发送AT\r后无回应？

CHB1948 2007-8-16 13:41 楼主

我的程序如下：
程序阻塞在read函数中，不能返回......

#include
#include
#include
#include
#include

// Set baud rate
int set_speed(int fd, speed_t speed)
{
struct termios opt;

tcgetattr(fd, &opt);
tcflush(fd, TCIOFLUSH);

cfsetispeed(&opt, speed);
cfsetospeed(&opt, speed);
if (tcsetattr(fd, TCSANOW, &opt) != 0)
{
      perror("tcsetattr\n");
      return 0;
}

tcflush(fd, TCIOFLUSH);
return 1;
}

// Set data bits, stop bits, and parity
int set_parity(int fd, int databits, int parity, int stopbits)
{
struct termios opt;
if (tcgetattr(fd, &opt) != 0)
{
      perror("tcgetattr\n");
      return 0;
}

opt.c_cflag &= ~CSIZE;
switch (databits)
{
      case 7:
         opt.c_cflag |= ~CS7;
         break;
      case 8:
         opt.c_cflag |= ~CS8;
         break;
      default:
         fprintf(stderr, "Unsupported data bits\n");
         return 0;
}

switch (parity)
{
      case 'n':
      case 'N':
         opt.c_cflag &= ~PARENB;
         opt.c_iflag &= ~INPCK;
         break;
      case 'o':
      case 'O':
         opt.c_cflag |= (PARODD | PARENB);
         opt.c_iflag |= INPCK;
         break;
      case 'e':
      case 'E':
         opt.c_cflag |= PARENB;
         opt.c_cflag &= ~PARODD;
         opt.c_iflag |= INPCK;
         break;
      case 'S':
      case 's':
         opt.c_cflag &= ~PARENB;
         opt.c_cflag &= ~CSTOPB;
         break;
      default:
         fprintf(stderr, "Unsupported parity.\n");
         return 0;
}

switch(stopbits)
{
      case 1:
         opt.c_cflag &= ~CSTOPB;
         break;
      case 2:
         opt.c_cflag |= CSTOPB;
         break;
      default:
         fprintf(stderr, "Unsupported stop bits\n");
         return 0;
}

tcflush(fd, TCIFLUSH);
if (tcsetattr(fd, TCSANOW, &opt) != 0)
{
      perror("tcsetattr\n");
      return 0;
}

return 1;
}

int main()
{
int fd = open("/dev/modem", O_RDWR | O_NOCTTY | O_NDELAY);

if (fd == -1)
{
      printf("Can't open /dev/modem\n");
      return -1;
}

struct termios opt;

// Set terminal attribute
fcntl(fd, F_SETFL, 0);
tcgetattr(fd, &opt);
opt.c_cflag |= (CLOCAL | CREAD);
opt.c_iflag &= ~( ICANON | ECHO | ECHOE | ISIG);
opt.c_oflag &= ~OPOST;
opt.c_cc[VMIN] = 0;
opt.c_cc[VTIME] = 10;
tcsetattr(fd, TCSANOW, &opt);

// Set speed
if (set_speed(fd, B115200) == 0)
{
      fprintf(stderr, "Set speed failed.\n");
      return -1;
}

// Set databits, parity, stopbits
if (set_parity(fd, 8, 'N', 1) == 0)
{
      fprintf(stderr, "Set parity failed.\n");
      return -1;
}

char buf[128] = {0};
strcpy(buf, "AT\r");
int  len = strlen(buf);
if (len != write(fd, buf, len))
{
      printf("Write failed.\n");
      return -1;
}

printf("About to read...\n");
len = read(fd, buf, 2);
printf("Read %d bytes.\n", len);
buf[len] = 0;
printf("buf = %s\n", buf);

close(fd);
return 0;
}