I was looking into factoring out the common time-of-day clock code bits
in the sparc & sparc64  ports, and I decided to turn those bits into
a MI time-of-day clock driver.  I've written up a man page, todr(9),
and done a sample implementation for the Mostek MK48Txx and
Intersil 7170 chips.

Especially, the various Mostek models are used in a number of machines
so there's a potential to share some code here.

I plan to move the sparc64 port over to use the new mk48txx driver
soon (it's easiest), then take on the sparc port (as soon as the
Intersil driver is ready).

In the mean time, I invite you to look over the interface and check
it for sanity, usability etc.

Xrefs: todr(9), mk48txx(4), intersil7170(4),
       sys/dev/clock_subr.h, sys/dev/ic/mk48txx.c, sys/dev/ic/intersil7170.c
-pk