From owner-freebsd-current  Thu Jul  8  8:33: 8 1999
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To: Bruce Evans <bde@zeta.org.au>
Cc: dfr@nlsystems.com, tanimura@naklab.dnj.ynu.ac.jp,
	freebsd-current@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG,
	julian@whistle.com
Subject: Re: Rewriting pca(4) using finetimer(9) (was: Re: MPU401 now worksunder New Midi Driver Framework with a Fine Timer) 
In-reply-to: Your message of "Fri, 09 Jul 1999 01:27:14 +1000."
             <199907081527.BAA04078@godzilla.zeta.org.au> 
Date: Thu, 08 Jul 1999 17:31:48 +0200
Message-ID: <2663.931447908@critter.freebsd.dk>
From: Poul-Henning Kamp <phk@critter.freebsd.dk>
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Somebody should study the abilities of the on-cpu APIC for this
for pentium ff. machines.


In message <199907081527.BAA04078@godzilla.zeta.org.au>, Bruce Evans writes:
>>dfr> If I understand this correctly, you are suggesting that we program timer0
>>dfr> so that we only take interrupts when a finetimer is due to fire? If so,
>>dfr> then it sounds very good. The idea of taking 6000+ interrupts/sec made me
>>dfr> uneasy, even though most would return without doing any work.
>
>6000+ interrupts/sec is not many, unless it is done all the time.  A
>486/33 can handle about 50000 (16000 for pcaudio + 3 * 11520 for sio's).
>
>>There is one problem in this method. acquire_timer0() is only implemented
>>for i386. We would need to write something equivalent for alpha...
>
>This is a serious problem.  acquire_timer0() is currently disabled even
>for i386's when the i8254 is used for timecounting.  This is not hard
>to fix (the hooks into clkintr() work even better with timecounters
>since it is not necessary to resynchronise clock interrupts after a
>state change), but an i8254 interrupt frequency of 16000 Hz is too fast
>to be used routinely if the i8254 is being used for timecounting (even
>if the CPU can keep up with the interrupts, the overflow heuristics in
>i8254_get_timecount() may break down).  Other systems may have even
>more limitations on the timecounters.
>
>Bruce
>
>
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--
Poul-Henning Kamp             FreeBSD coreteam member
phk@FreeBSD.ORG               "Real hackers run -current on their laptop."
FreeBSD -- It will take a long time before progress goes too far!


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