ParallelismDay 12

Computer Programming through Robotics

CPST 410

Summer 2009

7/1/09 Harry Howard, CPST 410, Tulane University

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Course organization

Course home page (http://robolab.tulane.edu/CPST410/)

Lab (Newcomb 442) will be open for practice with 3-4 Macs, but you can bring your own laptop and all robots.

Parallelism

Beams vs. tasks

Multiple beams in NXT-G

Open the Mindstorms app.

7/1/09 Harry Howard, CPST 410, Tulane University

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Parking

Tribot, drive straight forward for 1 rotations, then drive forward turning to the right for 1 rotations, then back up for 2 seconds. When you are finished, display a locked lock for 3

seconds and reset the screen.

While you are backing up, play a warning sound (! hydraulic 03).

ParkBot.rbt, part 1

The second part

How do you make Tribot play a sound while it backs up?

You need to pull out a new sequence beam.Hold down shift key to pull out new beam.

Also, Tribot must play the sound continuously.

The next program is a good first try.

7/1/09 Harry Howard, CPST 410, Tulane University

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ParkBot.rbt, Part 2, first try

A problem

The problem is that the sound does not necessarily stop when Tribot stops backing up.

To do so, you have to ensure that the loop breaks when the backup motion has finished.

This can only be done with a logical variable.

ParkBot.rbt, Part 2, final try

Parallel beams = tasks in NXC

Close the Mindstorms app,

and open BricxCC.

7/1/09 Harry Howard, CPST 410, Tulane University

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Task overview

An NXC program consists of at most 256 tasks, each of which must have a unique name.

There must always be a task named main, since this is the first task to be executed.

Another task will be executed when a running task tells it to be executed;if it is explicitly scheduled in main.

Tasks run simultaneously unless otherwise specified by scheduling statements.

7/1/09 Harry Howard, CPST 410, Tulane University

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Task syntax and usage

task name(){

“statements”

}Start a task by means of the function:

StartTask(task)Example

StartTask(sound); // start the sound task

7/1/09 Harry Howard, CPST 410, Tulane University

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Parallelism

Even though tasks run simultaneously, the action performed by the task has to be programmed to run continuously.So always put the action within an endless while loop:

my_task(){

while(true){// do something}

}

7/1/09 Harry Howard, CPST 410, Tulane University

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Now translate the parking program to NXC

7/1/09 Harry Howard, CPST 410, Tulane University

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Scheduling tasksp. 159

Since tasks execute simultaneously, it takes special functions to schedule them:Precedes(task1, task2, …, taskN);Follows(task1, task2, …, taskN);ExitTo(task);

UsagePrecedes and Follows should only be used once within

a task, preferably at its beginning.If multiple tasks declare that they precede or follow the

same task, then they execute simultaneously.

7/1/09 Harry Howard, CPST 410, Tulane University

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Halting the programp. 159

Halt the program by stopping all tasks:Stop(condition);StopAllTasks;

UsageThe program halts after either command, so

everything following them is ignored.

7/1/09 Harry Howard, CPST 410, Tulane University

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Next time

E-mail me your final project ideally, by the end of class on Monday;or by Tuesday evening.

Drop off your robot at Newcomb 302, between 9am and 5 pm, ore-mail me to make an appointment for some

other time.