From owner-freebsd-hackers Sun Sep 28 02:32:54 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id CAA22239 for hackers-outgoing; Sun, 28 Sep 1997 02:32:54 -0700 (PDT) Received: from casparc.ppp.net (mail.ppp.net [194.64.12.35]) by hub.freebsd.org (8.8.7/8.8.7) with SMTP id CAA22234 for ; Sun, 28 Sep 1997 02:32:42 -0700 (PDT) Received: from ernie by casparc.ppp.net with uucp (Smail3.1.28.1 #1) id m0xFFhq-000oJZC; Sun, 28 Sep 97 10:32 MET Received: from bert.kts.org(really [194.55.156.2]) by ernie.kts.org via sendmail with smtp id for ; Sun, 28 Sep 1997 11:24:21 +0200 (MET DST) (Smail-3.2.0.91 1997-Jan-14 #2 built 1997-Feb-8) Received: by bert.kts.org via sendmail with stdio id for hackers@FreeBSD.ORG; Sun, 28 Sep 1997 11:16:14 +0200 (CEST) (Smail-3.2.0.94 1997-Apr-22 #7 built 1997-Jul-4) Message-Id: From: hm@kts.org (Hellmuth Michaelis) Subject: Re: INB question In-Reply-To: <3.0.2.32.19970928015842.006ce080@bugs.us.dell.com> from Tony Overfield at "Sep 28, 97 01:58:42 am" To: tony@dell.com (Tony Overfield) Date: Sun, 28 Sep 1997 11:16:14 +0200 (CEST) Cc: tlambert@primenet.com, hackers@FreeBSD.ORG Organization: Kitchen Table Systems Reply-To: hm@kts.org X-Mailer: ELM [version 2.4ME+ PL31H (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG X-Loop: FreeBSD.org Precedence: bulk Tony Overfield wrote: > Port 0x84 is an unused DMA page register, just like 0x80, 0x85, 0x86 > and others. Each of these unused registers is read/write and should > have no effect, except to cause an 8-bit ISA I/O cycle. This might be on some (or even the majority) motherboards, but not on all: some existing chipsets seem to detect accesses to "unused" register addresses and prevent the i/o cycle to happen. I had exactly this problem in pcvt, and for the majority of cases the i/o read to 0x84 ran without problems but on some platforms you'll get strange behaviours (see /usr/src/sys/i386/isa/pcvt/pcvt_hdr.h, around line 1364, "#if PCVT_PORTIO_DELAY"). hellmuth -- Hellmuth Michaelis hm@kts.org Hamburg, Europe "Those who can, do. Those who can't, talk. And those who can't talk, talk about talking." (B. Shaw)