the arduino wifi shield
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The Arduino WiFi Shield
Katrina Ellison Geltman March 27, 2014
Arduino UNO R3 Arduino WiFi Shield
Arduino UNO R3 Arduino WiFi Shield
+
vs.
+
vs.
How it Works
Getting set up
In the beginning, you have:
WiFi ShieldComputer WiFi RouterArduino
You set up the basics.
WiFi ShieldComputer WiFi RouterArduino
WiFi driver
Serverobject
You request to connect to the network.
WiFi ShieldComputer WiFi RouterArduino
WiFi driver
Request to connectServerobject
If you’re lucky, you connect successfully.
WiFi ShieldComputer WiFi RouterArduino
WiFi driverConnection successful
Request to connectServerobject
You start your server.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Start TCP server listening onsocket/port
Now it’s listening on a particular port.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
You’re ready to go!
Receiving requests
After setup, everything happens in an event loop.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
At the beginning of the loop, a client object is created using the server’s port & socket.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
Clientobject
The client asks the WiFi shield whether it’s active or not.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectWhat's my state?
If there haven’t been any requests, the client stays inactive.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectInactive
The event loop ends and re-starts.
If there haven’t been any requests, the client stays inactive.
!!
The event loop ends and re-starts. !
I think the client is deleted, but I’m not sure how.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
If a request has been made, the client activates.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectClientobjectConnected!
Request!
Your code asks the client object for whatever data it’s receiving from your computer.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectClientobjectConnected!
Request!
Data?
If there is data, it reads it and processes it.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectClientobjectRead data
Request!
Read data
(This is when your Arduino actually does something)
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectClientobjectRead data
Request!
Read data
Then the event loop ends and the client is deleted.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
!Then the event loop ends and the client is deleted.
(I think)
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
ClientobjectInactive
That’s all good
How it goes wrong
Bad things happen if you disconnect from the network.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
The server doesn’t reconnect properly when the network reconnects.
WiFi ShieldComputer WiFi RouterArduino
Serverobject
Your code loop
We know this from our debugging output.
Socket Port Server Status
Client Status
-1 0 0 0
We know this from our debugging output.
Socket Port Server Status
Client Status
-1 0 0 0
0 80 0 0
We know this from our debugging output.
Socket Port Server Status
Client Status
-1 0 0 0
0 80 0 0Still active!
We know this from our debugging output.
Socket Port Server Status
Client Status
-1 0 0 0
0 80 0 0
No server!
How to fix it
Manually release port & socket
void WiFiServer::disconnect() { WiFiClass::_state[_sock] = -1; WiFiClass::_server_port[_sock] = 0; }
void WiFiServer::disconnect() { WiFiClass::_state[_sock] = -1; WiFiClass::_server_port[_sock] = 0; }
void WiFiServer::disconnect() { WiFiClass::_state[_sock] = -1; WiFiClass::_server_port[_sock] = 0; }
void WiFiServer::disconnect() { WiFiClass::_state[_sock] = -1; WiFiClass::_server_port[_sock] = 0; }
Socket Port Server Status
Client Status
-1 0 0 0
Socket Port Server Status
Client Status
-1 0 0 0
0 80 1 0
It works!
It works!
… trivially
It doesn’t work if a client object has ever
been created
It doesn’t work if a client object has ever
been created
This makes it useless!
It doesn’t work if a client object has ever
been created
usually
This makes it useless!
Memory management?
But available memory does not change from
loop to loop.
I don’t really know C++
Or network programming
So I would love to hear your ideas
But whether or not you can help
Your main takeaway should be
Arduino UNO R3 Arduino WiFi Shield
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