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Exercise 1 – Pinging an echo server

In this exercise, we will learn how to set a UDP socket to ping an echo server and print its response on the terminal.

Exercise steps

In the GitHub repository for this course, go to the base code for this exercise, found in l3/l3_e1.

1. Set the necessary networking configurations

1.1 Configure the Zephyr networking API

Enable Zephyr native networking API through CONFIG_NETWORKING and the BSD socket-like API on top of Zephyr’s native networking API with CONFIG_NET_SOCKETS.

CONFIG_NETWORKING=y
CONFIG_NET_SOCKETS=y

Copy

CONFIG_NETWORKING=y
CONFIG_NET_SOCKETS=y

Kconfig

1.2 Enable the relevant networking configurations

Enable Ethernet support, CONFIG_NET_L2_ETHERNET, and IPv4 and IPv6 support for sending and receiving IP network packets.

We are using UDP as our transport layer protocol, so we also need to enable this.

CONFIG_NET_DHCPV4 enables the DHCPv4 client so the device can be assigned an IPv4 address from the DHCP server.

Enabling DNS resolver enables the device to resolve the address of the echo server using the hostname.

CONFIG_NET_L2_ETHERNET=y
CONFIG_NET_IPV4=y
CONFIG_NET_IPV6=y
CONFIG_NET_UDP=y
CONFIG_NET_DHCPV4=y
CONFIG_DNS_RESOLVER=y

Copy

CONFIG_NET_L2_ETHERNET=y
CONFIG_NET_IPV4=y
CONFIG_NET_IPV6=y
CONFIG_NET_UDP=y
CONFIG_NET_DHCPV4=y
CONFIG_DNS_RESOLVER=y

Kconfig

1.3 Configure network parameters.

Configure network parameters to optimize the networking stack performance and memory usage.

These values are often adjusted together as part of different usage profiles. The following settings are intended for moderate traffic scenarios. See Usage profiles for a list of network configurations for different profiles.

CONFIG_NET_TC_TX_COUNT=1
CONFIG_NET_BUF_TX_COUNT=16
CONFIG_NET_BUF_RX_COUNT=16
CONFIG_NET_PKT_TX_COUNT=8
CONFIG_NET_PKT_RX_COUNT=8
CONFIG_NET_TX_STACK_SIZE=4096
CONFIG_NET_RX_STACK_SIZE=4096

Copy

CONFIG_NET_TC_TX_COUNT=1
CONFIG_NET_BUF_TX_COUNT=16
CONFIG_NET_BUF_RX_COUNT=16
CONFIG_NET_PKT_TX_COUNT=8
CONFIG_NET_PKT_RX_COUNT=8
CONFIG_NET_TX_STACK_SIZE=4096
CONFIG_NET_RX_STACK_SIZE=4096

Kconfig

CONFIG_NET_TC_TX_COUNT – How many TX traffic classes to have for each network device
CONFIG_NET_BUF_TX_COUNT – How many network buffers are allocated for sending data
CONFIG_NET_BUF_RX_COUNT – How many network buffers are allocated for receiving data
CONFIG_NET_PKT_TX_COUNT – How many packet sends can be pending at the same time
CONFIG_NET_PKT_RX_COUNT – How many packet receives can be pending at the same time
CONFIG_NET_TX_STACK_SIZE – TX thread stack size
CONFIG_NET_RX_STACK_SIZE – RX thread stack size

2. Include the header file for the socket API.

#include <zephyr/net/socket.h>

Copy

#include <zephyr/net/socket.h>

3. Define the hostname and port for the echo server.

This is a UDP based echo server that we are running specifically for the Nordic Developer Academy courses.

#define SERVER_HOSTNAME "udp-echo.nordicsemi.academy"
#define SERVER_PORT "2444"

Copy

#define SERVER_HOSTNAME "udp-echo.nordicsemi.academy"
#define SERVER_PORT "2444"

4. Initialize variables for resolving the server address, creating the socket and receiving messages from the server.

4.1 Declare the structure for the socket used when creating the socket and the server address structure, used when connecting the socket.

static int sock;
static struct sockaddr_storage server;

Copy

static int sock;
static struct sockaddr_storage server;

Using struct sockaddr_storage instead of struct sockaddr is good practice as it promotes protocol-family independence (see here for a good explanation).

4.2 Declare the receive buffer for receiving messages from the UDP echo server.

static uint8_t recv_buf[MESSAGE_SIZE];

Copy

static uint8_t recv_buf[MESSAGE_SIZE];

5. Resolve the IP address of the server.

In the function server_resolve(), we will resolve the IP address of the server, retrieve the relevant information and print the address to console.

5.1 Call zsock_getaddrinfo() to get the IP address of the echo server.

Create the empty structure zsock_addrinfo result and the structure addrinfo hints and specify the family – IPv4 (AF_INET) and the socket type – UDP (SOCK_DGRAM) and then call zsock_getaddrinfo() with the hostname, and the other parameters to get the address.

int err;
struct zsock_addrinfo *result;
struct zsock_addrinfo hints = {
	.ai_family = AF_INET,
	.ai_socktype = SOCK_DGRAM
};
	
err = zsock_getaddrinfo(SERVER_HOSTNAME, SERVER_PORT, &hints, &result);
if (err != 0) {
	LOG_INF("getaddrinfo() failed, err: %d", err);
	return -EIO;
}

if (result == NULL) {
	LOG_INF("Error, address not found");
	return -ENOENT;
}

Copy

int err;
struct zsock_addrinfo *result;
struct zsock_addrinfo hints = {
	.ai_family = AF_INET,
	.ai_socktype = SOCK_DGRAM
};
	
err = zsock_getaddrinfo(SERVER_HOSTNAME, SERVER_PORT, &hints, &result);
if (err != 0) {
	LOG_INF("getaddrinfo() failed, err: %d", err);
	return -EIO;
}

if (result == NULL) {
	LOG_INF("Error, address not found");
	return -ENOENT;
}

5.2 Retrieve the relevant information from the result structure.

After zsock_getaddrinfo() is called, retrieve the relevant information from zsock_addrinfo result.

Create a pointer server4 of type struct sockaddr_in to point to server. Then set the address in server4 to point to the address from result. The family and port we already know, as AF_INET and SERVER_PORT.

struct sockaddr_in *server4 = ((struct sockaddr_in *)&server);
server4->sin_addr.s_addr = ((struct sockaddr_in *)result->ai_addr)->sin_addr.s_addr;
server4->sin_family = AF_INET;
server4->sin_port = ((struct sockaddr_in *)result->ai_addr)->sin_port;

Copy

struct sockaddr_in *server4 = ((struct sockaddr_in *)&server);
server4->sin_addr.s_addr = ((struct sockaddr_in *)result->ai_addr)->sin_addr.s_addr;
server4->sin_family = AF_INET;
server4->sin_port = ((struct sockaddr_in *)result->ai_addr)->sin_port;

5.3 Convert the address into a string and print it.

Convert the network address structure in server4->sin_addr.s_addr into a character string in ipv4_addr to print on the console.

char ipv4_addr[NET_IPV4_ADDR_LEN];
zsock_inet_ntop(AF_INET, &server4->sin_addr.s_addr, ipv4_addr, sizeof(ipv4_addr));
LOG_INF("IPv4 address of server found %s", ipv4_addr);

Copy

char ipv4_addr[NET_IPV4_ADDR_LEN];
zsock_inet_ntop(AF_INET, &server4->sin_addr.s_addr, ipv4_addr, sizeof(ipv4_addr));
LOG_INF("IPv4 address of server found %s", ipv4_addr);

5.4 Free the memory allocated for the zsock_addrinfo structure result, using zsock_freeaddrinfo().

zsock_freeaddrinfo(result);

Copy

zsock_freeaddrinfo(result);

6. Create a UDP socket.

In the function server_connect(), create an IPv4 UDP socket.

sock = zsock_socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (sock < 0) {
	LOG_INF("Failed to create socket: %d.\n", errno);
	return -errno;
}

Copy

sock = zsock_socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (sock < 0) {
	LOG_INF("Failed to create socket: %d.\n", errno);
	return -errno;
}

7. Connect the socket to the server.

Now let’s connect the socket we created to the echo server using the structure server.

err = zsock_connect(sock, (struct sockaddr *)&server, sizeof(struct sockaddr_in));
if (err < 0) {
	LOG_INF("Connect failed : %d\n", errno);
	return -errno;
}

Copy

err = zsock_connect(sock, (struct sockaddr *)&server, sizeof(struct sockaddr_in));
if (err < 0) {
	LOG_INF("Connect failed : %d\n", errno);
	return -errno;
}

8. Send a message every time button 1 is pressed.

In button_handler(), whenever button 1 is pressed call zsock_send() with the socket and message.

if (has_changed & DK_BTN1_MSK && button_state & DK_BTN1_MSK) {
	int err = zsock_send(sock, MESSAGE_TO_SEND, SSTRLEN(MESSAGE_TO_SEND), 0);
	if (err < 0) {
		LOG_INF("Failed to send message, %d", errno);
		return;
	} LOG_INF("Successfully sent message: %s", MESSAGE_TO_SEND);
}

Copy

if (has_changed & DK_BTN1_MSK && button_state & DK_BTN1_MSK) {
	int err = zsock_send(sock, MESSAGE_TO_SEND, SSTRLEN(MESSAGE_TO_SEND), 0);
	if (err < 0) {
		LOG_INF("Failed to send message, %d", errno);
		return;
	} LOG_INF("Successfully sent message: %s", MESSAGE_TO_SEND);
}

9. Resolve the server name and connect to the server.

In main(), call server_resolve() to resolve the IP address of the server, then call server_connect() to connect to it.

if (server_resolve() != 0) {
	LOG_INF("Failed to resolve server name");
	return 0;
}
	
if (server_connect() != 0) {
	LOG_INF("Failed to connect to server");
	return 0;
}

Copy

if (server_resolve() != 0) {
	LOG_INF("Failed to resolve server name");
	return 0;
}
	
if (server_connect() != 0) {
	LOG_INF("Failed to connect to server");
	return 0;
}

10. Listen for incoming messages.

In the while-loop in main, call zsock_recv() to listen to received messages.

If zsock_recv() returns with a positive integer, then the string is null-terminated and we print the received message.

received = zsock_recv(sock, recv_buf, sizeof(recv_buf) - 1, 0);

if (received < 0) {
	LOG_ERR("Socket error: %d, exit", errno);
	break;
}

if (received == 0) {
	LOG_ERR("Empty datagram");
	break;
}

recv_buf[received] = 0;
LOG_INF("Data received from the server: (%s)", recv_buf);

Copy

received = zsock_recv(sock, recv_buf, sizeof(recv_buf) - 1, 0);

if (received < 0) {
	LOG_ERR("Socket error: %d, exit", errno);
	break;
}

if (received == 0) {
	LOG_ERR("Empty datagram");
	break;
}

recv_buf[received] = 0;
LOG_INF("Data received from the server: (%s)", recv_buf);

11. Build and flash the application to your board.

This exercise uses the PSA backend for storing the Wi-Fi credentials. Therefore, you must build with TF-M.

Board	Build with TF-M	Extra CMake arguments
nRF7002 DK	`nrf7002dk/nrf5340/cpuapp/ns`	N/A
nRF5340 DK + nRF7002 EK	`nrf5340dk/nrf5340/cpuapp/ns`	`-DSHIELD=nrf7002ek`

12. Connect to a Wi-Fi network.

Connect to your Wi-Fi network by running the below commands in the terminal

Note that if the Wi-Fi credentials are still stored on the device from the previous exercise, the connection will happen automatically.

wifi cred add -s "<your_network_SSID>" -p "<your_network_password>" -k <key_mgmt>
wifi cred auto_connect

Copy

wifi cred add -s "<your_network_SSID>" -p "<your_network_password>" -k <key_mgmt>
wifi cred auto_connect

Recall

You can run wifi scan to find the key management type of the network you want to connect to and wifi cred add help for a list of the corresponding numbers.

If the connection was successful, you should see the following log output

*** Booting nRF Connect SDK ***
*** Using Zephyr OS ***
[00:00:00.566,162] <inf> wifi_supplicant: wpa_supplicant initialized
[00:00:12.174,896] <inf> wifi_mgmt_ext: Connection requested
[00:00:12.175,567] <inf> Lesson3_Exercise1: Waiting to connect to Wi-Fi
Connected
[00:00:16.518,096] <inf> Lesson3_Exercise1: Network connected
[00:00:16.553,039] <inf> Lesson3_Exercise1: IPv4 address of server found 20.82.16.164
[00:00:16.553,527] <inf> Lesson3_Exercise1: Successfully connected to server
[00:00:16.553,558] <inf> Lesson3_Exercise1: Press button 1 on your DK to send your message

Terminal

13. Press button 1 on the board a couple times and observe the following output.

[00:00:27.078,582] <inf> Lesson3_Exercise1: Successfully sent message: Hello from nRF70 Series
[00:00:27.124,542] <inf> Lesson3_Exercise1: Data received from the server: (Time: 2023-11-07 21:32:17 Message: Hello from nRF70 Series)
[00:00:36.707,458] <inf> Lesson3_Exercise1: Successfully sent message: Hello from nRF70 Series
[00:00:36.742,706] <inf> Lesson3_Exercise1: Data received from the server: (Time: 2023-11-07 21:32:26 Message: Hello from nRF70 Series)
[00:00:43.133,178] <inf> Lesson3_Exercise1: Successfully sent message: Hello from nRF70 Series
[00:00:43.174,926] <inf> Lesson3_Exercise1: Data received from the server: (Time: 2023-11-07 21:32:33 Message: Hello from nRF70 Series)

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Wi-Fi Fundamentals

Exercise 1 – Pinging an echo server

Exercise steps

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