LabVIEW Queued State Machine Architecture.pdfLabVI

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详细说明：LabVIEW Queued State Machine Architecture 详细使用方法讲解，高清，每一页都十分清晰！articles in the now discontinued publication: LabVIEW Technical resource Guide". the subject was introduced by Jeff Parker (Winter, 1995)and elaborated and modified by Greg Fowler(Spring, 1996)and Lance Butler(Winter, 1996).The National instruments website hosts various knowledge-base articles and tutorials matching the key word: "Queued State Machine. National Instruments Kevin Hogan produced a useful presentation and web cast on this same subject matter that continues to be available as of this writing. NI LabVIEW courses from labview basics ii to the advanced course all cover material on queued state machine architecture. over the years the queued state machine has gained advocacy and widespread use in large LabVIEW-based applications in the developer community. In light of this situation, an NI forum thread: 'Please Don' t Do It emerged in June 2006 that engages a lively discussion that questions QSM-PC architecture suitability in certain lab vieW coding scenarios Queued State Machine Producer Consumer Design Objects Generally, a queued state machine is a LabVIEW programming method that sends commands and other data from multiple source points (i.e. producer points), such as from user events and 3/32 from one or more parallel processes, and gets these handled in one state machine process (i.e. destination consumer point)in the order in which they were added to the queue. Figure 1 is the simplest high-level illustration of the QSM-PC design. Figure 2 adds detail to this illustration, and Figure 3 is the equivalent LabVIEW implementation these illustrations will be used through-out this article to clarify the features and functions of the QSM-PC architecture Blocklayout of Queued State Machine E/ET LOOP [/ 3 CUMMANISHANDLEROrPRUCESSIR f Consumer/ S SuoYI PIICESS T PROCESS2 PROGESSN (/ Figure 1 Shows four high-level objects of queued state machine producer consumer architecture. I=Queue reference;' 2=User events object (producer of commands and data) 3=Commands processor(consumer process that handles commands and data) 4= Parallel SubvI processes (producer of commands and data) 4/32 ANBTORTy80 ed state Macti加B EvN区 STATEN QuEuE 15 An PARALLEL PARALLEL PARALLEL PROCESS PROCESS PROCESS Figure 2. Queued state machine producer consumer architecture showing data flow and objects inside the consumer process. 鲁一 State Machine ET▲ 12 a于 1.3 5/32 Figure 3. Lab vIEW implementation of the queued state machine producerconsumer architecture. Labeled objects I through 4 match those of the high eve/illustrations in Figure 1 and Fiqure 2. A High Level Layout of QSM-PC Architecture a general layout of QSM-PC architecture comprises of the four objects annotated by the encircled numerals 1 to 4 shown in Figure 1. These objects are namely: (1)Queue reference object;(2)User events object(optional for head-less embedded applications that require no user interaction);(3)Main state machine object; (4)One or more parallel processes subVI objects Note that label 1.1 in Figure 1, is a broken-line representation of the queue reference object. The broken -line is meant to show that the subvi processes are able to access and interact with the queue from within the Subvi by referencing the queue by name without having to wire the queue reference to the SubVis. see the lab vieW implementation of this illustration in Figure 3 and the QsM-PC LabVIEW Example included in this article Queue reterence access by name also allows a queue reterence to be use by dynamically launched Vis by Vi Server and is discussed further under the section: Item (1) Queue Reterence Object. 6/32 Items(2)and (4 )are the multiple producer processes responsible for sourcing commands and data and adding them to the queue Item(3)is the single consumer process which removes commands and data from the queue name: Main Queue and acts on these in the order added to the queue. One important rule is that, for any one queue reference you should only have one consumer process while there can be one or more producer processes. This rule ensures that the consumer process is the central command processing center where each and every command added to the queue reference gets handled In the abVIEW QSM-PC layout of Figure 3 the consumer process is part of the open top level block diagram, rather than a subVi This is to facilitate manipulation of controls, indicators and properties of front panel objects in the main program. The discussion that follows elaborates further on items 1 through 4 and shows their LabVIEW implementation examples Item(I) The queue Reference The queue reference in the QSM-PC architecture emulates a command and data messaging pipe-line where the queue accepts data packets added by one or more producer objects and releases these data packets to one consumer object. Figure 7/32 2 elaborates on the queue reference message communication function by showing data packet migration through the queue originating from producer objects and ending at the main consumer object the consumer object loop in item 3 figure 2 includes queue managementⅥs. TheseⅥ s are from labⅥEW s queue palette vi shown in Figure 4 which are used to accomplish various functions such as creating the queue, adding data to the queue, and releasing data from it dds Data t t4 CReates a new caeue Queue E*isTEa Ricun Refererce Q雨国以,是端 as queue配e, E详sUeL obtan queue Enqueue Ee 8D想et Epe他语ti1 to be fc自 element In rort of Preview que,…, Get queue s 9fgq厚 T Prip rity Destroys the Handing Queue Refrence Release queue Enqueue Ela s配g Releases Bata the Q诵 Dequeue Eent Flush Queue Figure 4. LabvIEW s queue palette VIs used in the queued state machine producer consumer programming method. Creating The Queue Reference or Grabing Existing Queue Reference 8/32 The lab vieW queue implementation shown in Figure 3 creates a queue reference of the name: Main Queue using the Obtain Queue Vifrom LabviEW s queue palette; see LabVIEW implementation code in Figure 5. Subsequent and repeated implementation of this same code will grab an existing queue reference of the specified name. this is typically done to give access of queue reference to sub vis which also avoids the need to wire a queue reference to the subVi Qee阳ame一Mne metre RefereR Ce Element Data Type oSTAIE1 T obtain Queue eference Figure 5. LabvIEW code for creating a new queue reference for the queued state machine or grabbing an existing one Two inputs are essential for creating the queue: (a)The Queue Name In this example the queue name is Queue Maini and (b) Data Packet Definition: Shown annotated in Figure 6 is a sample data packet recommended for the queued state machine discussed in this article. This data packet constitutes a cluster containing two pieces of information: ()a type def enumerated constant also 9/32 known as a Function 'STATE constant; and (i a variant ' Data item. this data packet definition means that the resulting queue reference can only carry data elements that conform to this data packet 客T A平A Lists Coaster StaRe M知ces 型 Packages aRy Data for Processing a Hat wan prcess the selected The Respectie State case ER一D3置aake!rQe时 Figure 6. Recommended data packet for queued state machine producer consumer architecture discussed in this artic/e The typedef enumerated constant enlists your chosen names of the state machine cases in the consumer process. each time a command is added to the queue, the enum should be set to the machine s state name which will handle or process the command. Therefore, the type-def state items are like command names that designate which state name contains the relevant code for processing the command Typical function enum state names. INITALIZE DlE ERROR′,and EXI should be included You must ensure that the enum constant is a copy of a typedef-based custom control so that you can add or remove 10/32

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