c - tcsendbreak() 中的持续时间单位是什么？

Question

来自几乎所有的 Linux 联机帮助页 termios(3):

tcsendbreak() transmits a continuous stream of zero-valued bits for a specific duration, if the terminal is using asynchronous serial data transmission. If duration is zero, it transmits zero-valued bits for at least 0.25 seconds, and not more that 0.5 seconds. If duration is not zero, it sends zero-valued bits for some implementation-defined length of time.

If the terminal is not using asynchronous serial data transmission, tcsendbreak() returns without taking any action.

那么，“一些实现定义的时间长度”究竟是什么？

Answer 1

在 Linux 上，它是毫秒。

来自您引用的同一联机帮助页:

The effect of a nonzero duration with tcsendbreak() varies. SunOS specifies a break of duration * N seconds, where N is at least 0.25, and not more than 0.5. Linux, AIX, DU, Tru64 send a break of duration milliseconds. FreeBSD and NetBSD and HP-UX and MacOS ignore the value of duration. Under Solaris and UnixWare, tcsendbreak() with nonzero duration behaves like tcdrain()

可以看到出处here .

它正在调用 __ioctl (fd, TCSBRKP, (duration + 99)/100);，并且 TCSBRKP 本身会发送 arg 的中断十分之一秒，如 tty_ioctl(4) 联机帮助页中所述。