Date: Wed, 14 Jul 1999 15:54:22 +0900 From: Seigo Tanimura <tanimura@naklab.dnj.ynu.ac.jp> To: dfr@nlsystems.com Cc: Seigo Tanimura <tanimura@naklab.dnj.ynu.ac.jp> Subject: Re: Rewriting pca(4) using finetimer(9) (was: Re: MPU401 now worksunder New Midi Driver Framework with a Fine Timer) Message-ID: <199907140654.PAA04958@rina.naklab.dnj.ynu.ac.jp> In-Reply-To: Your message of "Thu, 8 Jul 1999 09:54:42 %2B0100 (BST)" References: <Pine.BSF.4.10.9907080952480.558-100000@salmon.nlsystems.com>
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On Thu, 8 Jul 1999 09:54:42 +0100 (BST), Doug Rabson <dfr@nlsystems.com> said: 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. I have been reading the i8254 data sheet for another couple of days, to find a new problem. If we have a callout to be made before the timer fires, the counter needs to be reprogrammed with a new value. We cannot reload the new counter value immediately; an i8254 does not load the new value until the currrent period finishes (ie the timer fires) or the gate rises. Thus a callout will have an average delay of 0.5/hz = 50ms. This is too long for a timeout in microseconds. 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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