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MAVLink Deserializer

Convert serialized uint8 MAVLink data stream to Simulink nonvirtual bus

Since R2020b

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Libraries:
UAV Toolbox / MAVLink

Description

The MAVLink Deserializer block receives a uint8 buffer and decodes the buffer for MAVLink messages. Once the block receives the MAVLink message for the selected MAVLink message type, the block outputs a Simulink® nonvirtual bus representing a MAVLink packet containing the Message ID, System ID, Component ID, Sequence, and Payload information corresponding to the selected MAVLink message type.

At each simulation step, the block decodes the input uint8 buffer and retrieves the MAVLink messages that are received after decoding. If a new message for the selected MAVLink message type has been received, the block retrieves that message from the list of received messages and converts it to a Simulink nonvirtual bus signal.

The MAVLink decoding logic in the block takes care of scenarios where a MAVLink packet has been received partially from a communication channel. The MAVLink Deserializer block internally stores the current state of parsing and resumes decoding from the previous step when the new buffer has been received over the communication channel. If the complete MAVLink packet has been received and the received checksum matches the computed checksum for the received bytes, then this indicates that a MAVLink message has been received. Storing the state of parsing ensures that the block can decode the MAVLink packets received in multiple parts.

By default, the block outputs the latest received MAVLink message for the selected MAVLink message type (if received). This behavior can be changed by selecting Queue Messages in output parameter. In this case, all the received MAVLink messages for the desired type are queued and at each Simulation step, the block outputs the oldest message.

Ports

Input

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The uint8 byte stream that contains serialized MAVLink packets. The byte stream is usually received over a communication channel such as UDP, TCP, or Serial. At each sample time, the communication channel receives data and returns a byte stream that contains one or more MAVLink packets. The byte stream can also return a MAVLink packet partially in over multiple sample times. This input port accepts variable-length signals.

Data Types: uint8

Optional input port to include the length of valid MAVLink data. To enable this port, select the Input data stream length is available parameter. Use this option when you know the exact length of the valid MAVLink data in the data stream.

This option is useful when you have a communication channel receive peripheral that outputs partially received data that contains trailing zeros. Such peripherals also output the length of the actual number of valid data bytes received. You can connect the length output of the peripheral directly with the Length input port of MAVLink Deserializer block, so that trailing zeros in the input byte stream do not affect the decoding logic.

Data Types: uint16

Output

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New MAVLink message indicator returned as a logical. A value of 1 indicates that a new message is available since the last sample was received by the block. This output can be used to trigger subsystems to process new messages received from the MAVLink Deserializer block.

Data Types: Boolean

MAVLink packet, returned as a nonvirtual bus. The type of Payload in the MAVLink packet is a Simulink bus corresponding to the MAVLink message specified in the MAVLink message type parameter. The block outputs blank messages until it receives a message on the message name that you specify. The Msg port outputs this new message. If a new message is not available, it outputs the last received MAVLink message. If a message has not been received since the start of the simulation, Msg port outputs a blank MAVLink message.

Data Types: bus

Parameters

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Main

Source for specifying the MAVLink message definition XML name, specified as one of the following:

  • Select from standard MAVLink dialects - Use this option to select a definition XML among the 12 commonly used message definition XML names listed in the MAVLink dialect parameter.

  • Specify your own - Enter an XML name in the text box that appears for the MAVLink dialect parameter.

MAVLink message definition file (.xml) to parse for MAVLink messages, specified as a string.

If the MAVLink dialect source parameter is set to Select from standard MAVLink dialects, you need to select a message definition among the available message definition names from the dropdown list.

If the parameter MAVLink dialect source parameter is set to Specify your own, you need to specify the message definition file (.xml) that is on the current MATLAB path, or you can provide the full path of the XML file.

MAVLink protocol version that the block uses to serialize and deserialize the MAVLink messages.

MAVLink message, specified as a string. Click Select to select from a full list of available MAVLink messages. The list varies based on the values that you selected for MAVLink dialect and MAVLink version parameters.

Data Types: string

Advanced

When you select this option, the MAVLink Deserializer block provides an additional input port called Length. This input port can be used to pass the actual length of MAVLink data (if known) in the input byte stream. The input byte stream is cropped for this length.

This option is useful when you have a communication channel receive peripheral that outputs partially received data that contains trailing zeros. Such peripherals also output length of the actual number of valid data bytes received. You can connect the length output of the peripheral directly to the Length input port of MAVLink Deserializer block so that trailing zeros in the input byte stream do not affect the decoding logic.

Select this option to filter the received MAVLink messages for the System ID value mentioned in the System ID parameter. This option helps you to filter the received messages by both System ID and Component ID.

Specify the System ID value to use while filtering the decoded MAVLink messages. The block outputs the received MAVLink messages whose System ID matches the specified value and whose Message ID matches the MAVLink message (selected in the MAVLink Message type parameter).

Dependencies

To enable this parameter, select Filter Output MAVLink messages by System ID.

Select this option to filter the received MAVLink messages for the both the System ID and the Component ID mentioned in the System ID and Component ID parameters, respectively.

Dependencies

This parameter appears only if you select the Filter output MAVLink messages by System ID parameter.

Specify the Component ID value to use while filtering the decoded MAVLink messages. The block outputs those received MAVLink messages whose System ID and Component ID values match the specified values in the System ID and Component ID parameters, respectively, and whose Message ID matches the MAVLink message (selected in the MAVLink Message type parameter).

Dependencies

To enable this parameter, select Filter Output MAVLink messages by Component ID.

Select this option to output messages using the first-in-first-out pattern. If you do not select this option, the MAVLink Deserializer block outputs the latest received MAVLink message for the selected MAVLink message type (and with matching System ID and Component ID if those parameters are selected) at each simulation step. If more than one message matches the given parameters that are received in a simulation step, the latest message is passed as output, and the rest are discarded. You can reverse this behavior by selecting this option.

When you select this parameter, the behavior of the MAVLink Deserializer block at each simulation step is:

  • The block stores the decoded MAVLink messages matching the selected MAVLink message type (and matching System ID and Component ID if the those parameters are selected) in a queue. If there are no messages among the received messages that match the required parameters, no messages are queued.

  • If the queue is not empty, the first message in the queue is sent as an output first, and the signal at IsNew port is set to 1.

Selecting the Queue MAVLink messages in output parameter makes the Number of messages to be queued parameter visible. You can fix the size of the queue by setting the value of this parameter.

Specify the size of the queue to be used to store the received MAVLink messages matching the desired parameters.

Dependencies

To enable this parameter, select Queue MAVLink messages in output.

Tips

To speed up the conversion of the received serialized data, it is recommended that you apply the following settings in the communication channel receive block:

  • Read the data at the highest rate possible to ensure that no packets are dropped. Use the IsNew output of MAVLink Deserializer along with the logic to use MAVLink messages to know if the output of the block is a new message or not.

  • If the receive block outputs any number of bytes that are received irrespective of the data size requested (partial receive), mention the data read size as a large number and use the length of actual number of bytes received as an input to MAVLink Deserializer block (use the Length input port).

Extended Capabilities

Version History

Introduced in R2020b

See Also

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