This it the third tutorial in the STM32 Ethernet series, and today we will see how to create UDP client using STM32. I have already covered a tutorial about UDP SERVER, you can check it out here.

The hardware connection will be similar to the one I have used in the first video, and you can check it out here.

Some Insight into the CODE

Connect the Client to the server

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, 192, 168, 0, 111);
	udp_bind(upcb, &myIPaddr, 8);

	/* configure destination IP address and port */
	ip_addr_t DestIPaddr;
	IP_ADDR4(&DestIPaddr, 192, 168, 0, 102);
	err= udp_connect(upcb, &DestIPaddr, 7);

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

		/* 3. Set a receive callback for the upcb */
		udp_recv(upcb, udp_receive_callback, NULL);
  • We are going to use the following steps to connect the UDP client to a server
  • First of all we will create a new UDP control block, using udp_new ()
  • Next I am binding the control block to the local IP and port, using udp_bind ()
  • Also connect the control block to the server IP and port, using udp_connect()
  • Then we will send some data to the server, and set a receive function, which will be called, when the server sends some data to the client.

The Receive callback

void udp_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 */

	/* Free receive pbuf */

The receive callback is called, when the client receives some data from the server. Let’s see ho am I handling this function

  • here I am copying the data sent by the server into the buffer.
  • Although I am not making any use of this data, but you can utilize it as per your requirement.
  • then increment the counter. This counter will be used when we will send the data.
  • Finally free the packet buffer.

Sending Data to the Server

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)

static 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 */
  • Here I have also created a periodic timer, which will generate an interrupt every 1 second.
  • The data will be sent to the server in the timer callback, and hence every 1 second.
  • To send the data to the server, first of all we will create a packet buffer, txBuf
  • Then we will allocate the memory for this packet buffer
  • pbuf_take will be used to copy the data into the packet buffer.
  • And finally we will send the data using the udp_send function.


Check out the VIDEO Below


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