> For the complete documentation index, see [llms.txt](https://tk233.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://tk233.gitbook.io/notes/stm32/connectivity/ethernet/ethernet-udp.md).

# Ethernet - UDP

Set up LWIP according to the previous note

{% embed url="<https://controllerstech.com/stm32-ethenret-2-udp-server/>" %}

```c

#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,&#x20;

```c
  /* USER CODE BEGIN 2 */

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

We can use a Python script to test it

```python
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

```c

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 */
  }
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://tk233.gitbook.io/notes/stm32/connectivity/ethernet/ethernet-udp.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.