~~tag>Edge2 UART~~

====== Edge2 UART ======



===== Introduction =====

This page introduces the usage of hardware UART on [[products:sbc:edge2:applications:gpio:40pin-header|16-pin Header]].

<WRAP important >
For Edge2, in order to use the UART , you need to attach the IO extension board.
</WRAP>
===== UART Information =====

|           ^  UART       ^ PIN      ^ GPIO Name  ^ GPIO Number  ^  DT Overlays Node  ^  Device Node  ^
^  Edge2    |  UART7      |  12(TX)  |  GPIO3_C0  |  112         |  edge2-io-uart     |  /dev/ttyS7   |   
| :::       | :::         |  14(RX)  |  GPIO3_C1  |  113         | :::                | :::           |
===== Enable UART =====

In order to use the UART, you need to enable the UART function via [[products:sbc:common:configurations:device-tree-overlay|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.

```shell
fdt_overlays=edge2-io-uart
```
After reboot, you will see the UART device node. 

```shell
$ ls /dev/ttyS7
/dev/ttyS7
```

===== Demo Source Code =====
```c 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
```

===== Disable UART to Use GPIO =====

If you want to use normal GPIO instead of UART, you can remove the UART node in [[products:sbc:common:configurations:device-tree-overlay|Device Tree Overlay]].