From owner-freebsd-hackers Sat Nov 18 05:07:21 1995 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.6.12/8.6.6) id FAA20821 for hackers-outgoing; Sat, 18 Nov 1995 05:07:21 -0800 Received: from casparc.ppp.net (casparc.ppp.net [194.64.12.35]) by freefall.freebsd.org (8.6.12/8.6.6) with SMTP id FAA20802 for ; Sat, 18 Nov 1995 05:07:11 -0800 Received: from ernie by casparc.ppp.net with uucp (Smail3.1.28.1 #1) id m0tGmuA-000I54C; Sat, 18 Nov 95 14:02 MET Received: by ernie.altona.hamburg.com (Smail3.1.29.1 #3) id m0tGmXL-00001XC; Sat, 18 Nov 95 13:38 MET Message-Id: From: hm@altona.hamburg.com (Hellmuth Michaelis) Subject: Re: DELAY's in syscons To: bde@zeta.org.au (Bruce Evans) Date: Sat, 18 Nov 1995 13:38:27 +0100 (MET) Cc: freebsd-hackers@freebsd.org, hosokawa@mt.cs.keio.ac.jp In-Reply-To: <199511181058.VAA20290@godzilla.zeta.org.au> from "Bruce Evans" at Nov 18, 95 09:58:46 pm Reply-To: hm@altona.hamburg.com X-Mailer: ELM [version 2.4 PL24] Content-Type: text Content-Length: 847 Sender: owner-hackers@freebsd.org Precedence: bulk >From the keyboard of Bruce Evans: > DELAY(n) only delays n-20 usec on an infinitely fast machine so it > shouldn't be called with n <= 20 unless the precise delay doesn't matter. > Syscons and pcvt call it with delays <= 10 usec when the precise delay > does matter. If not told otherwise, pcvt does NOT use DELAY() for exactly the reason you just describe. 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). hellmuth -- Hellmuth Michaelis hm@altona.hamburg.com Hamburg, Europe (A)bort, (R)etry, (I)nstall BSD ?