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1、Building Programmable Automation Controllers with LabVIEW FPGA1 OverviewProgrammable Automation Controllers 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 seamles
2、s 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 FPGA Mod
3、ule.With the LabVIEW FPGA Module and reconfigurable I/O 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 the family of
4、 RIO hardware targets without knowing low-level hardware description languages 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, digital, and counters
5、 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.2 Introduction You can use graphical programming in LabVIEW and t
6、he LabVIEW FPGA Module to configure the FPGA 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-design
7、ed hardware.An FPGA is a chip that consists of many unconfigured logic gates. Unlike the fixed, vendor-defined functionality of an ASIC chip, you can configure and reconfigure the logic on FPGAs for your specific application. FPGAs are used in applications where either the cost of developing and fab
8、ricating 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 decision making, and simu
9、ltaneous 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 not previously been made
10、 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 LabVIEW, a high-level graph
11、ical 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 process and generate synchroni
12、zed 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 3 NI RIO Hardware for PACs Historically, programming FPGAs has been li
13、mited 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 graphical development. M
14、easurement 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 between the LabVIEW FPGA
15、Module and the commercial off-the-shelf 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, and Compact Vision System platf
16、orms 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 provide analog and digital data
17、 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 discrete and analog control, custom
18、 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 CompactRIO to build an embedded sys
19、tem 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 C.NI Compact Vision System is
20、 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 CVS-145x systems use IEEE 13
21、94 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 application.4 Building PACs with LabVIE
22、W 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 it uses the same LabVIEW development en
23、vironment. 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 and functions, such as While Loops, For
24、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 digital I/O, and timing. You can use a combi
25、nation 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 communicates with the NI RIO hardware. This appl
26、ication reads from analog input 0 , performs the PID calculation, and outputs the resulting data on analog output 0 . 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 to execute. Analog control loops can run on an
27、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 PC processors, FPGAs are parallel processors. Add
28、ing 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. 5 FPGA Development Flow After you create the LabVIEW FPGA VI, you compile the code to run on the NI RIO hardware. Depe
29、nding 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 emulation mode so you can verify the logic of yo
30、ur 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 LabVIEW for Windows, such as execution highli
31、ghting, 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 host VI uses controls and indicators on the FPGA
32、 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 PC, PXI controller, Compact Vision System, or C
33、ompactRIO controller running a real-time operating system . 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 set of functions to develop a communication interfa
34、ce 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 reference, you read and write to the control and ind
35、icator 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 within a While Loop to continuously read and write
36、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 compiled FPGA VIs to the device to change or modify its fu
37、nctionality.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 on an RTOS with the LabVIEW Real-Time Module. LabVI
38、EW 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 performed in the LabVIEW Real-Time environment. Releva
39、nt 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 offers RIO hardware can run LabVIEW Real-Time VI.Figu
40、re 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 the device. In this configuration, as long as the FPGA
41、 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.6Using NI Soft Motion to Create Custom Motion Controllers The NI Soft Motion Development Module for LabVIEW provi
42、des 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 controller DSP. With it, you can handle path plan
43、ning, 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 Soft Motion includes functions for trajectory generator and spline engine and examples with complete source code fo
44、r 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 either on a LabVIEW Real-Time target at millisecond
45、 loop rates or on a LabVIEW FPGA target at microsecond loop rates.7 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 applications requiring custom hardware. These custom appl
46、ications 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:7.1 Batch control7.2 Discrete control7.3 Motion control7.4 In-vehicle data acquisition7.5 Machine con
47、dition monitoring7.6 Rapid control prototyping 7.7 Industrial control and acquisition7.8 Distributed data acquisition and control7.9 Mobile/portable noise, vibration, and harshness analysis 8 Conclusion The LabVIEW FPGA Module brings the flexibility, performance, and customization of FPGAs to PAC pl
48、atforms. 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
49、 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 and NI RIO hardware as part of your NI PAC adds significant flexibility and functionality for applications requiring ultrahigh-speed control, interfaces to custom digital protocols, or a custom I/O mix of analog, digita
