This commit adds Linux like adjtime() interface that is used to correct
the system time clock if it varies from real value. The adjustment is
done by slight adjustment of clock period and therefore the adjustment
is without time jumps (both forward and backwards)
The implementation is enabled by CONFIG_CLOCK_ADJTIME and separated from
CONFIG_CLOCK_TIMEKEEPING functions. Options CONFIG_CLOCK_ADJTIME_SLEWLIMIT
and CONFIG_CLOCK_ADJTIME_PERIOD can be used to control the adjustment
speed.
Interfaces up_get_timer_period() and up_adj_timer_period() has to be
defined by architecture level support.
This is not a POSIX interface but derives from 4.3BSD, System V.
It is also supported for Linux compatibility.
Signed-off-by: Michal Lenc <michallenc@seznam.cz>
360e938fa6