Date: Sun, 28 Sep 1997 11:16:14 +0200 (CEST) From: hm@kts.org (Hellmuth Michaelis) To: tony@dell.com (Tony Overfield) Cc: tlambert@primenet.com, hackers@FreeBSD.ORG Subject: Re: INB question Message-ID: <m0xFFSY-00023ZC@bert.kts.org> In-Reply-To: <3.0.2.32.19970928015842.006ce080@bugs.us.dell.com> from Tony Overfield at "Sep 28, 97 01:58:42 am"
index | next in thread | previous in thread | raw e-mail
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)
help
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?m0xFFSY-00023ZC>