From owner-freebsd-hackers Sat Nov 18 13:43:35 1995 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.6.12/8.6.6) id NAA19370 for hackers-outgoing; Sat, 18 Nov 1995 13:43:35 -0800 Received: from phaeton.artisoft.com (phaeton.Artisoft.COM [198.17.250.211]) by freefall.freebsd.org (8.6.12/8.6.6) with ESMTP id NAA19365 for ; Sat, 18 Nov 1995 13:43:29 -0800 Received: (from terry@localhost) by phaeton.artisoft.com (8.6.11/8.6.9) id OAA09716; Sat, 18 Nov 1995 14:40:55 -0700 From: Terry Lambert Message-Id: <199511182140.OAA09716@phaeton.artisoft.com> Subject: Re: DELAY's in syscons To: bde@zeta.org.au (Bruce Evans) Date: Sat, 18 Nov 1995 14:40:55 -0700 (MST) Cc: bde@zeta.org.au, hm@altona.hamburg.com, freebsd-hackers@FreeBSD.ORG, hosokawa@mt.cs.keio.ac.jp In-Reply-To: <199511181324.AAA25738@godzilla.zeta.org.au> from "Bruce Evans" at Nov 19, 95 00:24:23 am X-Mailer: ELM [version 2.4 PL24] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 920 Sender: owner-hackers@FreeBSD.ORG Precedence: bulk > >Instead it uses dummy reads from port 0x84 which execute in a defined time > >of ~= 1,25us. (IF they ever do execute - i was told that some implementations > >do know that there is nothing to read from port 0x84 and somehow don't let > >this read though to the bus, the result is, that these reads do execute very > >fast). > > I think this only works reliably for 8MHz ISA buses. Otherwise I would > have used it in DELAY(). The only way it can be reliable is if all buses > know it is special and put something there that inserts wait states to > extend the i/o time to 1.25us. Time to scream about high resoloution kernel timers once again? A nice reschedulable one-shot HRT interface would fix DELAY right up. There are only *minor* kernel preemption issues involved. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.