>this is problematic.
>
>you cannot add a new element before the pending firing because you can't
>tell how far into the present trigger you are.
This is not a problem for readable counters like the i8254. The problem
for the i8254 is that reading and writing it takes a long time (perhaps
5 usec each). Every write to it will decrease its accuracy (perhaps by 1
usec after careful calibration). Thus if the i8254 is used for generating
non-periodic interrupts with an average period of 333 usec, it may take
15/333 of the CPU (estimate another 5 usec for interrupt handling), and if
it is also used for timecounting then it may drift by 333 usec/second.
Bruce
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