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.
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