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products:sbc:common:applications:gpio:uart

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products:sbc:common:applications:gpio:uart [2022/06/29 21:51]
127.0.0.1 external edit 		products:sbc:common:applications:gpio:uart [2024/08/06 08:27] (current)
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-# UART+===== UART ===== 
 + 
 +===== Introduction ===== 
 + 
 +This page introduces the usage of UART on [[products:sbc:common:applications:gpio:40pin-header|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 [[products:sbc:common:configurations:device-tree-overlay|Device Tree Overlay]]. 
 + 
 +<tabbox 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. 
 + 
 +```shell 
 +overlays=pwm_ao_a pwm_f uart3 
 +``` 
 + 
 +After reboot, you will see the UART device node. 
 + 
 +```shell 
 +$ ls /dev/ttyS3 
 +/dev/ttyS3 
 +``` 
 + 
 +<tabbox 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. 
 + 
 +```shell 
 +fdt_overlays=uart3 
 + 
 +``` 
 + 
 +After reboot, you will see the UART device node. 
 + 
 +```shell 
 +$ ls /dev/ttyS3 
 +/dev/ttyS3 
 +``` 
 + 
 +<tabbox 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. 
 + 
 +```shell 
 +fdt_overlays=uart3 
 + 
 +``` 
 + 
 +After reboot, you will see the UART device node. 
 + 
 +```shell 
 +$ ls /dev/ttyS3 
 +/dev/ttyS3 
 +``` 
 + 
 +<tabbox 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. 
 + 
 +```shell 
 +fdt_overlays=uart_e 
 + 
 +``` 
 + 
 +After reboot, you will see the UART device node. 
 + 
 +```shell 
 +$ ls /dev/ttyS4 
 +/dev/ttyS4 
 +``` 
 + 
 +<tabbox 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. 
 + 
 +```shell 
 +fdt_overlays=uart_c 
 + 
 +``` 
 + 
 +After reboot, you will see the UART device node. 
 + 
 +```shell 
 +$ ls /dev/ttyS2 
 +/dev/ttyS2 
 +``` 
 + 
 +</tabbox> 
 + 
 + 
 +==== Android ==== 
 + 
 +<tabbox VIM1S> 
 + 
 +''UART_C'' is enabled by default in ''kvim1s.dts'', The corresponding device node is ''/dev/ttyS2''. 
 + 
 + 
 +<tabbox VIM4> 
 + 
 +''UART_E'' is enabled by default, the corresponding dev node is ''/dev/ttyS4''. 
 + 
 +<tabbox VIM3> 
 + 
 +''UART_C'' is enabled by default in ''kvim3.dts'', The corresponding device node is ''/dev/ttyS3''. 
 + 
 +</tabbox> 
 + 
 +===== 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 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 [[products:sbc:common:configurations:device-tree-overlay|Device Tree Overlay]]. 
Last modified: 2022/06/29 21:51 by 127.0.0.1

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