Linux环境下使用interrupt方式操作UART

概述

1 Linux环境下UART设备

2 轮询方式操作UART功能实现

2.1 打开串口函数：usr_serial_open

2.2 关闭串口函数： usr_serial_close

2.3 发送数据函数： usr_serial_sendbytes

2.4 接收数据函数： usr_serial_readinterrupt

3 完整代码

3.1 usr_serial.c 文件内容

3.1 usr_serial.h 文件内容

4 编写测试代码

4.1 编写测试代码

4.2 编写测试代码的Makefile

5 测试中断模式下串口数据的发送和接收功能

源代码下载地址：Linux环境下使用interrupt方式操作UART资源-CSDN文库

概述

本文介绍Linux环境下使用interrupt方式操作UART的方法，实现了串口打开，关闭，发送数据，接收数据功能，还编写测试代码，验证该功能。

1 Linux环境下UART设备

在linux环境下,UART作为一个终端设备存在，可使用命令，系统会罗列出该目录下所有的device,其中以tty开头的设备为终端设备。串口也是这些设备之一。

ls /dev/ -l

执行该命令后，可以看见许多以tty开头的设备：

user根据板卡的信息，找到对应的端口，然后才能使用这些串口，笔者使用是基于iMX6ull芯片的板卡，板卡上COM1被用于调试终端，COM3可作为用户终端。

2 轮询方式操作UART功能实现

2.1 打开串口函数：usr_serial_open

函数参数

参数	描述
port	终端设备: /dev/tty0
baudrate	波特率： 1200/2400/4800 ... /115200
databit	数据bit位： /5/6/7/8
stopbit	停止位："1" / "1.5" / "2"
parity	奇偶位使能： 'N' / 'E' / 'O'

函数实现方法：

代码 43行：打开端口

代码 49行：保存termios数据结构中，旧的参数

代码 51行：设置当前用户参数

源代码：

int usr_serial_open( char *port, unsigned int baudrate, 
                     unsigned int databit, const char *stopbit, char parity)
{
    int err;
    
    fd = open (port, O_RDWR | O_NOCTTY | O_NDELAY);
    if (-1 == fd) {
        fprintf(stderr, "cannot open port %s\n", port);
        return (-1);
    }
    
    tcgetattr (fd, &termios_old);       /* save the form termios value */
      
    err = set_portattr (baudrate, databit, stopbit, parity);
    if ( err ) {
        fprintf ( stderr, "\nport %s cannot set baudrate at %d\n",
                  port, baudrate);
    }
    usr_baudrate = baudrate;
    
    return fd;
}

2.2 关闭串口函数： usr_serial_close

函数实现方法：

代码 64行：恢复termios default参数

代码 65行：关闭fd端口

void usr_serial_close( void )
{
    /* flush output data before close and restore old attribute */
    tcsetattr(fd, TCSADRAIN, &termios_old);
    close(fd);
}

2.3 发送数据函数： usr_serial_sendbytes

函数参数

参数	描述
*data	存贮数据的数组
datalength	发送的数据长度

函数实现方法：

代码 72行：使用write函数发送数据

2.4 接收数据函数： usr_serial_readinterrupt

函数参数

参数	描述
*data	存贮数据的数组
datalength	接收的数据长度

函数实现方法：

代码 100~102行：配置接收中断

代码 104行：使用read函数写数据

unsigned int usr_serial_readinterrupt (void *data, unsigned int datalength)
{
    int total_len = 0;

    /**
     * caculate the time of 5 characters and get the maxim
     * with 3ms and 5 ch's time
    */
    tv_timeout.tv_sec = 0;
    tv_timeout.tv_usec = ( (CH_TO_WAIT * CH_BITS) * (1000000/usr_baudrate));

    while(1){
        FD_ZERO (&fs_read);
        FD_SET (fd, &fs_read);
        select (fd + 1, &fs_read, NULL, NULL, &tv_timeout);
        
        total_len = read(fd, data, datalength);
        if (total_len > 0) {
            printf("Receive %d bytes: %.*s\n", total_len, (char*)data);
            return total_len;
        }
    }

    return total_len;

}

3 完整代码

代码文件命名为usr_serial，包含两个文件

usr_serial.c
usr_serial.h

3.1 usr_serial.c 文件内容

/***************************************************************
Copyright  2024-2029. All rights reserved.
文件名     : 01_usr_serial.c
作者       : tangmingfei2013@126.com
版本       : V1.0
描述       : linux 串口应用程序接口
其他       : 无
日志       : 初版V1.0 2024/03/01

***************************************************************/
#include "usr_serial.h"

/* Private define ------------------------------------------------------------*/
#define TIMEOUT_SEC(buflen,baud)    (buflen*20/baud+2)
#define TIMEOUT_USEC                 0

#define CH_TO_WAIT 5
#define CH_BITS 11

/* Private variables ---------------------------------------------------------*/
static unsigned int fd;  

static struct timeval tv_timeout;
static struct termios termios_old;
static struct termios termios_new;

static fd_set fs_read;
static unsigned int usr_baudrate;



/* Private function prototypes -----------------------------------------------*/
static speed_t baudrate_to_Bxx (unsigned int baudrate);
static void set_data_bit (unsigned int databit);
static unsigned int set_portattr ( unsigned int baudrate,unsigned int databit, const char *stopbit,char parity);


int usr_serial_open( char *port, unsigned int baudrate, 
                     unsigned int databit, const char *stopbit, char parity)
{
    int err;
    
    fd = open (port, O_RDWR | O_NOCTTY | O_NDELAY);
    if (-1 == fd) {
        fprintf(stderr, "cannot open port %s\n", port);
        return (-1);
    }
    
    tcgetattr (fd, &termios_old);       /* save the form termios value */
      
    err = set_portattr (baudrate, databit, stopbit, parity);
    if ( err ) {
        fprintf ( stderr, "\nport %s cannot set baudrate at %d\n",
                  port, baudrate);
    }
    usr_baudrate = baudrate;
    
    return fd;
}

void usr_serial_close( void )
{
    /* flush output data before close and restore old attribute */
    tcsetattr(fd, TCSADRAIN, &termios_old);
    close(fd);
}

unsigned int usr_serial_sendbytes (void * data, unsigned int datalength)
{
    unsigned int total_len = 0;
    
    total_len = write(fd, data, datalength);

    return (total_len);
}

int usr_serial_readbytes (void *data, unsigned int datalength)
{
    unsigned int total_len = 0;
    total_len = read(fd, data, datalength);
    if (total_len > 0) {
        printf("Receive %d bytes: %.*s\n", total_len, (char*)data);
    }

    return (total_len);
}

unsigned int usr_serial_readinterrupt (void *data, unsigned int datalength)
{
    int total_len = 0;

    /**
     * caculate the time of 5 characters and get the maxim
     * with 3ms and 5 ch's time
    */
    tv_timeout.tv_sec = 0;
    tv_timeout.tv_usec = ( (CH_TO_WAIT * CH_BITS) * (1000000/usr_baudrate));

    while(1){
        FD_ZERO (&fs_read);
        FD_SET (fd, &fs_read);
        select (fd + 1, &fs_read, NULL, NULL, &tv_timeout);
        
        total_len = read(fd, data, datalength);
        if (total_len > 0) {
            printf("Receive %d bytes: %.*s\n", total_len, (char*)data);
            return total_len;
        }
    }

    return total_len;

}

static void set_data_bit (unsigned int databit)
{
    termios_new.c_cflag &= ~CSIZE;
    switch (databit) {
    default:
    case 8:
        termios_new.c_cflag |= CS8;
        break;
    case 7:
        termios_new.c_cflag |= CS7;
        break;
    case 6:
        termios_new.c_cflag |= CS6;
        break;
    case 5:
        termios_new.c_cflag |= CS5;
        break;
    }
}

static void set_stopbit (const char *stopbit)
{
    if (0 == strcmp (stopbit, "1")) {
        termios_new.c_cflag &= ~CSTOPB;    /* 1 stop bit */
    }
    else if (0 == strcmp (stopbit, "1.5")) {
        termios_new.c_cflag &= ~CSTOPB;     /* 1.5 stop bits */
    }
    else if (0 == strcmp (stopbit, "2")) {
        termios_new.c_cflag |= CSTOPB;       /* 2 stop bits */
    }
    else {
        termios_new.c_cflag &= ~CSTOPB;     /* 1 stop bit */
    }
}

static void set_parity (char parity)
{
    switch (parity) {
    case 'N':                  /* no parity check */
        termios_new.c_cflag &= ~PARENB;
        break;
    case 'E':                  /* even */
        termios_new.c_cflag |= PARENB;
        termios_new.c_cflag &= ~PARODD;
        break;
    case 'O':                  /* odd */
        termios_new.c_cflag |= PARENB;
        termios_new.c_cflag |= ~PARODD;
        break;
    default:                   /* no parity check */
        termios_new.c_cflag &= ~PARENB;
        break;
    }
}

static speed_t baudrate_to_Bxx (unsigned int baudrate)
{
    switch (baudrate) {
    case 0:
        return (B0);
    case 50:
        return (B50);
    case 75:
        return (B75);
    case 110:
        return (B110);
    case 134:
        return (B134);
    case 150:
        return (B150);
    case 200:
        return (B200);
    case 300:
        return (B300);
    case 600:
        return (B600);
    case 1200:
        return (B1200);
    case 2400:
        return (B2400);
    case 9600:
        return (B9600);
    case 19200:
        return (B19200);
    case 38400:
        return (B38400);
    case 57600:
        return (B57600);
    case 115200:
        return (B115200);
    default:
        return (B9600);
    }
}

static void set_baudrate (unsigned int baudrate)
{
    speed_t speed;
    
    speed = baudrate_to_Bxx (baudrate);  /* set baudrate */
    cfsetispeed(&termios_new, speed);    // set input speed
    cfsetospeed(&termios_new, speed);    // set output speed
}

static unsigned int set_portattr ( unsigned int baudrate,  // 1200 2400 4800 9600 .. 115200
                                   unsigned int databit,   // 5, 6, 7, 8
                                   const char *stopbit,    //  "1", "1.5", "2"
                                   char parity)            // N(o), O(dd), E(ven)
{
    bzero(&termios_new, sizeof (termios_new));
    cfmakeraw (&termios_new);

    set_baudrate (baudrate);
    
    termios_new.c_cflag |= CLOCAL | CREAD;   /* | CRTSCTS */
    
    set_data_bit (databit);
    set_parity (parity);
    set_stopbit (stopbit);
 
    termios_new.c_cc[VTIME] = 1;            /* unit: 1/10 second. */
    termios_new.c_cc[VMIN]  = 255;          /* minimal characters for reading */
    
    return (tcsetattr (fd, TCSANOW, &termios_new));
}



/* End of this file */

3.1 usr_serial.h 文件内容

#ifndef __USR_SERIAL_H
#define __USR_SERIAL_H

#include <termios.h>            /* tcgetattr, tcsetattr */
#include <stdio.h>              /* perror, printf, puts, fprintf, fputs */
#include <unistd.h>             /* read, write, close */
#include <fcntl.h>              /* open */
#include <sys/signal.h>
#include <sys/types.h>
#include <string.h>             /* bzero, memcpy */
#include <limits.h>             /* CHAR_MAX */

#ifdef __cplusplus
extern "C" {
#endif

int usr_serial_open( char *port, unsigned int baudrate, unsigned int databit, const char *stopbit, char parity);
void usr_serial_close( void );

unsigned int usr_serial_sendbytes (void * data, unsigned int datalength);
int usr_serial_readbytes (void *data, unsigned int datalength);
unsigned int usr_serial_readinterrupt (void *data, unsigned int datalength);

#ifdef __cplusplus
}
#endif

#endif /* __USR_SERIAL_H */