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Unresolved Solved: blocking connection.recv(255) doesn't allow asynchronous serial send/ tcp receive.
socket.accept() returns a tuple, consisting of the a socket and an address. So in your script, the variable connection is of type "socket". Which can set to non-blocking mode by connection.setblocking(False).
The Script connect_jsi_main.py serves as initializer on setup (main.py) to establish a WLAN-connection before opening a socket server by executing of script Serial_Bridge_ok.py.
See: select with socket and how can non-blocking socket instances be implemented