Table of Contents

VIM2 UART

Introduction

This page introduces the usage of UART on 40pin-Header.

UART Information

UART PIN GPIO Name DT Overlays Node Device Node
VIM1/2 UART_AO_B 15(RX) GPIOAO_5 uart4 /dev/ttyS4
16(TX) GPIOAO_4
VIM3/3L UART_C 15(RX) GPIOH_6 uart3 /dev/ttyS3
16(TX) GPIOH_7
VIM4 UART_E 15(RX) GPIOY_7 uart_e /dev/ttyS4
16(TX) GPIOY_6
VIM1S UART_C 15(RX) GPIOD_3 uart_c /dev/ttyS2
16(TX) GPIOD_2

Enable UART

Linux

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

VIM1/2/3/3L/Edge1

Edit /boot/env.txt to add the uart node to overlays node if it doesn't exist.

Take VIM3 as an example to enable UART_C, you need to add uart3 node to overlays node if it doesn't exist. 

overlays=pwm_ao_a pwm_f uart3

After reboot, you will see the UART device node. 

$ ls /dev/ttyS3
/dev/ttyS3

VIM3 with 5.15 kernel

Edit /boot/dtb/amlogic/kvim3.dtb.overlay.env to add uart node to fdt_overlays node if it doesn't exist.

e.g. Enable UART_C, you need to add uart3 to node fdt_overlays if it doesn't exist. 

fdt_overlays=uart3

After reboot, you will see the UART device node. 

$ ls /dev/ttyS3
/dev/ttyS3

VIM3L with 5.15 kernel

Edit /boot/dtb/amlogic/kvim3l.dtb.overlay.env to add uart node to fdt_overlays node if it doesn't exist.

e.g. Enable UART_C, you need to add uart3 to node fdt_overlays if it doesn't exist. 

fdt_overlays=uart3

After reboot, you will see the UART device node. 

$ ls /dev/ttyS3
/dev/ttyS3

VIM4

Edit /boot/dtb/amlogic/kvim4.dtb.overlay.env to add uart node to fdt_overlays node if it doesn't exist.

e.g. Enable UART_E, you need to add uart_e to node fdt_overlays if it doesn't exist. 

fdt_overlays=uart_e

After reboot, you will see the UART device node. 

$ ls /dev/ttyS4
/dev/ttyS4

VIM1S

Edit /boot/dtb/amlogic/kvim1s.dtb.overlay.env to add uart node to fdt_overlays node if it doesn't exist.

e.g. Enable UART_C, you need to add uart_c to node fdt_overlays if it doesn't exist. 

fdt_overlays=uart_c

After reboot, you will see the UART device node. 

$ ls /dev/ttyS2
/dev/ttyS2

Android

VIM1S

UART_C is enabled by default in kvim1s.dts, The corresponding device node is /dev/ttyS2.

VIM4

UART_E is enabled by default, the corresponding dev node is /dev/ttyS4.

VIM3

UART_C is enabled by default in kvim3.dts, The corresponding device node is /dev/ttyS3.

Demo Source Code

uart.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <termios.h>
 
// set correct serial path
#define SERIAL_PORT "/dev/ttyS2"
 
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, B921600); // set correct baud rate
    cfsetispeed(&tty, B921600);
 
    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

Test demonstration

Run uart 

$ ./uart

After connecting PIN15, PIN16 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 Device Tree Overlay.

2022/06/29 09:38 · 1 Comment