in generators/pps_gen_parport.c [167:177]
static inline ktime_t next_intr_time(struct pps_generator_pp *dev)
{
struct timespec64 ts;
ktime_get_real_ts64(&ts);
return ktime_set(ts.tv_sec +
((ts.tv_nsec > 990 * NSEC_PER_MSEC) ? 1 : 0),
NSEC_PER_SEC - (send_delay +
dev->port_write_time + 3 * SAFETY_INTERVAL));
}