LabVIEW编程思想探索

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"LabVIEW Style Book（EN）是一本针对LabVIEW高级用户的书籍，主要探讨了如何构建更高效、更具可读性和可维护性的程序结构。作者和出版社在书中尽可能地考虑了各种设计模式和最佳实践，旨在帮助读者提升LabVIEW编程技能。尽管书中可能涉及制造商和销售商的产品标识，但其主要焦点是编程技巧和结构思维，而不是产品推广。需要注意的是，书中提供的信息可能存在误差或遗漏，作者和出版社对此不承担任何直接或间接的责任。对于大量购买或特殊销售需求，如电子版本、定制封面或特定于业务、培训目标、市场定位和品牌兴趣的内容，出版社提供优惠折扣政策。" 此书的内容可能涵盖以下LabVIEW相关的知识点： 1. **程序结构**：书中会深入讲解如何组织和设计LabVIEW程序，包括数据流管理、模块化编程、错误处理策略、并行处理和多线程等。 2. **最佳实践**：介绍LabVIEW编程中的最佳实践，例如如何编写清晰的VI布局、使用适当的数据类型和控件，以及如何有效地利用LabVIEW的内置函数和工具。 3. **代码重用**：探讨如何创建和使用库来实现代码重用，提高开发效率和代码质量。 4. **文档和注释**：强调在LabVIEW程序中添加注释和文档的重要性，以提高代码的可读性和团队协作能力。 5. **测试和调试**：讨论如何构建有效的测试框架，使用调试工具来定位和修复程序中的问题。 6. **性能优化**：讲解如何优化代码以获得更好的运行效率，包括内存管理、计算性能和用户界面响应速度。 7. **错误处理**：介绍LabVIEW的错误处理机制，如使用错误线和错误结构，以及如何优雅地处理程序异常。 8. **高级特性**：可能会涉及LabVIEW的高级特性，如G子VI、自定义函数节点、动态数据和实时系统应用。 9. **VI设计原则**：书中可能会阐述一些关于VI设计的基本原则，如遵循DRY（Don't Repeat Yourself）和KISS（Keep It Simple, Stupid）原则。 10. **案例研究**：通过实际案例分析，展示如何将理论知识应用于解决实际工程问题。通过阅读这本书，LabVIEW开发者可以学习到如何编写更加专业和高效的程序，提升自己的编程水平，同时也能更好地适应团队合作和项目管理的需求。无论你是初学者还是有经验的开发者，这本书都可能为你提供有价值的洞见和建议。

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Meticulous VI in Figure 1-1 is a highly complex application used in the medical industry for patient physiologic data

monitoring. It has a very professional and highly organized appearance. The front panel is densely functional yet appears

neat and intuitive. The diagram is impressive, containing multiple parallel loops, networks of labeled wires, advanced

constructs, and liberal documentation. Nested VI in Figure 1-2 is a relatively simple application that controls a

scientific instrument. It has a clean, uncluttered front panel and block diagram. The most noteworthy characteristic

is the diagram's multiple layers of structures nested within structures. Spaghetti VI in Figure 1-3 is an automated

test application with medium complexity. The front panel contains many different colors and font styles, which tend

to clash and distract the user. The diagram is a labyrinth of wires and nodes compacted together within a single loop.

So dissimilar are these three programming styles that it is worth noting that all three examples are commercial

applications developed by experienced LabVIEW professionals. Style is the main differentiator.

Let us break down Theorem 1.1 into seven different parts and evaluate each one individually: ease of use, efficiency,

readability, maintainability, robustness, simplicity, and performance. Several of these terms are general, subjective,

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ambiguous, and overlapping. Therefore, each section begins with a definition of how the term is used here and then discusses

how that term relates to development style.

Ease of use is the ease with which the end user operates the software and accomplishes her objectives. This involves

interacting with the application's graphical user interface (GUI). Ease of use ranges in importance from less important,

for a one-time experiment to be run only by the application's developer, who is intimately familiar with the software;

to very important, for a production application to be used by a variety of semiskilled operators within a single

organization; to extremely important, for a mission- or safety-critical application, or a commercial application intended

for distribution and resale. If you are designing a commercial application, read a GUI style reference for your

application's target operating system. If your application is mission or safety critical, read an appropriate text on

human factors. The LabVIEW Style Book contains general style rules that can be applied to most LabVIEW applications,

from the lab to production, on most operating systems, from desktop PCs running Windows to embedded processors running

a real-time or hand-held operating system.

Ease of use is related to readability and responsiveness of the GUI. In Figure 1-1, the front panel for Meticulous VI

is intuitively laid out. The principal physiologic data is displayed in stacked waveform charts and large numeric

indicators in the center of the panel. Ancillary data is contained on separate display screens. Boolean controls facilitate

navigation in a conventional manner. The overall appearance resembles and behaves as a virtual instrument. The application

is fast and responds quickly to operations that the user performs.

The front panel of Nested VI in Figure 1-2 uses a tab control to logically organize the front panel objects. The controls

are clearly labeled and evenly spaced. However, the purpose of each tab and the order by which the user navigates the

GUI are not immediately clear. The diagram contains Sequence structures that execute each frame to completion, regardless

of any operations the user performs on the front panel. Its capability to respond to the user clicking Quit depends

upon which frame of the Sequence structure the application is executing when the button's value changes.

The front panel of Spaghetti VI, shown in Figure 1-3, organizes controls and indicators using clusters. It is logical

and organized, but it contains too many colors and font types, and not enough empty areas or "white space." More important,

the performance is not reliable. No matter how attractive a GUI appears, if it does not perform its intended function,

it will not provide a positive user experience.

Chapter 3, "Front Panel Style," contains style rules for front panel design that promote consistency and ease of use

for your GUIs. Chapter 6, "Data Structures," and Chapter 8, "Design Patterns," provide additional style rules that help

optimize the responsiveness of the GUI.

Efficiency pertains to the use of processor, memory, and input/output (I/O) resources. An efficient LabVIEW application

executes quickly, without performing unnecessary operations, particularly ones that are performed repeatedly within

looping structures. An efficient application also conserves memory by limiting the size of the four LabVIEW memory

components: the front panel, block diagram, data space, and code. Front panel and block diagram memory store the graphical

objects and images that comprise the front panel and block diagram, respectively. Data space memory contains all the

data that flows through the diagram, as well as the diagram constants, default values for front panel controls, and

the data that is copied when written to variables and front panel indicators. Code is the portion of memory that contains

the compiled source code. Finally, efficient applications minimize I/O operations, such as GUI updates, instrument and

network communications, and data acquisition (DAQ) calls. Execution speed and memory use are related. Memory and disk

operations are a principal source of latencies in all modern computing devices. As memory consumption grows during the

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execution of an application, LabVIEW's memory manager is called upon to allocate new and larger memory blocks. This

causes a delay while the memory manager runs and results in fragmented memory, for which some of the previous blocks

are not efficiently used. The memory manager is a wonderful aspect of LabVIEW that handles memory allocation automatically.

However, developers should be aware of the types of operations that might cause it to run and avoid these situations

from occurring unnecessarily.

LabVIEW contains a tool called the Profile Performance and Memory window that directly measures the execution speed

and data memory of all VIs loaded in memory. This tool, shown in Figure 1-4, is accessed by selecting

Tools»Profile»Performance and Memory. This is an excellent tool for helping to improve the efficiency of an application.

Use the Profile Performance and Memory window to determine which VIs consume the most time and memory, and examine those

more closely. You can optimize your VI's efficiency by iteratively making improvements and checking the profile metrics.

Figure 1-4. The LabVIEW Profile Performance and Memory window displays the data memory of Meticulous VI.

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Note that the efficiency of distinctly different applications, such as Meticulous VI, Nested VI, and Spaghetti VI, cannot

be compared in any meaningful way. This is because execution time, memory consumption, and I/O depend on the application's

requirements as well as the developer's programming style. For example, metrics from the Profile Performance and Memory

window might indicate that Nested VI executes the fastest and uses the least memory. However, Nested VI is the least

resource-demanding of the three applications and might even have plenty of room for further optimization. The Profile

Performance and Memory window is best used for measuring the change in efficiency of a single application when incremental

modifications have been made.

An alternate method of evaluating efficiency is simply to inspect the application for sources of inefficiency. Look

for unnecessary operations within loops and for operations that create new data buffers. The diagram of Spaghetti VI

(see Figure 1-3), for example, contains many nodes within the main While Loop. This includes read local variables, which

make copies of their data when read from, and Property Nodes that are written within every iteration, regardless of

whether their value has changed.

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Inspecting the diagram of Nested VI (see Figure 1-2) reveals a tight loop, in which several control terminals are polled

within the innermost While Loop as fast as the loop can run. High-speed GUI polling is not an efficient use of the processor.

Most humans cannot distinguish between a 1 millisecond (ms) and a 100ms GUI response. More efficient alternatives include

adding a delay using the Wait (ms) function or using an Event structure to service all user interface activity. These

alternatives free the processor to work on parallel tasks and applications.

Meticulous VI (see Figure 1-1) uses multiple parallel loops on one diagram, many shift registers, and an Event structure.

The following tasks execute in their own separate parallel loop: GUI event handling, instrument communications, data

parsing, data logging, data review, data display, and error handling. A total of eight parallel loops are used. Each

loop is finely tuned for optimum performance. However, the top-level diagram is extremely large, resulting in very large

data and diagram memory components. The four components of memory use are provided in the VI Properties window, shown

in Figure 1-5. You access the VI Properties window by selecting File»VI Properties and then selecting Memory Usage for

the category.

Figure 1-5. The VI Properties window indicates the four categories of memory use for Meticulous VI.

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Event structures are the most efficient method of capturing user interface activity. The GUI event handling loop sleeps,

using no processor time, until it receives a registered event from the operating system. This is both more efficient

and much more responsive than polling the control terminals in a loop. Hence, Meticulous VI is maximally responsive

to GUI events. Finally, Meticulous VI makes extensive use of shift registers for passing data between loop iterations,

and queues for passing data between parallel loops. Shift registers are much more efficient alternatives to variables,

and queues are much more functional.

Nested VI makes good use of subVIs, which increase memory efficiency, but uses Sequence structures, which can decrease

processing efficiency. SubVIs reduce the quantity of nodes on the diagram, which reduces block diagram memory. In addition,

LabVIEW can reclaim memory buffers used by subVIs when the subVIs are not executing, thereby reducing data memory use.

However, the nested structures, particularly the Sequence structures, are a potential source of inefficiency. When a

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Sequence structure is called, all frames must execute through completion, in consecutive order. In many situations,

it is preferable to reorder or abort the sequence, to improve its efficiency.

The style rules presented throughout this book promote maximum efficiency. Chapter 4, "Block Diagram," and Chapter 8,

"Design Patterns," discuss rules that influence processing efficiency. Chapter 6, "Data Structures," presents rules

for efficient memory use.

Readability refers to how easily the developer can comprehend the source code. This includes both the front panel and

the block diagram. The objects on the front panel should be clearly labeled and easily identified. The diagram should

be neat, orderly, and easy to follow. The application should be well documented throughout.

The front panel of Meticulous VI appears both simple and perhaps a little mysterious. Figure 1-6 shows the front panel

in edit mode. The menu controls along the bottom and right perimeters are Boolean controls with customized appearance

and embedded text. A knob is used for rapid menu and waveform navigation. The main display area resembles a collage

of indicators suspended on a black background. It is divided into two sections, a large subpanel control on the left

and multiple overlapping indicators on the right. Twelve preset display configurations can be programmed by dynamically

loading any one of twelve subVIs into the subpanel and making a subset of the overlapping indicators visible. The indicators

are customized with a transparent background overlaid on a black decoration, giving them the appearance of floating

in space. The diagram (see Figure 1-1) is easy to follow because all data flows through wires from left to right, with

no more than one bend to wrap around structures and objects. The diagram is extensively documented, including visible

terminal labels, free labels on long wires and within each structure, and enumerated case selectors.

Figure 1-6. The front panel of Meticulous VI in edit mode. It contains customized Boolean controls along the bottom

and right perimeters, a knob, a subpanel control, and multiple overlapping indicators.

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