MsgQueue command group

The MsgQueue command group allows to exchange arbitrary data messages between multiple BRP hosts.

The message exchange is based on a queue that can be accessed by the different BRP hosts. Every host can put a message into the queue (Send command) or can retrieve a message from it (Receive command).

Only one single message can reside in the queue. If a host wants to put a message into a non-empty queue it can only overwrite the queue content if it originates from the host itself. Otherwise a MSGQ_COLLISION_ERR is returned in order to avoid data loss. In this case the message has to be picked up with the Receive command first, which clears the queue. Then a new message can be sent.

The maximum allowed size of a message can be retrieved with GetMsgSize command. A Send/SendReceive command that exceeds this size returns the status code MSGQ_BUFOVERFLOW_ERR.

There are 3 commands for the message handling:

1. Receive: Retrieve a message from the queue
2. Send: Put a message into the queue
3. SendReceive: Put a message into the queue and wait for reception of a new message (combines Send and Receive)

A basic data exchange with alternated sent messages (A => B => A => B => A => B ....) could be implemented like this:

A larger data transfer from A to B consisting of multiples messages without B having to send a response every time could be implemented this way:

Every Send call of A returns as soon as B has picked up the data, so A can directly proceed with the next Send.