Date: Thu, 08 Jul 1999 15:17:07 +0900 From: Seigo Tanimura <tanimura@naklab.dnj.ynu.ac.jp> To: julian@whistle.com Cc: Seigo Tanimura <tanimura@naklab.dnj.ynu.ac.jp> Subject: Re: Rewriting pca(4) using finetimer(9) (was: Re: MPU401 now works under New Midi Driver Framework with a Fine Timer) Message-ID: <199907080617.PAA23884@rina.naklab.dnj.ynu.ac.jp> In-Reply-To: Your message of "Wed, 7 Jul 1999 19:46:38 -0700 (PDT)" References: <Pine.BSF.3.95.990707193513.23943h-100000@current1.whistle.com>
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On Wed, 7 Jul 1999 19:46:38 -0700 (PDT), Julian Elischer <julian@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? Seigo Tanimura <tanimura@naklab.dnj.ynu.ac.jp> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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