>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 To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
