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rosrate

Execute loop at fixed frequency

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Description

The rosrate object uses the rateControl (Robotics System Toolbox) superclass to inherit most of its properties and methods. The main difference is that rateControl uses the ROS node as a source for time information. Therefore, it can use the ROS simulation or wall clock time (see the IsSimulationTime property).

If rosinit creates a ROS master in MATLAB®, the global node uses wall clock time.

The performance of the rosrate object and the ability to maintain the DesiredRate value depends on the publishing of the clock information in ROS.

Tip

The scheduling resolution of your operating system and the level of other system activity can affect rate execution accuracy. As a result, accurate rate timing is limited to 100 Hz for execution of MATLAB code. To improve performance and execution speeds, use code generation.

Creation

Syntax

rate = rosrate(desiredRate)
rate = ros.Rate(node,desiredRate)

Description

rate = rosrate(desiredRate) creates a Rate object, which enables you to execute a loop at a fixed frequency, DesiredRate. The time source is linked to the time source of the global ROS node, which requires you to connect MATLAB to a ROS network using rosinit.

example

rate = ros.Rate(node,desiredRate) creates a Rate object that operates loops at a fixed rate based on the time source linked to the specified ROS node, node.

example

Properties

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Desired execution rate of loop, specified as a scalar in hertz. When using waitfor, the loop operates every DesiredRate seconds, unless the loop takes longer. It then begins the next loop based on the specified OverRunAction.

Desired time period between executions, specified as a scalar in seconds. This property is equal to the inverse of DesiredRate.

Elapsed time since construction or reset, specified as a scalar in seconds.

Elapsed time between last two calls to waitfor, specified as a scalar. By default, LastPeriod is set to NaN until waitfor is called for the first time. After the first call, LastPeriod equals TotalElapsedTime.

Method for handling overruns, specified as one of these character vectors:

  • 'drop' — waits until the next time interval equal to a multiple of DesiredPeriod

  • 'slip' — immediately executes the loop again

Workflow of drop and slip overrun handling methods.

Each code section calls waitfor (Robotics System Toolbox) at the end of execution.

Indicator if simulation or wall clock time is used, returned as true or false. If true, the Rate object is using the ROS simulation time to regulate the rate of loop execution.

Object Functions

waitforPause code execution to achieve desired execution rate
statisticsStatistics of past execution periods
resetReset Rate object

Examples

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Open Live Script

Initialize the ROS master and the global node.

rosinit
Launching ROS Core...
Done in 1.1907 seconds.
Initializing ROS master on http://172.30.144.24:59402.
Initializing global node /matlab_global_node_82263 with NodeURI http://dcc796195glnxa64:40363/ and MasterURI http://localhost:59402.

Create a rate object that runs at 1 Hz.

r = rosrate(1);

Start loop that prints iteration and time elapsed. Use waitfor to pause the loop until the next time interval. Reset r prior to the loop execution. Notice that each iteration executes at a 1-second interval.

reset(r)
for i = 1:10
	time = r.TotalElapsedTime;
	fprintf('Iteration: %d - Time Elapsed: %f\n',i,time)
	waitfor(r);
end
Iteration: 1 - Time Elapsed: 0.013034
Iteration: 2 - Time Elapsed: 1.012206
Iteration: 3 - Time Elapsed: 2.007084
Iteration: 4 - Time Elapsed: 3.005331
Iteration: 5 - Time Elapsed: 4.007973
Iteration: 6 - Time Elapsed: 5.017515
Iteration: 7 - Time Elapsed: 6.000958
Iteration: 8 - Time Elapsed: 7.000662
Iteration: 9 - Time Elapsed: 8.001073
Iteration: 10 - Time Elapsed: 9.000875

Shut down the ROS network.

rosshutdown
Shutting down global node /matlab_global_node_82263 with NodeURI http://dcc796195glnxa64:40363/ and MasterURI http://localhost:59402.
Shutting down ROS master on http://172.30.144.24:59402.
Open Live Script

Initialize the ROS master and node.

rosinit
Launching ROS Core...
....Done in 4.1733 seconds.
Initializing ROS master on http://192.168.88.1:51279.
Initializing global node /matlab_global_node_86106 with NodeURI http://ah-avijayar:50550/

node = ros.Node('/testTime');
Using Master URI http://localhost:51279 from the global node to connect to the ROS master.

Create a ros.Rate object running at 20 Hz.

r = ros.Rate(node,20);

Reset the object to restart the timer and run the loop for 30 iterations. Insert code you want to run in the loop before calling waitfor.

reset(r)
for i = 1:30
	% User code goes here.
	waitfor(r);
end

Shut down ROS node.

rosshutdown
Shutting down global node /matlab_global_node_86106 with NodeURI http://ah-avijayar:50550/
Shutting down ROS master on http://192.168.88.1:51279.

Extended Capabilities

Version History

Introduced in R2019b

See Also

(Robotics System Toolbox) |

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