Previous adjtime() implementation was limited to adjusting system
timer tick period. This commit reimplements the internals to use
a kernel watchdog timer. Platform-independent part of the code now
works also for adjusting hires RTC and tickless timer rate.
User code facing API is unchanged. Architecture code API has changed:
up_adj_timer_period() is replaced by up_adjtime().
Other improvements:
- Support query of remaining adjustment by passing NULL to first
argument of adjtime(). This matches Linux behavior.
- Improve resolution available for architecture driver, previously
limited to 1 microsecond per tick. Now 1 nanosecond per second.
1) Previously adjustments less than 1 microsecond per tick would be
completely ignored. Now they are applied over a shorter period at
a rate of 1 us per tick.
2) Previously CLOCK_ADJTIME_PERIOD was in units of 1/100th of second.
Change to milliseconds to be more generally useful unit.
Change setting name to CLOCK_ADJTIME_PERIOD_MS to make the unit change
easier to notice.
3) Previously CLOCK_ADJTIME_SLEWLIMIT was in percentage.
Most clock crystals have better accuracy than 1%, so the minimum slew
rate was excessive. Change to CLOCK_ADJTIME_SLEWLIMIT_PPM with setting
value in parts per million.
4) No need to use floating point math in clock_adjtime.c.
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>
Petteri Aimonen