IntroductionThis lesson introduces real-time concepts such as real time, determinism, and jitter. This lesson also discusses the components of a real-time system, including the host and the target. Use the Getting Started with the LabVIEW Real-Time Module manual to get started with the LabVIEW Real-Time Module quickly. To view the manual, select Help»Search the LabVIEW Help in LabVIEW to open the LabVIEW Help. Select the Contents tab, expand the Real-Time Module book in the table of contents, and open the Related Documentation topic. Click the Getting Started with the LabVIEW Real-Time Module link to open the document in your Web browser.
A. What is Real Time?The LabVIEW Real-Time Module combines LabVIEW graphical programming with the power of a real-time operating system, enabling you to build deterministic real-time applications. A misconception about real time is that it means quick. More accurately, real time means in-time. In other words, a real-time system ensures that responses occur in time, or on time. With general purpose operating systems, you cannot ensure that a response occurs within any given time period, and calculations might finish much later or earlier than you expect them to.For a system to be considered real time, all parts of it must be real time. For example, an application that runs in a real-time operating system may not behave with real-time characteristics. The application may rely on something that does not behave in real time, which causes the application to not behave in real time.Terms that frequently describe real-time systems are deterministic, loop cycle time, jitter, and embedded. Learning more about these terms helps you understand real time.
NoteThe puzzle symbol shown above indicates that you must complete this exercise for the course project. Look for this symbol on all course project exercises. Exercises are located at the end of each lesson.
Lesson 1 introduction to real time
Lesson 1 Introduction to Real TimeTOPICSA. What is Real-Time?B. RT HostC. RT Target ni.com/training
A. What is Real Time? Real Time Response: The ability to reliably and, without fail, respond to an event or perform an operation, within a guaranteed time period. ni.com/training
Real-Time TermsLoop Cycle Time • Execution time of one cycle of a loopJitter • Variation from the desired loop cycle timeDeterminism • Measure of jitter magnitudeLatency • Time required to respond to an event, or the time between input and output ni.com/training
Real-Time Terms (continued)Embedded • A computer system that is a component within a larger system. Embedded systems usually operate headlessly. ni.com/training
Maximum Jitter Jitter Range Desired Loop Time Maximum Jitter 1Loop Iteration 2 3 4 5 Loop Time (seconds) ni.com/training
Operating Systems • Processor time is shared between programs • Operating systems can preempt high priority VIs − Many programs run in the background—screen savers, disk utilities, virus software, and so on − It must service interrupts—keyboard, mouse, Ethernet, and so on • Cannot guarantee determinism—that is, it is a non-deterministic system ni.com/training
Real-Time Operating Systems• Ensure that high-priority tasks execute first• Do not require user input from peripheralsLabVIEW Real-Time Module executes VIs on the following:• Hardware targets running the Ardence Phar Lap Embedded Tool Suite (ETS)• Computers running Wind River VxWorks This course focuses on the ETS platform ni.com/training
Selecting an Operating SystemGeneral Real-Purpose Closed loop Data acquisition Time OS OS control Time-critical Offline analysis decisions Data presentation Extended run time Stand alone operation Increased reliability ni.com/training
LabVIEW Real-Time System Using ETS Host Computer RT Target Develop Execute Download ni.com/training
Discussion Exercise 1-1: Project Specification Document Read and discuss the Project Specification document and determine if real time is necessary for this application.GOAL ni.com/training
B. Real-Time Host Host Computer ni.com/training
C. Real-Time Targets Desktop PCs Determinism for PCI systems NI RT PXI Embedded Controllers High speed, high channel density, I/O variety NI RT Compact FieldPoint Small footprint, harsh environments LabVIEW Real-Time NI Compact Vision System Compact and distributed machine vision NI CompactRIO Reconfigurable Embedded System ni.com/training
Real-Time Hardware Configuration Desktop PCs Determinism for PCI systems NI RT PXI Embedded Controllers High speed, high channel density, I/O variety NI RT Compact FieldPointHost-Target Small footprint, harsh environments NI RT Compact Vision System Compact and distributed machine vision NI CompactRIO Reconfigurable Embedded System ni.com/training
RT Target – Host-Target ConfigurationNI RT Series PXI Controller—Ideal for high-speed, high channel count acquisitionNI cRIO Series—Embedded system with real-time controller, reconfigurable FPGA chassis, and industrial I/O modulesNI RT Series Compact FieldPoint Controller—Ideal for distributed real-time I/O applicationsNI 1450 Series Compact Vision System— Acquires, processes, and displays images for IEEE1394 camerasDesktop PCs as RT Targets—Ideal for low cost implementation ni.com/training
RT Target—cFP Controller Watchdog timer Removable CompactFlash memory (cFP-2x20 only) Onboard static memory Dedicated processor User-defined DIP switches and LEDs Serial port Backup power supply connection Ethernet port ni.com/training
Target Platform Comparison PXI cRIO cFP PC Loop Speed Best Better Good Best I/O Count High High High Low Rugged Better Best Best — Scalability Best Better Good Better Third-party RT HW Yes Yes No Yes Distributed Better Best Best Good ni.com/training
Summary – Matching Quiz1. Jitter A. How reliably a system responds to events or performs operations within a given time2. Determinism limit B. Time taken to execute one cycle of a loop3. Embedded C. Variation of loop cycle time from the4. Real time desired loop cycle time D. Computer system that is typically a5. Loop cycle component within a larger system time E. The ability to reliably, and without fail, respond to an event or perform an operation within a guaranteed time period ni.com/training