MAVLINK: Is there a way to associate an ACK to a sent CMD?

[neilyoung]

I'm looking for such a means, but it seems there is no. In case I would like to send a cmd and wait for a certain time for an ack/nack there is a way to associate the cmd sent to the ack received by the cmd ID itself. But what if there are several parallel messages of the same kind on the way?

[aler9]

Hello, what you are referring to is the Command protocol, which is a service built upon Mavlink messages. After you send a command (COMMAND_INT), in order to find the associated response (COMMAND_ACK) in a noisy environment, i think you can use a combination of TargetSystem, TargetComponent and Command as key:

	for evt := range node.Events() {
		if frm, ok := evt.(*gomavlib.EventFrame); ok {
			if ack, ok := frm.Message().(*common.MessageCommandAck); ok {
				if ack.TargetSystem == MY_TARGET_SYSTEM && ack.TargetComponent == MY_TARGET_COMPONENT && ack.Command == COMMAND_COMMAND {
					...
				}
			}
		}
	}

This is somehow error prone with respect to a request-response system in which the request contains a unique ID that can be used as key, but they designed the protocol in this way, and there's no other option right now.

[neilyoung]

You would not believe it, but I came to exactly the same approach. Tnx for confirming.