因为今天做串口通讯的时候发现一个怪现象，在虚拟机rh9中的用串口程序通讯，居然只能收到16个字符长的数据，而我的read(fd,buf,31);就是说我要一次跟plc通讯收31个字符的串，这样读的是31但每回只能收16个，考虑到buf[1024]，而串口的缓存一定大于16btye的问题，想到问题可能出现在

newtio.c_cc[VTIME]    = 1；
newtio.c_cc[VMIN]  = 0；

这个地方，去官方看了下关于这个地方的说明：

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.

这样我们可以看出TIME是一个定时器而时间估计是100ms为单位，而MIN是一个字符间间植，

当我把

newtio.c_cc[VMIN]=0;
newtio.c_cc[VTIME]=31;

时发现31个的串可收，但如果其他的串小于31，串口会被中断堵塞

这样需要一个定时器来让他重新关闭，并把不足31的字符返回给buf里

所以可以写成

 newtio.c_cc[VMIN]=1;
 newtio.c_cc[VTIME]=31;

这样字符范围就在0-31之间的任意长度并在定时100ms内可以在次读去而不造成主塞现象

OK今天的一个小问题希望能给做arm 通讯的朋友一点帮助！