[Raspberry] 在Raspberry Pi 2 使用 UART

確認Pi 沒有主控台控制權,如果有,先關閉

pi@raspberrypi:~ $ dmesg | grep tty

[    0.000000] Kernel command line: dma.dmachans=0x7f35 bcm2708_fb.fbwidth=1024 bcm2708_fb.fbheight=768 bcm2709.boardrev=0xa21041 bcm2709.serial=0xf1ba6d8 smsc95xx.macaddr=B8:27:EB:1B:A6:D8 bcm2708_fb.fbswap=1 bcm2709.uart_clock=48000000 bcm2709.disk_led_gpio=47 bcm2709.disk_led_active_low=0 vc_mem.mem_base=0x3dc00000 vc_mem.mem_size=0x3f000000  dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait

[    0.001532] console [tty1] enabled

[    0.093340] 3f201000.uart: ttyAMA0 at MMIO 0x3f201000 (irq = 87, base_baud = 0) is a PL011 rev2

[    0.596998] console [ttyAMA0] enabled

[    4.446432] systemd[1]: Expecting device dev-ttyAMA0.device...

[    5.297264] systemd[1]: Starting system-serial\x2dgetty.slice.

[    5.319043] systemd[1]: Created slice system-serial\x2dgetty.slice.

pi@raspberrypi:~ $

關閉方式:

Sudo raspi-config

選 9 Advanced Options

選 A7 Serial  Enable/Disable shell and kernel messages on the serial connection ,關閉他 

Reboot後, dmesg | grep tty

pi@raspberrypi:~ $ dmesg | grep tty

[    0.000000] Kernel command line: dma.dmachans=0x7f35 bcm2708_fb.fbwidth=1024 bcm2708_fb.fbheight=768 bcm2709.boardrev=0xa21041 bcm2709.serial=0xf1ba6d8 smsc95xx.macaddr=B8:27:EB:1B:A6:D8 bcm2708_fb.fbswap=1 bcm2709.uart_clock=48000000 bcm2709.disk_led_gpio=47 bcm2709.disk_led_active_low=0 vc_mem.mem_base=0x3dc00000 vc_mem.mem_size=0x3f000000  dwc_otg.lpm_enable=0 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait

[    0.001516] console [tty1] enabled

pi@raspberrypi:~ $

關閉了

去查看 /dev/ttyAMA0 不見了(網路上的範例都是用這個PORT勒 !!!)

參考資料,第一二篇有寫了一大推解決方法……..太難了,看無

進入視窗,左上角 Menu -> Preferences -> Raspberry Pi Configuration ->Interfaces -> Serial --> Enable

Sudo apt-get install minicom  安裝軟體

sudo minicom –b 9600 –o –D /dev/ttyAMA0

切換至新視窗後,按鍵盤的Key,確認在示波器有看到輸出信號

gpio readall -- >check state of all pin

gpio mode 15 ALTO -->第8pin改成 ALTO state

程式:

Sudo chmod a+rw /dev/ttyAMA0  -->如果沒權限,就無法open port

#include <cstdlib>

#include <stdio.h>

#include <unistd.h>

#include <fcntl.h>

#include <termios.h>

using namespace std;

int main(int argc, char** argv) {

    //setup UART

    int uart_filestream=-1;

    uart_filestream=open("/dev/ttyAMA0",O_RDWR | O_NOCTTY | O_NDELAY);

    if(uart_filestream==-1)

    {

        printf("Unable to Open UART \r\n ");

        return 0;

    }

   

    //Configure UART

    struct termios options;

    tcgetattr(uart_filestream,&options);

    options.c_cflag=B9600 | CS8 | CLOCAL | CREAD;

    options.c_iflag=IGNPAR;

    options.c_oflag=0;

    options.c_lflag=0;

    tcflush(uart_filestream,TCIFLUSH);

    tcsetattr(uart_filestream,TCSANOW,&options);

   

    //Transmitting

    unsigned char tx_buf[10];

    unsigned char *p_buffer;  

    p_buffer=&tx_buf[0];

    *p_buffer++='O';

    *p_buffer++='I';

    *p_buffer++='A';

    if(uart_filestream !=-1)

    {

        int count=write(uart_filestream,&tx_buf[0],(p_buffer-&tx_buf[0]));

        if(count<0)

            printf("TX error \r\n");

    }

    

    close(uart_filestream);

    printf("finish\r\n");

    return 0;

}

參考資料:

Raspberry Raspbian turning off the UART functioning as a serial console

http://m.blog.csdn.net/article/details?id=51817505

Why my program won't communicate through ttyAMA0 on Raspbian (Jessie)?

http://raspberrypi.stackexchange.com/questions/47671/why-my-program-wont-communicate-through-ttyama0-on-raspbian-jessie

Serial(UART) communication on Raspberry Pi 2

http://scaluza.com/raspberry-pi/serial-uart-communication-on-raspberry-pi-2/#.V9J-2vl962x

Raspberry Pi 釋放主控台序列埠(GPIO14,GPIO15)

http://yehnan.blogspot.tw/2015/03/raspberry-pigpio14gpio15.html

Using the UART (C語言)

http://www.raspberry-projects.com/pi/programming-in-c/uart-serial-port/using-the-uart