如何在C中检查串行新消息

Question

我必须制作一个程序，从某个服务器获取串口命令，我必须将此命令转发给三个设备。其中一个设备将发送答案，其他所有设备都不会发送任何内容。问题是，如何检查新邮件是否来自服务器？据我所知，如果我将不断采取零消息，我将加载CPU？或不？

这是代码，它重载了注释，但整个系统很容易。并且read（）函数不再起作用，因为我试图分别读取每个字符，直到\ n

    #include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
#include <time.h>

#define HE_BAUDRATE     B19200
#define HE_BUF          1024

#define ROO_TEMP        ROO_TEMP
#define ROO_DESI        ROO_DESI
#define ROO_DESI1       "09 SET ROO_DESI D 200"
#define ROO_DESI2       "09 SET SYS_DATE 17:52 18.04.14"

struct termios *he_tio_save;
struct termios tio;

int open_serial(const char *dev);
void close_serial(int fd);
int send_msg(int fd, unsigned char *data, int len);
int read_msg(int fd, unsigned char *buf, int len); 

const char *device0 = "/dev/ttyS0";
const char *device1 = "/dev/ttyS1"; 
const char *device2 = "/dev/ttyS2";
const char *device3 = "/dev/ttyS3";


int main() {
  int  fd0,fd1,fd2,fd3, ret = 0, ret1 = 0, ret2 = 0;
  char data[50], data_back[50];
  char command;
  unsigned char buf[HE_BUF], buf1[HE_BUF], buf2[HE_BUF];

  //Serielle Schnittschtellen oeffnen

  fd0 = open_serial(device0);
  fd1 = open_serial(device1);
  fd2 = open_serial(device2);

  if (fd0 < 0) {
    printf("Unable to open device %s\n", device1);
  }
  printf("Device0 opened\n");

    while (1){

    memset(buf, 0, HE_BUF);

    // Lesen vom server ANFANG
        ret = read_msg(fd0, buf, HE_BUF);
    if (ret == -1) { 
      printf("communication problem\n");
      ret = -1;
    }
    // Lesen vom server ANFANG

    strcpy(data,buf);

    // Senden an device1 ANFANG
    //fd1 = open_serial(device1);
    printf("1datatosend: %s\n", data);
    ret = send_msg(fd1, data, strlen(data));
    if (ret < 0) {
      ret = -1;
      printf("1Error while sending message\n");
    }
    // Senden an device1 ENDE
    // Lesen vom decvice1 ANFANG
    ret1 = read_msg(fd1, buf1, HE_BUF);
    if (ret1 == -1) { 
      printf("1communication problem\n");
      ret1 = -1;
    }
    //Lesen vom device1 ENDE
    //close_serial(fd1);

    // Senden an device2 ANFANG
    printf("2datatosend: %s\n", data);
    ret = send_msg(fd2, data, strlen(data));
    if (ret < 0) {
      ret = -1;
      printf("2Error while sending message\n");
    }
    // Senden an device2 ENDE
    // Lesen vom decvice2 ANFANG
    ret2 = read_msg(fd2, buf2, HE_BUF);
    if (ret2 == -1) { 
      printf("2communication problem\n");
      ret2 = -1;
    }
    //Lesen vom device2 ENDE
     memset(data_back, 0, 50);

    if (ret1 >= 0 ){
      strcpy(data_back,buf1);
    }
    if (ret2 >= 0 ){
      strcpy(data_back,buf2);
    }

    // Senden an server ANFANG
    printf("datatosend_back: %s\n", data_back);
    ret = send_msg(fd0, data_back, strlen(data_back));
    if (ret < 0) {
      ret = -1;
      printf("Error while sending message\n");
    }
    // Senden an server ENDE

    usleep(300000);
    fflush(stdout);
  }

  // Serial schliessen
  close_serial(fd0);
  close_serial(fd1);
  close_serial(fd2);

  return 0;                                                                            

}


int open_serial(const char *dev) {
    int fd;
    //struct termios tio;

    // Geraet oeffnen

    fd = open(dev, O_RDWR|O_NONBLOCK);

    // Alte Einstellungen sichern
    if (he_tio_save == NULL) { // 4.4.2009 J. Brenner
        he_tio_save = (struct termios *)malloc(sizeof(struct termios) + 4);
        // 4.4.2009 J. Brenner: 4 Bytes mehr alloziert, da valgrind feststellte
        // das tcgetattr() in einen nicht allozierten Bereich schreiben wollte.
        tcgetattr(fd, he_tio_save);
    }

    /* Neue Einstellungen setzen
     *
     * HE_BAUDRATE: Baudrate
     * CS8:         8 Datenbit, 1 Stopbit
     * PARENB:      Gerade Paritaet
     * CREAD:       Lesen ermoeglichen
     * CLOCAL:      Modemkontrolle deaktivieren
     *
     * IGNPAR:      Parityfehler ignorieren
     * IGNBRK:      Break ignorieren
     */
    memset(&tio, 0, sizeof(struct termios));
    tio.c_cflag = HE_BAUDRATE | CS8 | CREAD | CLOCAL;
    tio.c_iflag = IGNPAR | IGNBRK;
    tio.c_oflag = 0;
    tio.c_lflag = 0;
    tio.c_cc[VTIME] = 0;
    tio.c_cc[VMIN] = 1;
    tcflush(fd, TCIOFLUSH);
    tcsetattr(fd, TCSANOW, &tio);

    return fd;
}


void close_serial(int fd) {

    if (fd < 0)
        return;

    // Alte Einstellungen wiederherstellen
    tcsetattr(fd, TCSANOW, he_tio_save);
    tcflush(fd, TCIOFLUSH);

    close(fd);
    free(he_tio_save);
    he_tio_save = NULL; // 4.4.2009 J. Brenner

}


int send_msg(int fd, unsigned char *data, int len) {
    int ret = 0;


    // Daten schreiben
    ret = write(fd, data, len);
    printf("we send:#%s# length of %i\n",data,len);
    tcdrain(fd);

    return ret;
}

int read_msg(int fd, unsigned char *buf, int len) {
    int count, ret = 0;
    char c;

    // Daten lesen
    count = 0;
    do{
        ret = read(fd, &c, len);
        buf[count] = c;
        count += ret;
    } while (ret > 0 && buf[count] != '\n');
    ret = count;


    if (ret == -1) {
        printf("Error reading from Serial\n");
        printf("buf is empty\n");
        printf("buf:%s length of %i\n",buf,strlen(buf));
        printf("ret is %i\n",ret);
    }

    else {
        printf("Message received:\n");
        printf("buf:%s length of %i\n",buf,strlen(buf));
        printf("ret is %i\n",ret);

    }

    return ret;
}