workshop 4 of 7

Workshop 4 of 7

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Today's Topics

Review of Workshop 3

Sequence Structure Timing State Machine

Review Question 1

How many times must a For Loop iterate? A While Loop?

a) 0,0

b) 1,0

c) 0,1

d) 1,1

Review Question 1

How many times must a For Loop iterate? A While Loop?

a) 0,0

b) 1,0

c) 0,1d) 1,1

Review Question 2

True or False?The value passed to the case selector terminal determines which case will execute.

Review Question 2

True or False?The value passed to the case selector terminal determines which case will execute.

TRUE

Review Question 3

A “hollow” output tunnel will appear on the edge of a case structure because…?

a) the wrong data type is wired to it

b) there is not a wire leading away from it

c) one or more cases do not have a wire leading to it

Review Question 3

A “hollow” output tunnel will appear on the edge of a case structure because…?

a) the wrong data type is wired to it

b) there is not a wire leading away from it

c) one or more cases do not have a wire leading to it

Review Question 4

Which of the following statements about Auto-indexing are true? (multiple answers possible)

a) When auto-indexing is enabled on an output tunnel, only one element can be passed out of the tunnel.

b) When auto-indexing is enabled on an input tunnel, only one element can be passed out of the tunnel

c) When auto-indexing is enabled on an output tunnel, the entire array is passed out of the tunnel

d) When auto-indexing is enabled on an input tunnel, the entire array is passed out of the tunnel

Review Question 4

Which of the following statements about Auto-indexing are true? (multiple answers possible)

a) When auto-indexing is enabled on an output tunnel, only one element can be passed out of the tunnel.

b) When auto-indexing is enabled on an input tunnel, only one element can be passed out of the tunnel

c) When auto-indexing is enabled on an output tunnel, the entire array is passed out of the tunnel

d) When auto-indexing is enabled on an input tunnel, the entire array is passed out of the tunnel

Review Question 5

The value of Result when the VI below finishes will be:

a) 15

b) 18

c) 22

d) 28

Review Question 5

The value of Result when the VI below finishes will be:

a) 15

b) 18c) 22

d) 28

Review Question 1

True or False?

You must have at least one case in a Disable Diagram that is enabled.

Review Question 1

True or False?

You must have at least one case in a Disable Diagram that is enabled.

TRUE

Review Question 2Match the following:

a) Event Filter Node

b) Notify Event

c) Filter Event

d) Event Data Node

• attached to the inside left border of each event case; identifies the data LabVIEW provides when an event occurs.

• attached to the inside right border of filter event cases; identifies the subset of data available that the event case can modify

• an indication that a user action has already occurred, such as when the user has changed the value of a control

• inform you that the user has performed an action before LabVIEW processes it, which allows you to customize how the program responds to interactions with the user interface

Review Question 2

Match the following:

a) Event Filter Node

b) Notify Event

c) Filter Event

d) Event Data Node

• attached to the inside left border of each event case; identifies the data LabVIEW provides when an event occurs.

• attached to the inside right border of filter event cases; identifies the subset of data available that the event case can modify

• an indication that a user action has already occurred, such as when the user has changed the value of a control

• Informs you that the user has performed an action before LabVIEW processes it, which allows you to customize how the program responds to interactions with the user interface

Review Question 3

Which of the following is true about the Event Structure?

a) An event structure will sleep while waiting for an event to occur

b) An even structure can process multiple events simultaneously

c) It is a good idea multiple event structures within a block diagram

d) Event structures are often used within a while loop

Review Question 3

Which of the following is true about the Event Structure?

a) An event structure will sleep while waiting for an event to occur TRUE

b) An even structure can process multiple events simultaneously FALSE

c) It is a good idea multiple event structures within a block diagram FALSE

d) Event structures are often used within a while loop TRUE

Flat Sequence Structure Executes each frame beginning with the left-most frame

and ending with the right-most frame The previous frame must complete before the next frame

executes Data can be passed out of or between frames using tunnels Once the sequence begins, it cannot be stopped

1st 2nd 3rd

Stacked Sequence Structure

Stacks each frame so you see only one frame at a time Executes frame 0, then frame 1, etc. until the last frame

executes Returns data only after the

last frame executes To transfer data from frame

to frame, a Sequence Local must be created (right-click » Add Sequence Local)

• Once the sequence begins, it cannot be stopped

Sequence Local

Timing Functions

• Control or measure the frequency at which a loop executes• Provide the processor with time to complete other tasks,

such as processing the user interface• Uses the operating system millisecond clock

Wait Function

• Waits the specified number of milliseconds.• If 0 is wired to it, the current thread is forced to yield

control of the CPU • Uses the operating system millisecond clock

Wait Function- example cases

10 ms 20 ms 30 ms

Wait

Other code (running in parallel with Wait VI)

• Loop would go on to next iteration after 10 ms, because the only thing that happens in each iteration is wait 10 ms

• Loop would go to next iteration after 10 ms or more depending on amount of time the subVI takes.

• If subVI takes >10 ms, loop goes as soon as subVI is done

• If subVI takes <10 ms , loop goes at 10 ms mark.

Moment next loop iteration can begin

Wait Until Next Millisecond Multiple Function

• Waits until a multiple of the millisecond value wired in• Provide the processor with time to complete other

tasks, such as processing the user interface• Uses the operating system millisecond clock

Wait Until Next Millisecond Multiple Function

10 ms 20 ms 30 ms

• Loop would go on to next iteration after 10 ms, because the only thing that happens in each iteration is wait 10 ms and 10ms is the first multiple of 10

• Loop would go to next iteration after 10 , 20, 30, or a greater multiple of 10 ms depending on amount of time the subVI takes.

• If subVI takes <10 ms , loop goes at 10 ms mark.

• If subVI takes 16 ms, then the loop goes at 20 ms.

• If subVI takes 22 ms, then the subVI goes at 30 ms.

Wait

Other code (subVI)

Comparison of Timing Functions

10 ms 20 ms 30 ms

Other code (running in

parallel with waits)

Moment next loop iteration can begin

Red represents times when Wait functions are NOT restricting

Demonstration: Comparing the Timing Functions

VI Timing Types• Execution Timing

• Provides the design pattern with a function that specifically allows the processor time to complete other tasks

• In some cases, a Wait function is not necessary

• Use of Timeout inputs can provide execution timing

• Software Control Timing

• Timing (pauses, waits, time checks) you put in place to make the code execute after a certain amount of time.

• Example:• If you must acquire data for 5 minutes, you could remain in the acquisition state until

the 5 minutes elapses. However, during that time you cannot process any user interface actions such as stopping the VI. To process user interface actions, you must implement timing (checking if 5 min has passed since the start of acquisition) so that the VI continually executes for the specified time

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Software Control Timing

Execution TimingVI Timing

State Machine Intro: Scenario

Want to create a program that does the following:

1. Reads a voltage

2. Tells user to turn on power supply

3. Read the voltage again now that power is on

4. Tell the user to turn off the power.

Programming Designs: Sequential

Sequential Programming

Sequential Programming

Sequential Programming

Sequential Programming

• What if you need to change the order of the sequence?

• What if you need to repeat one item in the sequence more often than the other items?

• What if some items in the sequence execute only when certain conditions are met?

• What if you need to stop the program immediately, rather than waiting until the end of the sequence?

State Machines

• Implements a state diagram.

• Programmatically determine which state is next- Different action if a

quarter was inserted compared to return change requested

• A state machine consists of a set of states and a transition function that maps to the next state

• Each state can lead to one or multiple states or end the process flow

While Loop

Case StructureShift Register

State Machine

Enum

• State Functionality Code: • this state was entered to perform

what function?

• Transition Code: • which state is next?

State Machine: Transition Code

Demonstration: Execution of a State Machine

General VI Three phases: Start-up, Main Application, and Shut-

down

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Design Patterns: Single Loop

General VI

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Single Loop Design Pattern: in LabVIEW

Single Loop Design Pattern

State MachineUsually has a start-up and shut-down state, but also

contains other states

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Single Loop Design Pattern

State Machine

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Parallelism Parallelism: executing multiple tasks at the same time

Use case:• Need to acquire data very quickly, process it and save it to file.• If you do each step in a linear fashion and try to acquire all the data

before processing, then you may run out of memory before processing begins.

• If you do “sets” of steps (acquire, process, save, repeat), then you are missing the data points when the processing and saving are going on.

• If only you could acquire, process, and save in parallel….good news, you can!

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Multiple Loop Design Pattern

Parallel Loop

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Multiple Loop Design PatternProducer/Consumer

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Multiple Loop Design PatternMaster/Slave: a type of Producer/Consumer

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• uses notifiers to allow loops to run at different rates

NotifiersPros:

• Both loops are synchronized to the master loop—the slave loop only executes when the master loop sends a notification

• You can use notifiers to create globally available data, making it possible to send data with a notification

• Using notifiers creates efficient code—there is no need to poll to determine when data is available from the master loop

Cons:• Notifiers do not buffer data.

• If the master loop sends another piece of data before the first piece of data has been read by the slave loops, that data is overwritten and lost.

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Queues

• Queues are similar to notifiers, except that a queue can store multiple pieces of data

• By default, queues work in a FIFO (first in, first out) manner

• Use a queue when you want to process all data placed in the queue

• Use a notifier if you only want to process the current data

• Use the Queue Operations functions to create a queue for communicating data between sections of a block diagram or from another VI.

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Producer/Consumer with Queues

Data type here determines the data type that can be placed in the queue

Demonstration: Queues in Action

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Producer/Consumer with Queues and Events

• Efficiently responds asynchronously to the user interface

Notifier vs. Queue Review

Tool Function When to use

Notifier - sends alert to helps control timing of parallel loops- can transfer data between loops- data NOT buffered (lossy)

- have a parallel loops that are running at different rates and 1+ loop is dependent on another- want to transfer data from one loop to another

Queue - helps control timing of parallel loops - transfers data between loops - buffers data to be transferred (FIFO)

- have a parallel loops that are running at different rates and 1+ loop is dependent on another- want to transfer ALL data from one loop to another

Work on a Game!

Complete Homework 4

CLAD Questions 4

Email to mst.labview@gmail.com

Homework