This page introduces the usage of hardware UART on 16-pin Header.

In order to use the UART, you need to enable the UART function via Device Tree Overlay.

Edit /boot/dtb/rockchip/rk3588s-khadas-edge2.dtb.overlay.env to add uart node to fdt_overlays node if it doesn't exist.

e.g. Enable UART7, you need to add edge2-io-uart to node fdt_overlays if it doesn't exist.

fdt_overlays=edge2-io-uart

After reboot, you will see the UART device node.

$ ls /dev/ttyS7
/dev/ttyS7

uart.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
 
// set serial path
#define SERIAL_PORT "/dev/ttyS7"
 
int main() {
    int serial_port;
    struct termios tty;
 
    // open
    serial_port = open(SERIAL_PORT, O_RDWR | O_NOCTTY);
    if (serial_port < 0) {
        perror("Error opening serial port");
        return 1;
    }
 
    // Configuration of serial
    memset(&tty, 0, sizeof(tty));
    if (tcgetattr(serial_port, &tty) != 0) {
        perror("Error getting serial port attributes");
        close(serial_port);
        return 1;
    }
 
    cfsetospeed(&tty, B1500000); // set baud rate
    cfsetispeed(&tty, B1500000);
 
    tty.c_cflag |= (CLOCAL | CREAD);
    tty.c_cflag &= ~PARENB;     
    tty.c_cflag &= ~CSTOPB;     
    tty.c_cflag &= ~CSIZE;
    tty.c_cflag |= CS8;         
 
    // write configration to serial
    if (tcsetattr(serial_port, TCSANOW, &tty) != 0) {
        perror("Error setting serial port attributes");
        close(serial_port);
        return 1;
    }
 
    // loop test
    while (1) {
        // receive data
        char received_data[64];
        if (read(serial_port, &received_data, sizeof(char)*64)) {
            // get data
            printf("Received: %s", received_data);
        }
 
        // Only send "Hello, UART!"
        char data_to_send[] = "Hello, UART!\n";
        write(serial_port, data_to_send, strlen(data_to_send));
 
        // sleep 100ms
        usleep(100000); 
    }
 
    // close
    close(serial_port);
 
    return 0;
}

Compile test code:

$ gcc uart.c -o uart

Run uart

$ ./uart

After connecting PIN12(STX), PIN14(CSO) and GND to PC, open ttyUSBX and input hello

1 hello
2 Hello, UART!

Check output data:

$ ./uart
Received: hello

If you want to use normal GPIO instead of UART, you can remove the UART node in Device Tree Overlay.