From owner-freebsd-hackers Sat Nov 18 09:07:19 1995 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.6.12/8.6.6) id JAA07057 for hackers-outgoing; Sat, 18 Nov 1995 09:07:19 -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 JAA07046 for ; Sat, 18 Nov 1995 09:07:15 -0800 Received: from ernie by casparc.ppp.net with uucp (Smail3.1.28.1 #1) id m0tGqeQ-000I1MC; Sat, 18 Nov 95 18:02 MET Received: by ernie.altona.hamburg.com (Smail3.1.29.1 #3) id m0tGpbM-00001PC; Sat, 18 Nov 95 16:54 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 16:54:48 +0100 (MET) 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 Reply-To: hm@altona.hamburg.com X-Mailer: ELM [version 2.4 PL24] Content-Type: text Content-Length: 842 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 > > >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). > > I think this only works reliably for 8MHz ISA buses. Exactly - it works on ISA and EISA machines but not necessarily on PCI. hellmuth -- Hellmuth Michaelis hm@altona.hamburg.com Hamburg, Europe (A)bort, (R)etry, (I)nstall BSD ?