How to create a TCP IP block that runs asynchronously in Simulink with Code Generation?

I have a block in C++ that, every few miliseconds, receives data over TCP/IP. But there might be problems in the sender or the connection, processing delay, etc, and I can't let the rest of the program wait because it is running in real time (it is the Franka Robot Simulink control blocks, more specifically). so if it must, it may use the old data.

How can I configure the block or in some way wrap it so that it doesn't stall the program if it is taking too long receive data?

Thanks in advance.

Answer 1

[Rishav]

Hi Ernest,

To handle the issue of receiving data over TCP/IP without stalling your program, especially in a real-time context like controlling a Franka Robot via Simulink blocks, you can employ a non-blocking or asynchronous approach to data reception. This ensures that your program can continue executing and use the last received data if new data isn't available in time. Here is a strategy for your reference:

1. Use Non-Blocking Sockets

Configure your TCP socket to be non-blocking. This allows your 'recv' call not to wait indefinitely for new data to arrive.

#include <sys/socket.h>
#include <fcntl.h> // For F_SETFL, F_GETFL
#include <errno.h>

int sockfd; // Your socket file descriptor

// Make the socket non-blocking
int flags = fcntl(sockfd, F_GETFL, 0);
if (flags == -1) {
    // Handle error
}
flags = (flags | O_NONBLOCK);
if (fcntl(sockfd, F_SETFL, flags) == -1) {
    // Handle error
}

2. Implement a Data-Checking Loop

Create a loop that periodically checks for new data without blocking. If new data is available, it updates the data used by your program. If not, it continues with the old data.

char buffer[1024]; // Adjust size as necessary
ssize_t receivedBytes;

while (true) { // Main loop
    receivedBytes = recv(sockfd, buffer, sizeof(buffer), 0);
    if (receivedBytes > 0) {
        // Process new data
    } else if (receivedBytes == -1 && errno != EWOULDBLOCK && errno != EAGAIN) {
        // An error occurred, handle it
    }
    // If receivedBytes == -1 and errno == EWOULDBLOCK or EAGAIN, no data was available, continue with old data
    
    // Continue with the rest of your program...
}