*BSD News Article 73838


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From: j@uriah.heep.sax.de (J Wunsch)
Newsgroups: comp.unix.bsd.freebsd.misc
Subject: Re: what is MCD0?
Date: 15 Jul 1996 22:34:13 GMT
Organization: Private BSD site, Dresden
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nichols@ccwf.cc.utexas.edu (Stewart Nichols) wrote:

> I've had interference from the mcd driver, also.  I think the original
> poster was actually asking, in effect, "Why does this mcd0 device, which 
> doesn't seem to exist in my machine, mess up my network card driver?".
> 
> If someone who knows something about how the probes are done would
> be willing to explain it, I would be interested in knowing how the
> probes are performed.

Because it's ISA.

ISA is not a bus system, it's a plain disease.  It resembles the bus
systems of the micros of the early 80's running CP/M.  It's an almost
``CPU local bus'', with only some wait states added for several bus
access operations.  No per-slot configuration registers or memory
areas.  Autoprobing was apparently not an issue for a CP/M system, you
had to use a customized BIOS anyway.

The formula is simple: any attempt to auto-probe some device on the
ISA bus that requires even a single write operation to the bus is
destructive.  Even if you finally found out that the probed address
doesn't belong to `your' device, you cannot undo you ramifications,
leaving the actual device you were just stomping upon in a weird
state.

That's why the recommendation: make sure where your hardware is, and
use the -c option to disable all unused drivers, and adjust the used
drivers to match the reality.  Everything else is a hazardous game.

-- 
cheers, J"org

joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)