请教一个串口read函数的问题

kandx

用read读取串口的数据，部分代码如下：
       int fd;
          int bytes;
          unsigned char buff[128];
          fd=open("/dev/ttyS0", O_RDWR|O_NDELAY|O_NOCTTY);
          if(fd!=1)
          {
                 .......
                 bytes=read(fd, buff, 128);
                 ......
           }
每读一次，bytes的值都是8，是不是每次最多只能读取8个字节？或者，能不能让它一次读取超过8个字节？哪位知道的请指教，谢谢！

friday182

低手的见解：
可能是c_lflag设置成non-canonical的了吧，看看你是怎么设置的？下面是从Serial-Programming-HOWTO copy的一段
In non-canonical input processing mode, input is not assembled into lines and input processing (erase, kill, delete, etc.) does not occur. Two parameters control the behavior of this mode: c_cc[VTIME] sets the character timer, and c_cc[VMIN] sets the minimum number of characters to receive before satisfying the read.

If MIN > 0 and TIME = 0, MIN sets the number of characters to receive before the read is satisfied. As TIME is zero, the timer is not used.

If MIN = 0 and TIME > 0, TIME serves as a timeout value. The read will be satisfied if a single character is read, or TIME is exceeded (t = TIME *0.1 s). If TIME is exceeded, no character will be returned.

If MIN > 0 and TIME > 0, TIME serves as an inter-character timer. The read will be satisfied if MIN characters are received, or the time between two characters exceeds TIME. The timer is restarted every time a character is received and only becomes active after the first character has been received.

If MIN = 0 and TIME = 0, read will be satisfied immediately. The number of characters currently available, or the number of characters requested will be returned. According to Antonino (see contributions), you could issue a fcntl(fd, F_SETFL, FNDELAY); before reading to get the same result.

By modifying newtio.c_cc[VTIME] and newtio.c_cc[VMIN] all modes described above can be tested.

realtang

这是读真实串口，又不是虚拟终端或者vt100终端。绝对应该采用non-canonical（非行规）。
至于只返回8个字节，我觉得是你的串口外设的问题。他的数据锁存器也许是只有64位的。
要不就是串口接口控制器驱动的问题，查查内核的串口源文件，看看它是否把串口的input buffer只设置为了最大64位。

realtang

好消息啊，我找到了你想要的。
首先打开设备不能采用O_NDELAY选项，
另外要通过tcsetchar()设置Control Characters里面的VMIN为128。另外再设置一个足够等到这128位数据的时间VTIME。
如此，就ok了。

半杯可乐

O_NDELAY方式打开的话，会不会阻塞死了？