avoid lost timer interrupts. Previous optimization attempt doing it only
for intervals less then 5000 ticks (~300us) reported to be unreliable by
some people. Probably because of some heavy SMI code on their boards.
Introduce additional safety interval of 128 counter ticks (~9us) between
programmed comparator and counter values to cover different cases of
delayed write found on some chipsets.
Approved by: re (kib)