Philippe Gerum authored Feb 04, 2019 and Jan Kiszka committed Feb 04, 2019

clock_decrease_after_periodic_timer_first_tick checks that periodic
interval timers based on CLOCK_REALTIME are not (pathologically)
affected by the epoch going backwards.

To this end, we measure the actual time observed between two ticks of
a periodic timer based on CLOCK_REALTIME with a call to
clock_settime() injecting a negative offset in between, equivalent to
five ticks.

Due to processing delays induced by clock_settime() and other latency,
we could observe a duration which exceeds a tick by a few tenths of
microseconds. Since we can't anticipate the amount of latency
involved, let's accept a longer delay of at most two ticks.

This is still correct from the standpoint of the test, which verifies
that no correlation exists between the clock offset injected by
clock_settime() and the delay until the next tick generated by the
affected clock.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>