Hello, I’m Aiden from the Marketing Team.

Today, I would like to introduce the 7th step of PX4 MAVLINK-PYTHON programming: MAV_CMD. This content is registered as the copyrighted property of our QUAD Drone Lab, so please refrain from unauthorized distribution.

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MAV_CMD

OVERVIEW

MAV_CMD Messages is a list of control commands that can be issued to an aircraft in autonomous flight modes.

MAV_CMD primarily consists of COMMAND_INT and COMMAND_LONG types, which are used to send various commands to the drone.

COMMAND_INT Must be used when sending commands that include GPS coordinates or altitude information. This is because it allows for the specification of accurate coordinate frames for position and altitude values.

COMMAND_INT

Field Name	Type	Values	Description
target_system	uint8_t	System ID	Target System ID
target_component	uint8_t	Component ID	Target Component ID (0: All components)
frame	uint8_t	MAV_FRAME	Coordinate system frame
command	uint16_t	MAV_CMD	Command ID (see MAV_CMD enum)
current	uint8_t	0	Not used (set to 0)
autocontinue	uint8_t	0	Not used (set to 0)
param1	float	PARAM1	Specific parameter 1
param2	float	PARAM2	Specific parameter 2
param3	float	PARAM3	Specific parameter 3
param4	float	PARAM4	Specific parameter 4
param5	int32_t	Latitude	Local: x (m) * $10^4$, Global: Lat * $10^7$
param6	int32_t	Longitude	Local: y (m) * $10^4$, Global: Lon * $10^7$
param7	float	Altitude	z position: Global altitude in meters

COMMAND_LONG should be used to send floating-point values in parameters 5 and 6. If these values are sent via COMMAND_INT, they will be truncated into integers.

COMMAND_LONG

Field Name	Type	Values	Description
target_system	uint8_t		System ID
target_component	uint8_t		Component ID (0 : every components)
command	uint16_t	MAV_CMD	Command ID, see MAV_CMD enum
confirmation	uint8_t		0: First transmission of this command. 1-255: Confirmation transmissions
param1	float		Parameter 1 (for the specific command).
param2	float		Parameter 2 (for the specific command).
param3	float		Parameter 3 (for the specific command).
param4	float		Parameter 4 (for the specific command).
param5	float		Parameter 5 (for the specific command).
param6	float		Parameter 6 (for the specific command).
param7	float		Parameter 7 (for the specific command).

COMMAND_INT Sequence

Requests are transmitted from the Ground Control Station (GCS) encoded within a COMMAND_INT message. The drone processes the request and responds promptly with a COMMAND_ACK to indicate the result.

The result (MAV_RESULT) can indicate that the command was accepted
(COMMAND_ACK.result = MAV_RESULT_ACCEPTED), is accepted and in progress (MAV_RESULT_IN_PROGRESS), or was rejected with a specific reason code.

Notably, “MAV_RESULT_ACCEPTED” signifies that the command is valid and the flight stack will attempt to take action; it does not necessarily mean the command has been completed. Most commands return “MAV_RESULT_ACCEPTED” upon initial validation.

COMMAND_ACK.result_param2 may also include additional information regarding the reason for command denial, utilizing command-specific enums.

If an ACK is not received, the GCS retransmits the COMMAND_INT.

COMMAND_LONG Sequence

If a command is dropped, the sender must increment the confirmation field.

Long-Running Commands

Some commands take a long time to execute and cannot be completed immediately. In such cases, the drone transmits a COMMAND_ACK message with COMMAND_ACK.result = MAV_RESULT_IN_PROGRESS to report its status.

The execution progress is indicated in the COMMAND_ACK.progress field as a percentage from 0 to 100 (or 255 if progress information is not available). Once the task is finished, the drone must terminate the sequence by sending a final COMMAND_ACK that contains the ultimate result (e.g., MAV_RESULT_ACCEPTED, MAV_RESULT_FAILED, or MAV_RESULT_CANCELLED).

Long-running tasks can be canceled by sending a COMMAND_CANCEL message. The drone must then cancel the task and complete the sequence by sending a COMMAND_ACK (with COMMAND_ACK.result=MAV_RESULT_CANCELLED).

• If the cancellation is not successful, the drone may continue sending progress updates until the task is complete.
• If the sequence has already been finished or is in an idle state, the cancellation command will be ignored.

The frequency at which the progress message (MAV_RESULT_IN_PROGRESS) is emitted depends on the specific system.

If a timeout is triggered while waiting for a progress or completion update, the GCS must terminate the sequence (returning to an idle state) and notify the user as appropriate.

Only one instance of a specific long-running command can be executed at a time. To restart a long-running task, the existing command must be canceled first!

However, this protocol allows different types of long-running commands to be executed in parallel, provided that the state machine of the receiving flight stack supports it.

Result Verification

COMMAND_ACK ( #77 )

Field Name	Type	Units	Values	Description
command	uint16_t		MAV_CMD	Command ID (of acknowledged command).
result	uint8_t		MAV_RESULT	Result of command.
progress **	uint8_t	%		The progress percentage when result is MAV_RESULT_IN_PROGRESS. Values: [0-100], or UINT8_MAX if the progress is unknown.
result_param2 **	int32_t			Additional result information. Can be set with a command-specific enum containing command-specific error reasons for why the command might be denied. If used, the associated enum must be documented in the corresponding MAV_CMD (this enum should have a 0 value to indicate “unused” or “unknown”).
target_system **	uint8_t			System ID of the target recipient. This is the ID of the system that sent the command for which this COMMAND_ACK is an acknowledgement.
target_component **	uint8_t			Component ID of the target recipient. This is the ID of the system that sent the command for which this COMMAND_ACK is an acknowledgement.

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YOUTUBE Class

재생

This completes our overview of MAV_CMD, a critical component for autonomous drone control. We hope this guide from QUAD Drone Lab helps you build more robust and reliable drone applications.
I will will return with more detailed practical applications and examples related to “Differences between PX4 ‘OFFBOARD’ and ArduPilot ‘GUIDED’ Modes“

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