On Thu, 8 Jul 1999, Seigo Tanimura wrote: > On Wed, 7 Jul 1999 19:46:38 -0700 (PDT), > Julian Elischer <jul...@whistle.com> said: > > julian> With your scheme the clock needs to be always running at elevated > speed. > julian> Possibly you might have a startup routine that turns on the elevated > julian> frequency, (basically does an 'aquire_timer0()' ) I would say that > you > julian> would have more success in implementing your finetimer() by using > julian> "aquiretimer0" than the other way around. > > I agree that acquire_timer0() would give more freedom to the ticks > to callout. Then I tried figuring out how to manage multiple > callouts using acquire_timer0(), which is something like below. > > > Let C the callout queue, and c_i a callout. (0 <= i < I) Next define f(c_i) as > the callout function of c_i, and dt_rem(c_i) the time span between c_(i-1) and > c_i. (dt_rem(c_-1) is defined as zero) We use the time span to avoid > traversing > though the queue to update the time tags on the callouts. > > (footnote: I'd better write in TeX :-<) > > Queueing a new callout c' to be made in t' involves a problem to find the > maximum j (which is an integer, j >= 0) satisfying a constraint > > t' > \sum_(k=0)^(j) dt_rem(c_k) > > where the right hand side of the inequality is the time span after which > the callout c_k is made. Then c' is inserted after c_j and new dt_rem(c_(j+1)) > and dt_rem(c_(j+2)) are determined. Now we can acquire_timer0() with > dt_rem(c_0). > > In clkintr(), we dequeue c_0 from C, and make a callout to f(c_0). Then > acquire_timer0() is called once more with the new dt_rem(c_0). dt_rem(c_i) is > the difference of callout times, so they need not be updated on every > clkintr(). > > > Although the computational cost in clkintr() is generaly O(1), the queueing > cost > is O(I). Not sure whether we can reduce it or not (will it really make a > trouble?) > > > How does it sound?
If I understand this correctly, you are suggesting that we program timer0 so that we only take interrupts when a finetimer is due to fire? If so, then it sounds very good. The idea of taking 6000+ interrupts/sec made me uneasy, even though most would return without doing any work. -- Doug Rabson Mail: d...@nlsystems.com Nonlinear Systems Ltd. Phone: +44 181 442 9037 To Unsubscribe: send mail to majord...@freebsd.org with "unsubscribe freebsd-hackers" in the body of the message
