[FreeRTOS+TCP API Reference]
BaseType_t FreeRTOS_listen( Socket_t xSocket, BaseType_t xBacklog );
Places a TCP socket into a state where it is listening for and can accept incoming connection requests from remote sockets.
By default a new socket (a child socket) will be created to handle any accepted connections. The new socket will be returned by FreeRTOS_accept(), and can be used immediately. The child socket inherits all the properties from the parent socket.
Optionally the FREERTOS_SO_REUSE_LISTEN_SOCKET parameter can be used with a call to FreeRTOS_setsockopt() to configure the parent socket to handle any accepted connections itself – without creating a child socket for this purpose. This is a useful way to save resources when the socket will only handle a single connection at a time. For example, if the socket is used to implement a telnet server that only permits one simultaneous connection.
The handle of the socket being placed into the Listening
state. The socket
must have already been created using a call to
and bound to a port number using a call to
In the default case where a new socket is created for each
new connection the backlog value puts a limit on the
number of simultaneously connected clients.
If the the socket was successfully placed into the listening state then 0 is returned.
If xSocket is not a valid TCP socket then then -pdFREERTOS_ERRNO_EOPNOTSUPP is returned.
If xSocket is not in bound but closed state then -pdFREERTOS_ERRNO_EOPNOTSUPP is returned.
Note that, because FreeRTOS does not implement errno, the behaviour in the presence of an error is necessarily different to that of connect() functions that are fully compliant with the expected Berkeley sockets behaviour.
See the “Creating, configuring and binding a TCP server socket” source code example in the “Creating Configuring and Binding TCP Client and Server Sockets” section of the FreeRTOS+TCP networking tutorial pages.