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WebSocket Subscribe

Subscribe to the JSON data received by a WebSocket server

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  • Library:

  • Simulink Support Package for Raspberry Pi Hardware / Network

  • Raspberry Pi WebSocket Subscribe icon

Description

The WebSocket Subscribe block subscribes to the data received by a WebSocket server identified by an IP address and a port. The received data must be in JavaScript Object Notation (JSON) format, which can be interpreted by a WebSocket client to manipulate the data.

WebSocket JSON Data

This figure shows the signals in JSON format with a unique block label.

WebSocket JSON Data

Ports

Output

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The data received by the WebSocket server, specified as a row vector.

The block provides an option to add up to 10 Out ports to obtain signal data, with each signal being an N-by-1 vector. N is the number of data points in a signal.

Example: [1.5,3]

Dependencies

To enable the port, specify the total number of output signals in the Number of outputs parameter. When you specify Number of outputs, the block generates equal number of output ports. For example, if you specify Number of outputs as 4, the block generates four output ports.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

The block outputs the status indicating the validity of the received data.

The status is:

  • 1: Valid data

  • 0: Received data is empty or is of invalid JSON format

  • -1: Mismatch in number of data fields

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Parameters

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The IP address of the WebSocket server on which the JSON data is hosted.

The port number on the WebSocket server on which the JSON data is hosted.

Note

To avoid any resource conflicts, the Server IP address and Server Port parameters of all the WebSocket Subscribe blocks in a Simulink® model must be unique.

Specify the properties of the data using the Block Parameters dialog box or from a JSON file.

  • Mask Dialog –– Specify the total number of signal data using the block parameters dialog box. The block generates output ports that are equal in number to the total number of signals specified. You must also specify data size and data type of each signal using the dialog box.

  • JSON file –– If you have a JSON file that contains the signal data, upload the file by clicking the Browse button. On successfully uploading the file, the block generates output ports that are equal in number to the data signals in the specified file. The data size and data type of each signal is inherited from the file.

Specify the total number of output signals received by the WebSocket server. When you specify a value in this parameter, the block generates output ports that are equal in number to the value specified in this parameter. For example, if you specify Number of outputs as 4, the block generates four output ports.

Dependencies

To enable the parameter, set the Specify output info via parameter to Mask Dialog.

Specify the total number of data points in an output signal.

Dependencies

To enable the parameter, set the Specify output info via parameter to Mask Dialog.

The data type of the output signal.

Dependencies

To enable the parameter, set the Specify output info via parameter to Mask Dialog.

Click the Browse button to choose a JSON file that contains the signal data. On successfully uploading the JSON file, the block generates output ports that are equal in number to the data signals in the specified file. The data size and data type of each signal is inherited from the file.

Dependencies

To enable the parameter, set the Specify output info via parameter to JSON file.

Specify how often the block receives the data from the WebSocket server. When you specify Sample time as -1, the block inherits its sample time based on the context of the block within the model.

Version History

Introduced in R2020a

See Also

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