MessageLink

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

Initializing the MessageLink Class

A VEXlink is created by using the following constructor:

MessageLink(port, name, linktype, wired)

This constructor uses four parameters:

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 VexlinkType.MANAGER or VexlinkType.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	Optional. Whether or not it is a wired link. Set to True if wired.

# Construct a VEXlink "link" with the MessageLink class.
link = MessageLink(Ports.PORT1, "Link", VexlinkType.MANAGER)

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

Class Methods

is_linked()

The is_linked() method returns the VEXlink’s current status.

Returns: True if the VEXlink is active and connected to the paired Brain. False if it is not.

send()

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

Parameters	Description
message	The message to send.
index	Optional. An integer, such as a port number.
value	Optional. A float.

Returns: The length of transmitted data or None if there is an error.

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

# Send the message 'test' with parameters.
link.send('test', 1, 3.14)

receive()

The receive(timeout) method receives a message from the VEXlink.

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

Returns: The received message or None if there is an error.

received()

The received(callback, arg) method 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.
arg	Optional. A tuple of arguments to pass to the callback function.

Returns: None.

# Define a function message_received()
def message_received():
    # The Brain will print that the message was received by
    # the Message Link on the Brain's screen.
    Brain.screen.print("message received")

# Run message_received() when a message is received.
link.received(message_received)

installed()

The installed() method checks if the VEXlink is connected.

Returns: True if the VEXlink is connected. False if it is not.