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  Linux based serial programming
     
  Add Date : 2018-11-21      
         
         
         
  Linux Serial programming, the configuration process is like stop bits, parity, baud rate and data bits. Open the file as open as serial devices, then configure the above said several parameters. Write serial port using a standard Linux system calls write, read with read. Of which there are some configuration in the code in detail, directly attached to the following Code:

Serial.cfg first with a configuration file to specify the parameters of the serial port, directly behind the changes to the configuration file to modify parameters. We call this configuration file in / etc / below

DEV = / dev / tq2440_serial2
SPEED = 115200
DATABITS = 8
STOPBITS = 1
PARITY = N

Here's some serial device file has been used to generate drive device nodes.

Definitions header file Serial.h, characterize the structure define the serial port

#ifndef SERIAL_PORT_H
#define SERIAL_PORT_H

#define TRUE 1
#define FALSE 0

#define z_U32 unsigned int
#define z_U8 unsigned char

#define SERIAL_NAME_LEN 32
extern int serial_config ();
extern int set_speed (int fd);
extern int set_other_parm (int fd);

typedef struct z_Serial_port {

 z_U8 serial_name [SERIAL_NAME_LEN];
 z_U32 serial_baud;
 z_U8 data_bits;
 z_U8 stop_bits;
 z_U8 parity;

} HI_Serial_port;

extern z_Serial_port get_current_serial ();
#endif

The next course is slightly serial.c file, set the serial port to achieve the various parameters

/ *
** Author: z
** CopyRight: z
** Funtion: serial port Interface
** Date: 2014
* /

#include / ** /
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include "pthread.h"

#include "serial_port.h"

#define CFG_FILE "/etc/serial.cfg"// place where profile
#define DEBUG 1
#define ERROR -1
#define OK 1

/ * Serial Port Struct * /
z_Serial_port serial_port;

int speed_array [] = {B230400, B115200, B57600, B38400, B19200, B9600, B4800,
                    B2400, B1200, B300, B38400, B19200, B9600, B4800,
                    B2400, B1200, B300};
int name_array [] = {230400, 115200, 57600, 38400, 19200, 9600, 4800,
                    2400, 1200, 300, 38400, 19200, 9600, 4800,
                    2400, 1200, 300};

// Get the current serial structure

z_Serial_port get_current_serial () {
 z_Serial_port current_serial;
 memset (current_serial.serial_name, 0, sizeof (current_serial.serial_name));

  strncpy (current_serial.serial_name, serial_port.serial_name, sizeof (current_serial.serial_name));
  current_serial.serial_baud = serial_port.serial_baud;
  current_serial.data_bits = serial_port.data_bits;
  current_serial.stop_bits = serial_port.stop_bits;
  current_serial.parity = serial_port.parity;
  if (DEBUG) {
   printf ( "current_serial.serial_baud =% d n", current_serial.serial_baud);
   printf ( "current_serial.data_bits =% d n", current_serial.data_bits);
   printf ( "current_serial.stop_bits =% d n", current_serial.stop_bits);
   printf ( "current_serial.parity =% c n", current_serial.parity);
  }
  return current_serial;
}

// Read the serial port profile, and configure filled structure

int serial_config ()
{
    FILE * serial_fp;
    char read_buf [20] = {0};
    char temp [20];
    char parity;

    / * Read serial config from file * /
    serial_fp = fopen (CFG_FILE, "r");
    if (serial_fp == NULL) {
        printf ( "Can not open serial config file n");
        return ERROR;
    }
    memset (serial_port.serial_name, 0, sizeof (serial_port.serial_name));
    fscanf (serial_fp, "DEV =% s n", serial_port.serial_name);
    
    fscanf (serial_fp, "SPEED =% s n", temp);
    serial_port.serial_baud = atoi (temp);

    fscanf (serial_fp, "DATABITS =% s n", temp);
    serial_port.data_bits = atoi (temp);

    fscanf (serial_fp, "STOPBITS =% s n", temp);
    serial_port.stop_bits = atoi (temp);

    fscanf (serial_fp, "PARITY =% s n", temp);
    serial_port.parity = temp [0];

    if (DEBUG) {
        printf ( "Serial Dev =% s n", serial_port.serial_name);
        printf ( "Serial Speed ​​=% d n", serial_port.serial_baud);
        printf ( "Serial DataBits =% d n", serial_port.data_bits);
        printf ( "Serial StopBite =% d n", serial_port.stop_bits);
        printf ( "Serial Parity =% c n", serial_port.parity);
    }
    fclose (serial_fp);
    return OK;
}

/ *
 * Set Baudrate
 * Set the baud rate, fd is open handle to the device node
 * * /
int set_speed (int fd)
{
    struct termios option;
    struct termios old_option;
    int i = 0;

    // Get the old option
    tcgetattr (fd, & old_option); // termios structure is to be operated

    for (i = 0; i         if (serial_port.serial_baud == name_array [i]) {
    tcflush (fd, TCIOFLUSH);
        cfsetispeed (& option, speed_array [i]);
        cfsetospeed (& option, speed_array [i]);

    if (tcsetattr (fd, TCSANOW, & option)! = 0) {// configuration takes effect immediately
  printf ( "set serial baudrate failed n");
  return ERROR;
    } Else {
  tcflush (fd, TCIOFLUSH); // clear the input and output queues
        if (DEBUG) printf ( "set serial baudrate sucessed n");
  return OK;
    }
 }
    }
}

/ *
 * Set Other Paramters
 * Set the other parameters
 * * /
int set_other_parm (int fd)
{
    struct termios options;
    struct termios old_options;

    if (tcgetattr (fd, & old_options)! = 0) {
 printf ( "Failed to getattr n");
 return ERROR;
    }
    options.c_cflag | = (CLOCAL | CREAD);
    options.c_cflag & = ~ CSIZE;

    / * Set Date Bits * /
    switch (serial_port.data_bits) {
        case 7:
    options.c_cflag | = CS7;
    break;
 case 8:
    options.c_cflag | = CS8;
    break;
 default:
    options.c_cflag | = CS8;
        break;
    }

    / * Set Parity Bites * /
    switch (serial_port.parity) {
 case 'n':
 case 'N':
    options.c_cflag & = ~ PARENB;
    options.c_iflag & = ~ INPCK;
    break;
 case 'o':
 case 'O':
    options.c_cflag | = (PARODD | PARENB);
    options.c_iflag | = INPCK;
    break;
 case 'e':
 case 'E':
    options.c_cflag | = PARENB;
    options.c_cflag & = ~ PARODD;
    options.c_iflag | = INPCK;
    break;
 default:
    options.c_cflag & = ~ PARENB;
    options.c_iflag & = ~ INPCK;
        break;
    printf ( "default parity none parity n");
    }

    / * Set Stop Bites * /
    switch (serial_port.stop_bits) {
 case 1:
    options.c_cflag & = ~ CSTOPB;
    break;
 case 2:
    options.c_cflag | = CSTOPB;
    break;
 default:
    options.c_cflag & = ~ CSTOPB;
    }
    if (serial_port.parity! = 'n' || serial_port.parity! = 'N') {
 options.c_iflag | = INPCK;
    }
    options.c_cc [VTIME] = 0; // set timeout Timeout parma
    options.c_cc [VMIN] = 0; // read x bite return the number of bytes read before the operation, here is set to 0

 options.c_iflag | = IGNPAR | ICRNL;
    options.c_oflag | = OPOST; // original mode, there are two modes, if it is the original model, then this will be n only after output
    options.c_iflag & = ~ (IXON | IXOFF | IXANY);


    tcflush (fd, TCIFLUSH);
    if (tcsetattr (fd, TCSANOW, & options)! = 0) {
 printf ( "set serial other parma failed n");
 return ERROR;
    }
    return OK;
}

Here, the basic parameters on the configuration finished, to note here configurations and configuration VMIN and VTIME original model.

Interface written, write a test program to test like the test program write more ugly, forgive me, ha ha:

#include
#include
#include
#include

#include "serial_port.h"

int main (int argc, char * argv [])
{
 int ret;
 int fd;
 unsigned char data [50];

    z_Serial_port serial_p;

 printf ( "Configing serial from local file ... n");
 ret = serial_config ();
 if (ret! = 1) {
  printf ( "Failed to config serial n");
  return -1;
 }
 serial_p = get_current_serial ();
 fd = open (serial_p.serial_name, O_RDWR, 0); // open the way to read and write
 printf ( "opening% s n..", serial_p.serial_name);
 if (fd == -1) {
  printf ( "Can not open tty n");
  return -1;
 }
 // Set speed
    if (set_speed (fd) <0) {
  printf ( "set speed Failed n");
  return -1;
 }
 if (fcntl (fd, F_SETFL, O_NONBLOCK) <0) {
  printf ( "fcntl failed n");
  return -1;
 }
    if (isatty (STDIN_FILENO) == 0)
    {
        printf ( "not a terminal device n");
    } Else
        printf ( "! isatty success n");
 // Set other parma like stopbites etc.
    if (set_other_parm (fd) <0) {
  printf ( "set other parm failed n");
  return -1;
 }
 // Write data
 int i;
    char buff [512];
    char buff21 [] = "Hi Babby!";

    int nread, nwrite = 0;
    int nx;
    printf ( "fd =% d n", fd);
    nx = write (fd, buff21, sizeof (buff21));


    printf ( "nx =% d n", nx);
    while (1)
    {
        if ((nread = read (fd, buff, 512))> 0)
        {
            buff [nread] = ' 0';
            // Write (fd, buff, nread);
            printf ( " nrecv:% d n", nread);
            // Printf ( "% s", buff);
   printf ( "% d", buff [0]);
   printf ( "% d", buff [1]);
   printf ( "% d", buff [2]);
   printf ( "% d", buff [3]);
            printf ( " n");
        }
 
    }
 return 1;
}

He put MakeFile

CC = arm-linux-gcc
SEND_EXEC = serial_send

all: serial_port.c serial_port.h serial_send_msg.c
 $ (CC) -o $ (SEND_EXEC) serial_port.c serial_send_msg.c
#chmod 777 $ (SEND_EXEC)
clean:
 rm -rf * .o serial_send

Haha, is completed, the next step is testing. Here the circuit board TXD2 and RXD2 short, that spontaneous self-reading, serial print "Hi Babby!" Hey, get. Back will play out a GSM module. Also serial

Send AT commands to communicate. To pass the time during the relevant transfer analysis.
     
         
         
         
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