Challenges of Implementing Timed Models on Timed

PlatformsPatricia Derler, Hugo Andrade, Arkadeb Ghosal,

Rhishikesh Limaye, Jacob Kornerup, Ankita Prasad, Trung Tran, Kaushik Ravindran

Ptolemy Miniconference Oct 16, 2015

What we do

• Graphical software • Heterogeneous hardware • To build measurement and control systems

Measurementand Control Hardware

Development Tools System Platforms

Application AreasHistorically focus on Test and Measurement

• Acquiring data, instrument control

New Application areas

• Embedded Systems, Cyber-Physical Systems, Internet of Things, …

Commercial Technology

Models of Computation, User Interface

Math and Analysis

Measurement and Control I/O

Timing

Applications

Deployable Targets

With new application areas come new requirements.

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

ApplicationsReal-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.

https://decibel.ni.com/content/blogs/labview-news-english/2015/04/07/point-of-view-why-you-just-need-time

Challenges

• Time representation • Precision

• Coercion, rounding

• Phase alignment • Jitter • Hardware clock

• Clock edge, clock domain, clock rate

• Multiple timescales, relation to global/TAI time • Clock synchronization • Programming with time

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 01/01/1904 00:00:00.00 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)

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)

• Precise timing, execution feedback, timing characteristics that

• 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

Programming with TimeConfiguration: • Period • Offset • Priority • Processor • Timing Source • What to do if timing

is not met

Runtime status • When did the execution

actually start • How long did the

execution actually take

Configuration for next iteration

executes all functions inside within one tick of the FPGA clock

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

An example: PWM Generation and Current Sampling for Brushless Motor Control

PID PID PID PID

CurrentLoopPeriod(50us)

time

Complex, brittle code

SCTL for PWM, requires precise timing

While Loop for PID which is difficult to write in SCTL

Shared Variable for communication

LabVIEW Communications

Time in NI Hardware

• FPGA vs RT Processor

• Synchronization supported for various platforms • GPS,

• IEEE 1588-2008 (IEC 61588:2009),

• PPS or

• IRIG-B

• NI EtherCAT RIO • deterministic Ethernet-based communication protocol

Real-time OS

LV Execution System

Timing of a Virtual Instrument (VI)

Compilation, Clumping

Clumps: Nodes that

can be executed together

LabVIEW VI• 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

• #Threads = #Cores * 4 Priority Levels * 5 Non-UI Execution Systems + 1 UI Execution System

Timing of a VI

• 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.

• Measured execution time contains VI execution as well as runtime system overhead

Achieving precise timing behavior with LabVIEW and NI hardware is possible …

… but it is not easy to get it right

Now: Future:

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 http://www.nist.gov/cps/cpspwg_timing.cfm

• Time-Aware Applications, Computers, and Communication Systems (TAACCS)http://www.taaccs.org/

• IEEE 802 standards group and the AVnu Alliance

• Industrial Internet Consortiumhttp://www.industrialinternetconsortium.org/

Date and Time Extensions to Ptolemy II

Patricia Derler

How does Ptolemy model time?

• Every director has a local clock that keeps track of model time/simulated time

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

ptolemy.data.type.BaseType.DateType

Actors to create and handle DateTokens

• Create DateTokens

• Modify DateTokens

• Convert DateTokens

• Relate model time to real time

Relate model time to real time

model time0 1 2 4 5

Relate model time to real time

model time0 1 2 4 5

10/16/2015 4:00pm 10/16/2015 4:05pmreal time

Relate model time to real time

model time0 1 2 4 5synchronizeToRealTime = true

output the model time value that

corresponds to the date

10/16/2015 4:00pm 10/16/2015 4:05pm

Relate model time to real time

model time0 1 2 4 5synchronizeToRealTime = true

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

Relate model time to real time

model time0 1 2 4 5synchronizeToRealTime = true

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

Thanks