TCP-client-server
A pair of programs to test two Arduino Nano 33 IoT boards, one acting as TCP client and the other one as TCP server
Both programs function as a state machine, with a variable 'connectionState' controlling execution. WiFi connection and client connection state is constantly checked. There are no while loops, no calls to 'delay()' etc. All timeouts controlled by timer.
Server-side states
enum ConnectionState_type {
conn_0_wifiConnectNow, // attempt to connect wifi
conn_1_wifiDelayConnection, // waiting for next attempt to connect wifi (after timeout)
conn_2_wifiConnected, // attempt to connect to client
conn_3_clientDelayConnection, // wait for next attempt to connect to client (after timeout)
conn_4_clientConnected, // server connected to client (waiting for client request)
conn_5_requestReceived, // client request received: send server response
conn_6_stopClientNow, // stop client connection
conn_7_report // send info about last connection cycle to serial monitor
};
Client-side states
enum ConnectionState_type {
conn_0_wifiConnectNow, // attempt to connect wifi
conn_1_wifiDelayConnection, // waiting for next attempt to connect wifi (after timeout)
conn_2_wifiConnected, // attempt to connect to server
conn_3_clientDelayConnection, // waiting for next attempt to connect to server (after timeout)
conn_4_clientConnected, // client connected to server (may send request to server)
conn_5_requestSent, // client request sent to server: wait for server response
conn_6_stopClientNow, // stop connection to server
conn_7_report // send info about last connection cycle to serial monitor
};
Server-side main loop (client side is similar)
void loop() {
// code contains no calls to 'delay()', all delays and timeouts controlled by timer
// variable 'connectionState' controls proper sequencing of tasks in these procedures:
connectToWiFi(); // if currently not connected to wifi (or connection lost): connect
connectToClient(); // if a client is available but not connected: connect
assembleClientRequest(); // read one incoming character of client request, if available
sendResponseToClient(); // when client request is complete, send response to client
stopTCPconnection(); // stop connection to client (when client side disconnected or after time out)
lastConnectionReport(); // send info about last connection cycle to serial monitor
// not controlled by state but by time
heartbeat(); // 1 second heartbeat: print current connection state
}
Both server and client print status information to the serial port (see excel workbook, attached). In addition, the server-side code outputs signals on pins 10 to 12 that are displayed on an oscilloscope, enabling to see what is actually happening and when.
Normal flow
client connects server notices client and connects client sends a 'client request' (a 7-digit number) followed by CRLF server reads request and echoes it as a 'server response' to the client client stops server detects client stopped and stops as well
Time outs
server and client time out if data is not received within 10 seconds these time outs can be modified (defined as constants)
Delays
if a WiFi connection attempt fails, next attempt will happen after a delay (using the state machine logic) server side: after each client.stop(), a small delay is applied before next connection attempt (using the state machine logic) client side: a small delay is applied between two connection attempts OR between a client.stop() and a next connection attempt delay timings can be modified (defned as constants) Client connection delay is quite short, but increasing it does not solve the issues.
Note
In relation to these tests, I filed a bug report "Nano 33 IoT server hangs OR stops making connection with client" (arduino/Arduino#11421)