Ethernet - UDP

Set up LWIP according to the previous note

STM32 UDP Server Example – lwIP UDP SERVER SetupControllersTech®

#include "lwip/udp.h"


void UDP_receive_handler(void *arg, struct udp_pcb *udp_control, struct pbuf *packet, const ip_addr_t *addr, u16_t port) {
  struct pbuf *tx_buf;

  // Get the IP of the Client
//  char *remote_ip = ipaddr_ntoa(addr);

  char buf[100];

  int len = sprintf(buf,"Hello %s From UDP SERVER\n", (char*)packet->payload);

  // allocate pbuf from RAM
  tx_buf = pbuf_alloc(PBUF_TRANSPORT, len, PBUF_RAM);

  // copy the data into the buffer
  pbuf_take(tx_buf, buf, len);

  // Connect to the remote client
  udp_connect(udp_control, addr, port);

  // Send a Reply to the Client
  udp_send(udp_control, tx_buf);

  // free the UDP connection, so we can accept new clients
  udp_disconnect(udp_control);

  // Free the buffers
  pbuf_free(tx_buf);
  pbuf_free(packet);
}

void UDP_init_server() {
   /* 1. Create a new UDP control block  */
   struct udp_pcb *udp_control = udp_new();

   /* 2. Bind the upcb to the local port */
   ip_addr_t ip_addr;
   u16_t port = 7000;
   IP_ADDR4(&ip_addr, 10, 0, 64, 64);

   err_t err = udp_bind(udp_control, &ip_addr, port);

   /* 3. Set a receive callback for the upcb */
   if(err == ERR_OK) {
     udp_recv(udp_control, UDP_receive_handler, NULL);
   }
   else {
     udp_remove(udp_control);
   }
}

and then in the main function,

  /* USER CODE BEGIN 2 */

  UDP_init_server();
  
  /* USER CODE END 2 */

We can use a Python script to test it

import socket


ADDR = "10.0.64.64"
PORT = 7000

# open UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# send data
sock.sendto(b"Hello, world!", (ADDR, PORT))

print(f"Sent: Hello, world! to {ADDR}:{PORT}")

# receive data
data, addr = sock.recvfrom(1024)

print(f"Received: {data.decode()} from {addr}")

Client Logic

char buffer[128];
uint32_t counter = 0;
struct udp_pcb *upcb;

void udp_client_receive_callback(void *arg, struct udp_pcb *upcb, struct pbuf *p, const ip_addr_t *addr, u16_t port)
{
  /* Copy the data from the pbuf */
  strncpy (buffer, (char *)p->payload, p->len);

  /*increment message count */
  counter++;

  /* Free receive pbuf */
  pbuf_free(p);
}

void udpClient_connect(void)
{
  err_t err;

  /* 1. Create a new UDP control block  */
  upcb = udp_new();

  /* Bind the block to module's IP and port */
  ip_addr_t myIPaddr;
  IP_ADDR4(&myIPaddr, 10, 0, 64, 64);
  udp_bind(upcb, &myIPaddr, 8);


  /* configure destination IP address and port */
  ip_addr_t DestIPaddr;
  IP_ADDR4(&DestIPaddr, 10, 0, 0, 10);
  err= udp_connect(upcb, &DestIPaddr, 7000);

  if (err == ERR_OK)
  {
    /* 2. Send message to server */
    udpClient_send ();

    /* 3. Set a receive callback for the upcb */
    udp_recv(upcb, udp_client_receive_callback, NULL);
  }
}


void udpClient_send(void)
{
  struct pbuf *txBuf;
  char data[100];

  int len = sprintf(data, "sending UDP client message %d", counter);

  /* allocate pbuf from pool*/
  txBuf = pbuf_alloc(PBUF_TRANSPORT, len, PBUF_RAM);

  if (txBuf != NULL)
  {
    /* copy data to pbuf */
    pbuf_take(txBuf, data, len);

    /* send udp data */
    udp_send(upcb, txBuf);

    /* free pbuf */
    pbuf_free(txBuf);
  }
}





//  UDP_init_server();
  udpClient_connect();

  APP_init();
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
//    APP_main();
//    char str[128];
//    sprintf(str, "hello\n");
//    HAL_UART_Transmit(&huart3, (uint8_t *)str, strlen(str), 100);

    ethernetif_input(&gnetif);
    sys_check_timeouts();

    HAL_Delay(100);
    udpClient_send();
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }