LabVIEW State Machine Architectures

LabVIEW State Machine Architectures. Presented By Scott Sirrine Eaton Corporation. State Machines- Personal Background. Employment Lead Product Engineer (Software development) at Eaton Corporation’s R&D facility in Galesburg MI. LabVIEW developer for 12 years (version 3.1)
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LabVIEW State Machine ArchitecturesPresented By Scott Sirrine Eaton CorporationState Machines- Personal Background
  • Employment
  • Lead Product Engineer (Software development) at Eaton Corporation’s R&D facility in Galesburg MI.
  • LabVIEW developer for 12 years (version 3.1)
  • Data Acquisition and Control
  • NVH
  • Vehicle bus applications (Can/J1939)
  • Certifications
  • Certified LabVIEW Architect since Aug 2003
  • Certified LabVIEW Developer Oct 2002
  • Education
  • Master (MSCIS)
  • Bachelor (BSCIS)
  • Associate electronics
  • State Machines- Overview
  • Discuss the concept of “State Machines” as they pertain to LabVIEW based application development. Focus will be on design considerations and merits for selecting various State Machines models.
  • Topics
  • Single loop
  • Multiple Loops (Asynchronous)
  • Supporting techniques
  • Queue
  • Functional Globals
  • Multi-threading and performance (comments)
  • State Machines- Definition
  • Wikipedia- Model of behavior composed of finite number of states, transitions between those states, and actions. Made up of entry, exit, input, and transition actions. Used quite a bit in UML based modeling (decision trees/flowcharts).
  • LabVIEW Based State Machine- Decision based execution framework. Based on a While loop used in conjunction with a Case statement and a shift register. Branch control can be enhanced by the use of Events, queues, and functional globals.
  • Note: Due to LabVIEW’s inherent parallelism, execution performance can be further enhanced by the use of multiple state machines running in parallel.State Machines- Single Loop
  • This is an example of a basic state machine with a while loop, case statement, and shift register. It has been enhanced slightly to include a event structure for capturing user actions.
  • Uses
  • Main Application VI
  • Intermediate VI
  • VIs with complex execution and decision trees
  • Pros
  • Easy to implement
  • Very Scalable
  • Error handling
  • Input validation
  • Cons
  • Additional overhead vs. pass-though
  • No history
  • Single exit branch (without adding extra code)
  • State Machines- Multiple Loops
  • Multiple execution loops better leverage LabVIEW’s inherent parallelism.
  • Separate loop for User IO allows the main application to continue acquiring data if program focus passes to a popup window.
  • Uses
  • Primarily the main application VI
  • Pros
  • Parallelism
  • Leverages Multi-core CPU
  • Asynchronous (potential)
  • Cons
  • More complex loop interaction
  • More complex data buffering
  • State Machines- Multiple Loops cont.
  • Loop 1- Acquisition, Scaling, and Display updates.
  • Loop 2- Test Control
  • Loop 3- User Interface
  • This is an example of data acquisition, analysis, and control application running 3 asynchronous loops. The application offers better determinism, CPU utilization, and scales well with multiple CPU cores.
  • State Machines- Multiple Loops cont.
  • This is an example of vehicle bus acquisition running 3 asynchronous loops. Display updates are performed in a separate loop from the data acquisition. This allows the daq loop to sample data at a faster rate than the real-time display updates.
  • Loop 1- Acquisition, Scaling, and data logging.
  • Loop 2- Display updates
  • Loop 3- User Interface
  • Loop 3Loop 1Loop 2State Machines- QueuesShutdown steps if not logging data.
  • Queues are located under the “Synchronization” palette and function as a stack (FIFO). A queue can enhance the function of a state machine’s shift register by queuing up multiple actions.
  • In this example assume the VI was acquiringdata and a hardware error occurred. Depending on if the VI was logging data or simply to update displays will determine the states needed for proper shutdown. Without a queue, special states for each of these event would need to be developed, which adds to the VI’s overall size and complexity.Shutdown steps if actively logging data.Pros
  • Easy to implement
  • Very Scalable
  • Simpler states
  • Multiple exit states
  • Cons
  • Small amount of extra code
  • State Machines- Functional Globals
  • A functional global is simply a VI with a while loop and a case statement with a un-initialized shift register. Because the shit register is un-initialized it retains state as long as the VI is loaded in memory.
  • These globals do not make multiple memory copies like a “global” variable and can make a very tangible impact on overall memory footprint.
  • If the functional global’s execution is not set to “Reentrant” there is only one instance in memory and race conditions are avoided.
  • In the context of the state machine, it can be used to exchange data between the loops.
  • Note: The biggest negative is overuse of FGs goes against the concept of dataflow.State Machines- The Global Queue
  • In the earlier Daq/Analysis/Control application each loop uses a queue. To better support inter-loop control, the queues themselves were placed in a functional global. This simplified interaction with the various queues.
  • State Machines- Conclusion
  • This presentation is by no means a comprehensive discussion of the concept of state machine, but instead tries to highlight the opportunities offered by LabVIEW to develop powerful application which are not only multi-threaded, but harness multi-core. LabVIEW has served me well in developing stable and fast applications over the years, and hopefully it is proving just as useful to all of you.
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