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1、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, and se
2、amless 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 LabVIEW FPG
3、A 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 across t
4、he 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 analog, di
5、gital, 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 RIO Har
6、dware 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 FPGA (fiel
7、d-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.An FPG
8、A 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 the co
9、st 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, rapid d
10、ecision 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 functionality has
11、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 use Lab
12、VIEW, 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 proces
13、s and generate synchronized analog and digital signals rapidly and deterministically. Figure 1 illustrates many of the NI RIO devices that you can configure using the LabVIEW FPGA Module.Figure 1. LabVIEW FPGA VI Block Diagram and RIO Hardware Platforms NI RIO Hardware for PACs Historically, program
14、ming 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 LabVIEW gr
15、aphical 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 integration bet
16、ween 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, PXI, an
17、d 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 devices pr
18、ovide 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-speed discre
19、te 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 NI Compac
20、tRIO 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 -40 to 70
21、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 applications.NI
22、 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 machine vision
23、 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 because i
24、t 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 structures an
25、d 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 and digita
26、l I/O, and timing. You can use a combination of these functions to define logic and embed intelligence onto your NI RIO device.Figure 2 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 communicat
27、es 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-clock cycle
28、 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 traditional P
29、C processors, FPGAs are parallel processors. Adding additional loops to your application does not affect the performance of your PID loop.Figure 2. PID Control Using an Embedded LabVIEW FPGA VI with Corresponding LabVIEW Host VI. FPGA Development Flow After you create the LabVIEW FPGA VI, you compil
30、e the code to run on the NI RIO hardware. Depending on the complexity of your code 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 em
31、ulation mode so you can verify the logic of your design before initiating the compile 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
32、 LabVIEW for Windows, such as execution highlighting, probes, and breakpoints.Once 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 3 illustrates the development process for creating an FPGA application. The ho
33、st VI uses controls and indicators on the FPGA VI front panel to transfer data between 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 P
34、C, PXI controller, Compact Vision System, or CompactRIO controller running a real-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.Figure 3. LabVIEW FPGA Development FlowThe NI RIO device driver includes a
35、 set of functions to develop a communication interface to the FPGA. The first step in building a host VI is to open a reference to the FPGA VI and RIO device. The Open FPGA VI Reference function, as seen in Figure 2, also downloads and runs the compiled FPGA code during execution. After opening the
36、reference, you read and write to the control and indicator registers on the FPGA using the Read/Write Control function. Once you wire the FPGA reference into this function, you can simply select which controls and indicators you want to read and write to. You can enclose the FPGA Read/Write function
37、 within a While Loop to continuously read and write to the FPGA. Finally, the last function within the LabVIEW host VI in Figure 2 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 other compil
38、ed 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 application
39、 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, are often pe
40、rformed 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 4. Each NI PAC platform that o
41、ffers RIO hardware can run LabVIEW Real-Time VIs.Figure 4. 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 power up of t
42、he 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 Controllers The
43、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 on a motion
44、 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 generator and spline
45、 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 loop can run ei
46、ther 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 control applicatio
47、ns 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 control In-vehi
48、cle 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, performance, and cust
49、omization 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 LabVIEW FPGA Module a