Challenges of Implementing Timed Models on Timed Platforms

Transcription

1 Challenges of Implementing Timed Models on Timed Platforms Patricia Derler, Hugo Andrade, Arkadeb Ghosal, Rhishikesh Limaye, Jacob Kornerup, Ankita Prasad, Trung Tran, Kaushik Ravindran Ptolemy Miniconference Oct 16, 2015

2 What we do Measurement and Control Hardware Development Tools System Platforms Graphical software Heterogeneous hardware To build measurement and control systems

3 Application Areas Historically focus on Test and Measurement Acquiring data, instrument control Applications New Application areas Embedded Systems, Cyber-Physical Systems, Internet of Things, With new application areas come new requirements.

4 ftp://ftp.ni.com/pub/branches/asean/140331_lv_brochure_2013.pdf

5 Applications Real-time optical coherent tomography (OCT) imaging system to enable early cancer detection combines 320 simultaneous channels at 10 MS/s, LabVIEW performs >700,000 FFT/sec. European Extremely large telescope (E-ELT) 1.87 teraflops of data, 64 compute notes at 512 cores, and 14,000 samples every 2 ms The Large Hadron Collider (LHC) at CERN requires precise synchronization LabVIEW FPGA serves as the timekeeper for more than 100 collimators, control for approximately 600 stepper motors with millisecond synchronization over the 27 km of the LHC.

6 Challenges Time representation Precision Coercion, rounding Phase alignment LabVIEW timestamp: 128-bit data type that represents absolute time The most significant 64 bits should be interpreted as a 64- bit signed two's complement integer. (number of whole seconds after Epoch 01/01/ :00:00.00 UTC). The least significant 64 bits should be interpreted as a 64-bit unsigned integer. (number of 2-64 seconds after the whole seconds specified in the most significant 64-bits) Jitter Hardware clock Clock edge, clock domain, clock rate Multiple timescales, relation to global/tai time Clock synchronization Programming with time

7 Time in LabVIEW Timing Source 1kHz, 1MHz, software triggered, Create/Clear/Instantiate timing source Create timing source hierarchies Timing Structure Timed Loop Timed Sequence Single Cycle Time Loop (SCTL) Programming with Time Wait until time or tick Measure elapsed time Get current time Create timestamp Get time difference Convert time to value/string and the reverse Format timestamp

8 Programming with Time Configuration: Period Offset Priority Processor Timing Source What to do if timing is not met Configuration for next iteration Runtime status When did the execution actually start How long did the execution actually take

9 LabVIEW Timing Engine Nanosecond engine to keep track of time within a program Interfaces to the OS to manage time Can use a local real-time clock (RTC) or can be driven by an external reference clock integrated through the NI Time Sync Framework (NI- TimeSync) Functions and structures (Wait, Timed Loop) in LabVIEW use the nanosecond engine for time keeping

10 An example: PWM Generation and Current Sampling for Brushless Motor Control SCTL for PWM, requires precise timing time Current Loop Period (50 us) PID PID PID PID Shared Variable for communication While Loop for PID which is difficult to write in SCTL Complex, brittle code

11 LabVIEW Communications

12 Time in NI Hardware FPGA vs RT Processor Synchronization supported for various platforms GPS, IEEE (IEC 61588:2009), PPS or IRIG-B NI EtherCAT RIO deterministic Ethernet-based communication protocol

13 Timing of a Virtual Instrument (VI) Compilation, Clumping LabVIEW VI Clumps: Nodes that can be executed together LabVIEW Execution Systems preemptive, cooperative multithreading schedule execution of clumps in threads nondeterministically Special case: Timed Loop. All code enclosed in a timed loop is executed in a single thread Operating system schedule threads on cores LV Execution System Real-time OS #Threads = #Cores * 4 Priority Levels * 5 Non-UI Execution Systems + 1 UI Execution System

14 Timing of a VI Measured execution time contains VI execution as well as runtime system overhead Timing statistics: Number of runs, average, shortest, longest time spent for diagram, display, draw, tracking, r/w local variables Profile memory usage number of bytes and independent memory blocks used by a VI. However, memory profiling substantially slows down the execution speed.

15 Achieving precise timing behavior with LabVIEW and NI hardware is possible but it is not easy to get it right Now: Future:

16 Research Challenges Time Representation Logical vs. Real time Timing Analysis WCET Mapping functionality onto distributed, heterogeneous hardware Design-space exploration PRET Machines NIST Cyber-Physical Systems Public Working Group, Timing and Synchronization Subgroup Time-Aware Applications, Computers, and Communication Systems (TAACCS) IEEE 802 standards group and the AVnu Alliance Industrial Internet Consortium

17 Date and Time Extensions to Ptolemy II Patricia Derler

18 How does Ptolemy model time? Every director has a local clock that keeps track of model time/simulated time

19 How does Ptolemy model real time? Some directors have a synchronizetorealtime property, others can use the SynchronizeToRealTime attribute 1 time unit corresponds to 1 second The system time at simulation start time is recorded

20 ptolemy.data.type.basetype.datetype

21 Actors to create and handle DateTokens Create DateTokens Modify DateTokens Convert DateTokens Relate model time to real time

22 Relate model time to real time model time

23 Relate model time to real time model time 10/16/2015 4:00pm 10/16/2015 4:05pm real time

24 Relate model time to real time synchronizetorealtime = true model time output the model time value that corresponds to the date 10/16/2015 4:00pm 10/16/2015 4:05pm

25 Relate model time to real time synchronizetorealtime = true model time output the model time value that corresponds to the date output the date token at the specified date 10/16/2015 4:00pm 10/16/2015 4:05pm

26 Relate model time to real time synchronizetorealtime = true model time output the model time value that corresponds to the date output the date token at the specified date output the date at real time corresponding to the model time of the input event 10/16/2015 4:00pm 10/16/2015 4:05pm

27 Thanks