mbed: Triggering interrupt at reception of an UDP broadcast message - udp

Question

I'm trying to trigger an interrupt function each time I receive a broadcast message on a given port of an STM32 board (Nucleo f429zi). The communication protocol I use is UDP and the mbed library is UDPSocket which inherits from Socket.
Does anyone have an idea how to achieve it?
Edit:
Thanks to PeterJ's comment I found an interesting (but deprecated) member function of the class Socket which is called attach(). This method registers a callback on state change of the socket (recv/send/accept).
Since I have an incoming broadcast on the socket, there is no state change in my case (only receiving data, never sending). Is there a way I could use this attach() method to detect every message received?
// Open Ethernet connection
EthernetInterface eth;
eth.connect();
// Create an UDP socket for listening to the broadcast
UDPSocket broadcastSocket;
broadcastSocket.open(&eth);
broadcastSocket.bind(BROADCAST_PORT);
// Function to call when a broadcast message is received
broadcastSocket.attach(&onUDPSocketEvent);
void onUDPSocketEvent(){
printf("UDP event detected\n");
}

Answer 1

attach has been replaced by sigio, but I don't think it's going to do what you want. A nice way would be to spin up a new thread, and use this thread to handle the socket.
void onUDPSocketEvent(void* buffer, size_t size) {
printf("UDP event detected\n");
}
void udp_main() {
// Open Ethernet connection
EthernetInterface eth;
eth.connect();
// Create an UDP socket for listening to the broadcast
UDPSocket broadcastSocket;
broadcastSocket.open(&eth);
broadcastSocket.bind(BROADCAST_PORT);
void* recvBuffer = malloc(1024);
while (1) {
// this blocks until next packet comes in
nsapi_size_or_error_t size = broadcastSocket.recvfrom(NULL, recvBuffer, 1024);
if (size < 0) {
printf("recvfrom failed with error code %d\n", size);
}
onUDPSocketEvent(recvBuffer, size);
}
}
int main() {
Thread t; // can pass in the stack size here if you run out of memory
t.start(&udp_main);
while (1) {
wait(osWaitForever);
}
}
(note that the callback function does not run in an ISR - so not in an interrupt context - but I assume you don't actually want that).
Edit: I have created mbed-udp-ping-pong which shows how to listen for UDP messages on a separate thread.