FT(4)               UNIX Programmer's Manual                FT(4)

NAME
     ft - fake interval timer

DESCRIPTION
     _F_t is a pseudo-device that makes it possible to simulate an
     _a_l_a_r_m(2) call with better than 1 second resolution.

     To use the interval timer, open one of the files /_d_e_v/_f_t?.
     This opens the interval timer for exclusive use; an attempt
     by another process to open the timer will fail with error
     indication EBUSY in _e_r_r_n_o - see _i_n_t_r_o(2).  The resulting
     file descriptor can be the argument of an _i_o_c_t_l(2) call:

       #include <sgtty.h>

       struct   requestbuf {
           short     time;
           short     signo;
       } request;

       ioctl(fildes, FTIOCSET, (struct sgttyb *) &request);

     After _t_i_m_e clock cycles (fiftieths or sixtieths of a
     second), a signal of type _s_i_g_n_o will be sent to the request-
     ing process.  The requested _t_i_m_e may not exceed 60 seconds
     (if longer delays are required the real _a_l_a_r_m(2) call should
     be used).  The _i_o_c_t_l(2) call

       ioctl(fildes, FTIOCCANCEL, (struct sgttyb *) NULL);

     cancels any outstanding interrupt request.

FILES
     /dev/ft?

SEE ALSO
     alarm(2), ioctl(2)

BUGS
     An FTIOCCANCEL request prevents the signal from being sent
     when the interval has expired, but does not actually cancel
     the timeout request.  It cannot be followed by a new
     FTIOCSET request until the original delay has expired.

Printed 7/31/83                                                 1