Messages are sorted into three different categories:  Hard real-time, for minimal jitter with guaranteed response time.  Firm real-time, for guaranteed response time, but can tolerate jitter.  Soft real-time, for “best effort” messages. Time triggered real time communication 22