message_link

What is a Message Link?

VEXlink enables an EXP Brain to communicate with another EXP Brain, allowing for point-to-point connections and the creation of communication meshes between multiple robots. It supports both wireless and wired communication, with wired connections recommending a modified smart cable to prevent power routing issues. For wireless communication, each robot needs a V5 Robot Radio connected to a Smart Port, and the VEXlink Radio can be used alongside a V5 Controller’s VEXnet radio, which should be connected to the highest numbered Smart Port to avoid conflicts.

The message_link class within VEXlink facilitates sending simple messages, such as “play” and “stop,” with minimal data to the connected robot.

Initializing the message_link Class

A VEXlink is created by using the following constructor:

The message_link constructor creates a message_link object in the specified Port, with the specified ID and linktype, and sets the wired flag to the specified value.

Parameter	Description
port	A valid Smart Port that the VEXlink Radio is connected to.
name	The name of this link. It is recommended that this unique string is long enough that when hashed by vexos it will create a unique ID. A bad link name would be something generic such as “vexlink” as it may be used by another team.
linktype	The type of link, either linkType::manager or linkType::worker. This information is used to correctly configure the radio and also determines available bandwidth for transmission and reception. A manager robot has double the available bandwidth (1040 bytes/second) to send information to the worker robot (520 bytes/second).
wired	Whether or not it is a wired link. Set to true if wired.

// Construct a VEXlink "link" with the message_link class.
message_link link = message_link(PORT1, "link", linkType::manager);

This link object will be used in all subsequent examples throughout this API documentation when referring to message_link class methods.

Class Methods

send()

This method is called in the following ways:

The send(message) method sends a message through the Message Link.

Parameters	Description
message	The message to send.

Returns: An integer representing the length of transmitted data.

// Send the message 'test' with no parameters.
link.send('test');

The send(message, value) method sends a message through the Message Link.

Parameters	Description
message	The message to send.
value	An float representing the ID of the message.

Returns: An integer representing the length of transmitted data.

The send(message, index, value) method sends a message through the Message Link.

Parameters	Description
message	The message to send.
index	An integer representing the port the receiving Message Link is connected to.
value	An float representing the ID of the message.

Returns: An integer representing the length of transmitted data.

receive()

The receive(timeout) command receives a message from the Message Link.

Parameters	Description
timeout	The timeout duration for receiving the message in milliseconds before the function returns.

Returns: The received message.

received()

The received(callback) command registers a callback function for when a message is received. If the message is omitted then the callback function will be called for all messages.

Parameters	Description
callback	The callback function to be called when a message is received.

Returns: An instance of the event class.