Call Service

Call service in ROS 2 network

Since R2021b

• 

×

Libraries:
ROS Toolbox / ROS 2

Description

The Call Service block takes a ROS 2 service request message, sends it to the ROS 2 service server, and waits for a response. A ROS 2 service server should be set up somewhere on the network before using this block. Check the available services on a ROS 2 network by executing ros2 service list command, which uses ros2 function. Use ros2svcserver to set up a service server in MATLAB^®.

Specify the name for your ROS 2 service and the service type in the block mask. If connected to a ROS 2 network, you can select from a list of available services. You can create a blank service request or response message to populate with data using the Blank Message block.

Always specify the quality of service (QoS) parameters in the block mask. QoS parameters for this block must be compatible with the service server to send requests and receive responses.

Examples

Call ROS 2 Service in Simulink

Call a service on the ROS 2 network in Simulink^® using the Call Service block and receive a response.

• Open Live Script

Call and Provide ROS 2 Services

Set up service servers to advertise a service to the ROS network. In addition, you will learn how to use service clients to call the server and receive a response.

• Open Live Script

Ports

Input

Req — Request message

nonvirtual bus

Request message, specified as a nonvirtual bus. The request message type corresponds to your service type. To generate an empty request message bus to populate with data, use the Blank Message block.

Data Types: bus

Output

Resp — Response message

nonvirtual bus

Response message, returned as a nonvirtual bus. The response is based on the input Req message. The response message type corresponds to your service type. To generate an empty response message bus to populate with data, use the Blank Message block.

Data Types: bus

ErrorCode — Error conditions for service call

integer

Error conditions for service call, specified as an integer. Each integer corresponds to a different error condition for the service connection or the status of the service call. If an error condition occurs, Resp outputs the last response message or a blank message if a response was not previously received.

Error Code	Condition
0	The service response was successfully retrieved and is available in the Resp output.
1	The connection was not established within the specified Connection timeout.
2	The response from the server was not received.

Dependencies

This output is enabled when the Show ErrorCode output port check box is on.

Data Types: uint8

Parameters

Main

Source — Source for specifying service name

Select from ROS network | Specify your own

Source for specifying the service name:

• Select from ROS network — Use Select to select a service name. The Name and Type parameters are set automatically. You must be connected to a ROS 2 network.

• Specify your own — Enter a service name in Name and specify its service type in Type. You must match a service name exactly.

Name — Service name

character vector

Service name, specified as a character vector. The service name must match a service name available on the ROS service server. To see a list of valid services in a ROS 2 network, see ros2.

Type — Service type

character vector

Service type, specified as a character vector. Each service name has a corresponding type.

Connection timeout — Timeout for service server connection

5 (default) | positive numeric scalar

Timeout for service server connection, specified as a positive numeric scalar in seconds. If a connection cannot be established with the ROS service server in this time, then ErrorCode outputs 1.

Show ErrorCode output port — Enable error code output port

on (default) | off

Check this box to output the ErrorCode output. If an error condition occurs, Resp outputs the last response message or a blank message if response was not previously received.

Quality of Service (QoS)

History — Mode of storing requests in the queue

Keep last (default) | Keep all

Determines the mode of storing requests in the queue. If the queue fills with requests waiting to be processed, then old requests will be dropped to make room for new. If set to Keep last, the queue stores the number of requests set by the Depth parameter. If set to Keep all, the queue stores all requests up to the MATLAB resource limits.

Depth — Size of the request queue

1 (default) | positive scalar

Number of requests stored in the request queue when History is set to Keep last.

Reliability — Delivery guarantee of requests

Reliable (default) | Best effort

Affects the guarantee of request delivery. If Reliable, then delivery is guaranteed, but may retry multiple times. If Best effort, then attempt delivery and do not retry. Reliable setting is recommended for services.

Durability — Persistence of requests

Volatile (default) | Transient local

Affects persistence of requests, which allows late-starting servers to receive the number of old requests specified by Depth. If Volatile, then requests do not persist. If Transient local, then the block will persist most recent requests.

Deadline — Maximum amount of time allowed between sending service request and receiving response

Inf (default) | positive scalar

Maximum amount of time allowed between sending a service request and receiving a response, specified as a positive scalar. The Deadline QoS parameter of service servers receiving request from the block must be less than or equal to the value of this parameter.

The default value is Inf which implies that after the service client sends a request, it can wait for an infinite period of time before receiving response to that request.

Note

The quality of service settings must be compatible between service servers and clients for a connection to be made.

Lifespan — Length of time a service request is considered valid

Inf (default) | positive scalar

Length of time a service request is considered valid, specified as a positive scalar. This value determines the time for which the service requests sent are stored in the queue.

The default value is Inf which implies that a service request sent by service client is considered valid for infinite period of time.

Note

The quality of service settings must be compatible between service servers and clients for a connection to be made.

Liveliness — Level of liveliness reporting provided by the block and expected from service server

automatic (default)

Level of liveliness reporting provided by the block and expected from the connected service server, specified as automatic.

Liveliness set to automatic implies that after the block receives a service response from the connected server, the block considers that server to be alive for another Lease Duration.

Note

The quality of service settings must be compatible between service servers and clients for a connection to be made.

Lease Duration — Maximum amount of time before which connected service server has to assert liveliness

Inf (default) | positive scalar

Maximum amount of time before which the connected service server has to assert liveliness, specified as a positive scalar.

The default value is Inf which implies that the service server connected to the client can assert liveliness for infinite period of time.

Note

The quality of service settings must be compatible between service servers and clients for a connection to be made.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2021b