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1、A 英文原文 Building Programmable Automation Controllers with LabVIEW FPGAOverviewProgrammable Automation Controllers (PACs) are gaining acceptance within the industrial control market as the ideal solution for applications that require highly integrated analog and digital I/O, floating-point processing,
2、 and seamless connectivity to multiple processing nodes. National Instruments offers a variety of PAC solutions powered by one common software development environment, NI LabVIEW. With LabVIEW, you can build custom I/O interfaces for industrial applications using add-on software, such as the NI LabV
3、IEW FPGA Module. With the LabVIEW FPGA Module and reconfigurable I/O (RIO) hardware, National Instruments delivers an intuitive, accessible solution for incorporating the flexibility and customizability of FPGA technology into industrial PAC systems. You can define the logic embedded in FPGA chips a
4、cross the family of RIO hardware targets without knowing low-level hardware description languages (HDLs) or board-level hardware design details, as well as quickly define hardware for ultrahigh-speed control, customized timing and synchronization, low-level signal processing, and custom I/O with ana
5、log, digital, and counters within a single device. You also can integrate your custom NI RIO hardware with image acquisition and analysis, motion control, and industrial protocols, such as CAN and RS232, to rapidly prototype and implement a complete PAC system.Table of Contents1. Introduction 2. NI
6、RIO Hardware for PACs 3. Building PACs with LabVIEW and the LabVIEW FPGA Module 4. FPGA Development Flow 5. Using NI SoftMotion to Create Custom Motion Controllers 6. Applications 7. Conclusion Introduction You can use graphical programming in LabVIEW and the LabVIEW FPGA Module to configure the FPG
7、A (field-programmable gate array) on NI RIO devices. RIO technology, the merging of LabVIEW graphical programming with FPGAs on NI RIO hardware, provides a flexible platform for creating sophisticated measurement and control systems that you could previously create only with custom-designed hardware
8、.An FPGA is a chip that consists of many unconfigured logic gates. Unlike the fixed, vendor-defined functionality of an ASIC (application-specific integrated circuit) chip, you can configure and reconfigure the logic on FPGAs for your specific application. FPGAs are used in applications where either
9、 the cost of developing and fabricating an ASIC is prohibitive, or the hardware must be reconfigured after being placed into service. The flexible, software-programmable architecture of FPGAs offer benefits such as high-performance execution of custom algorithms, precise timing and synchronization,
10、rapid decision making, and simultaneous execution of parallel tasks. Today, FPGAs appear in such devices as instruments, consumer electronics, automobiles, aircraft, copy machines, and application-specific computer hardware. While FPGAs are often used in industrial control products, FPGA functionali
11、ty has not previously been made accessible to industrial control engineers. Defining FPGAs has historically required expertise using HDL programming or complex design tools used more by hardware design engineers than by control engineers.With the LabVIEW FPGA Module and NI RIO hardware, you now can
12、use LabVIEW, a high-level graphical development environment designed specifically for measurement and control applications, to create PACs that have the customization, flexibility, and high-performance of FPGAs. Because the LabVIEW FPGA Module configures custom circuitry in hardware, your system can
13、 process and generate synchronized analog and digital signals rapidly and deterministically. Figure A1 illustrates many of the NI RIO devices that you can configure using the LabVIEW FPGA Module.Figure A1 LabVIEW FPGA VI Block Diagram and RIO Hardware Platforms NI RIO Hardware for PACs Historically,
14、 programming FPGAs has been limited to engineers who have in-depth knowledge of VHDL or other low-level design tools, which require overcoming a very steep learning curve. With the LabVIEW FPGA Module, NI has opened FPGA technology to a broader set of engineers who can now define FPGA logic using La
15、bVIEW graphical development. Measurement and control engineers can focus primarily on their test and control application, where their expertise lies, rather than the low-level semantics of transferring logic into the cells of the chip. The LabVIEW FPGA Module model works because of the tight integra
16、tion between the LabVIEW FPGA Module and the commercial off-the-shelf (COTS) hardware architecture of the FPGA and surrounding I/O components.National Instruments PACs provide modular, off-the-shelf platforms for your industrial control applications. With the implementation of RIO technology on PCI,
17、 PXI, and Compact Vision System platforms and the introduction of RIO-based CompactRIO, engineers now have the benefits of a COTS platform with the high-performance, flexibility, and customization benefits of FPGAs at their disposal to build PACs. National Instruments PCI and PXI R Series plug-in de
18、vices provide analog and digital data acquisition and control for high-performance, user-configurable timing and synchronization, as well as onboard decision making on a single device. Using these off-the-shelf devices, you can extend your NI PXI or PCI industrial control system to include high-spee
19、d discrete and analog control, custom sensor interfaces, and precise timing and control. NI CompactRIO, a platform centered on RIO technology, provides a small, industrially rugged, modular PAC platform that gives you high-performance I/O and unprecedented flexibility in system timing. You can use N
20、I CompactRIO to build an embedded system for applications such as in-vehicle data acquisition, mobile NVH testing, and embedded machine control systems. The rugged NI CompactRIO system is industrially rated and certified, and it is designed for greater than 50 g of shock at a temperature range of -4
21、0 to 70 C.NI Compact Vision System is a rugged machine vision package that withstands the harsh environments common in robotics, automated test, and industrial inspection systems. NI CVS-145x devices offer unprecedented I/O capabilities and network connectivity for distributed machine vision applica
22、tions.NI CVS-145x systems use IEEE 1394 (FireWire) technology, compatible with more than 40 cameras with a wide range of functionality, performance, and price. NI CVS-1455 and NI CVS-1456 devices contain configurable FPGAs so you can implement custom counters, timing, or motor control in your machin
23、e vision application.Building PACs with LabVIEW and the LabVIEW FPGA ModuleWith LabVIEW and the LabVIEW FPGA Module, you add significant flexibility and customization to your industrial control hardware. Because many PACs are already programmed using LabVIEW, programming FPGAs with LabVIEW is easy b
24、ecause it uses the same LabVIEW development environment. When you target the FPGA on an NI RIO device, LabVIEW displays only the functions that can be implemented in the FPGA, further easing the use of LabVIEW to program FPGAs. The LabVIEW FPGA Module Functions palette includes typical LabVIEW struc
25、tures and functions, such as While Loops, For Loops, Case Structures, and Sequence Structures as well as a dedicated set of LabVIEW FPGA-specific functions for math, signal generation and analysis, linear and nonlinear control, comparison logic, array and cluster manipulation, occurrences, analog an
26、d digital I/O, and timing. You can use a combination of these functions to define logic and embed intelligence onto your NI RIO device.Figure A2 shows an FPGA application that implements a PID control algorithm on the NI RIO hardware and a host application on a Windows machine or an RT target that c
27、ommunicates with the NI RIO hardware. This application reads from analog input 0 (AI0), performs the PID calculation, and outputs the resulting data on analog output 0 (AO0). While the FPGA clock runs at 40 MHz the loop in this example runs much slower because each component takes longer than one-cl
28、ock cycle to execute. Analog control loops can run on an FPGA at a rate of about 200 kHz. You can specify the clock rate at compile time. This example shows only one PID loop; however, creating additional functionality on the NI RIO device is merely a matter of adding another While Loop. Unlike trad
29、itional PC processors, FPGAs are parallel processors. Adding additional loops to your application does not affect the performance of your PID loop.FPGA Development Flow After you create the LabVIEW FPGA VI, you compile the code to run on the NI RIO hardware. Depending on the complexity of your code
30、and the specifications of your development system, compile time for an FPGA VI can range from minutes to several hours. To maximize development productivity, with the R Series RIO devices you can use a bit-accurate emulation mode so you can verify the logic of your design before initiating the compi
31、le process. When you target the FPGA Device Emulator, LabVIEW accesses I/O from the device and executes the VI logic on the Windows development computer. In this mode, you can use the same debugging tools available in LabVIEW for Windows, such as execution highlighting, probes, and breakpoints.Once
32、the LabVIEW FPGA code is compiled, you create a LabVIEW host VI to integrate your NI RIO hardware into the rest of your PAC system. Figure A3 illustrates the development process for creating an FPGA application. The host VI uses controls and indicators on the FPGA VI front panel to transfer data bet
33、ween the FPGA on the RIO device and the host processing engine. These front panel objects are represented as data registers within the FPGA. The host computer can be either a PC or PXI controller running Windows or a PC, PXI controller, Compact Vision System, or CompactRIO controller running a real-
34、time operating system (RTOS). In the above example, we exchange the set point, PID gains, loop rate, AI0, and AO0 data with the LabVIEW host VI.The NI RIO device driver includes a set of functions to develop a communication interface to the FPGA. The first step in building a host VI is to open a ref
35、erence to the FPGA VI and RIO device. The Open FPGA VI Reference function, as seen in Figure A2, also downloads and runs the compiled FPGA code during execution. After opening the reference, you read and write to the control and indicator registers on the FPGA using the Read/Write Control function.
36、Once you wire the FPGA reference into this function, you can simply selectFigure A2 PID Control Using an Embedded LabVIEW FPGA VI with Corresponding LabVIEW Host VI. Figure A3 LabVIEW FPGA Development Flowwhich controls and indicators you want to read and write to. You can enclose the FPGA Read/Writ
37、e function within a While Loop to continuously read and write to the FPGA. Finally, the last function within the LabVIEW host VI in Figure A2 is the Close FPGA VI Reference function. The Close FPGA VI Reference function stops the FPGA VI and closes the reference to the device. Now you can download o
38、ther compiled FPGA VIs to the device to change or modify its functionality.The LabVIEW host VI can also be used to perform floating-point calculations, data logging, networking, and any calculations that do not fit within the FPGA fabric. For added determinism and reliability, you can run your host
39、application on an RTOS with the LabVIEW Real-Time Module. LabVIEW Real-Time systems provide deterministic processing engines for functions performed synchronously or asynchronously to the FPGA. For example, floating-point arithmetic, including FFTs, PID calculations, and custom control algorithms, a
40、re often performed in the LabVIEW Real-Time environment. Relevant data can be stored on a LabVIEW Real-Time system or transferred to a Windows host computer for off-line analysis, data logging, or user interface displays. The architecture for this configuration is shown in Figure A4. Each NI PAC pla
41、tform that offers RIO hardware can run LabVIEW Real-Time VIs.Figure A4 Complete PAC Architecture Using LabVIEW FPGA, LabVIEW Real-Time and Host PCWithin each R Series and CompactRIO device, there is flash memory available to store a compiled LabVIEW FPGA VI and run the application immediately upon p
42、ower up of the device. In this configuration, as long as the FPGA has power, it runs the FPGA VI, even if the host computer crashes or is powered down. This is ideal for programming safety power down and power up sequences when unexpected events occur.Using NI SoftMotion to Create Custom Motion Cont
43、rollers The NI SoftMotion Development Module for LabVIEW provides VIs and functions to help you build custom motion controllers as part of NI PAC hardware platforms that can include NI RIO devices, DAQ devices, and Compact FieldPoint. NI SoftMotion provides all of the functions that typically reside
44、 on a motion controller DSP. With it, you can handle path planning, trajectory generation, and position and velocity loop control in the NI LabVIEW environment and then deploy the code on LabVIEW Real-Time or LabVIEW FPGA-based target hardware.NI SoftMotion includes functions for trajectory generato
45、r and spline engine and examples with complete source code for supervisory control, position, and velocity control loop using the PID algorithm. Supervisory control and the trajectory generator run on a LabVIEW Real-Time target and run at millisecond loop rates. The spline engine and the control loo
46、p can run either on a LabVIEW Real-Time target at millisecond loop rates or on a LabVIEW FPGA target at microsecond loop rates.Applications Because the LabVIEW FPGA Module can configure low-level hardware design of FPGAs and use the FPGAs within in a modular system, it is ideal for industrial contro
47、l applications requiring custom hardware. These custom applications can include a custom mix of analog, digital, and counter/timer I/O, analog control up to 125 kHz, digital control up to 20 MHz, and interfacing to custom digital protocols for the following: Batch control Discrete control Motion con
48、trol In-vehicle data acquisition Machine condition monitoring Rapid control prototyping (RCP) Industrial control and acquisition Distributed data acquisition and control Mobile/portable noise, vibration, and harshness (NVH) analysisConclusion The LabVIEW FPGA Module brings the flexibility, performan
49、ce, and customization of FPGAs to PAC platforms. Using NI RIO devices and LabVIEW graphical programming, you can build flexible and custom hardware using the COTS hardware often required in industrial control applications. Because you are using LabVIEW, a programming language already used in many industrial control applications, to define your NI RIO hardware, there is no need to learn VHDL or other low-level hardware design tools to create custom hardware. Using the