From owner-freebsd-current Tue Jul 13 23:56: 5 1999 Delivered-To: freebsd-current@freebsd.org Received: from rina.naklab.dnj.ynu.ac.jp (rina.naklab.dnj.ynu.ac.jp [133.34.17.16]) by hub.freebsd.org (Postfix) with ESMTP id 25D8014DD4; Tue, 13 Jul 1999 23:55:56 -0700 (PDT) (envelope-from tanimura@naklab.dnj.ynu.ac.jp) Received: from rina.naklab.dnj.ynu.ac.jp (localhost [127.0.0.1]) by rina.naklab.dnj.ynu.ac.jp (8.9.1a/3.7W-Naklab-2.1-19981120) with ESMTP id PAA04958; Wed, 14 Jul 1999 15:54:22 +0900 (JST) Message-Id: <199907140654.PAA04958@rina.naklab.dnj.ynu.ac.jp> To: dfr@nlsystems.com Cc: julian@whistle.com, bde@zeta.org.au, freebsd-hackers@freebsd.org, freebsd-current@freebsd.org Cc: Seigo Tanimura Subject: Re: Rewriting pca(4) using finetimer(9) (was: Re: MPU401 now worksunder New Midi Driver Framework with a Fine Timer) From: Seigo Tanimura In-Reply-To: Your message of "Thu, 8 Jul 1999 09:54:42 +0100 (BST)" References: X-Mailer: Mew version 1.70 on Emacs 19.34.1 / Mule 2.3 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Date: Wed, 14 Jul 1999 15:54:22 +0900 Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Thu, 8 Jul 1999 09:54:42 +0100 (BST), Doug Rabson 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 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message