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From: nelson@crynwr.com (Russell Nelson)
Newsgroups: comp.unix.bsd
Subject: Ethernet card
Message-ID: <713928805snx@crynwr.com>
Date: 16 Aug 92 07:29:00 GMT
References: <1992Aug14.150906.1614@rwwa.COM>
Organization: Crynwr Software
Lines: 26
In article <1992Aug14.150906.1614@rwwa.COM> witr@rwwa.com writes:
In article <michaelv.713756052@test.cc.iastate.edu>,
michaelv@iastate.edu (Michael L. VanLoon) writes:
| Once again: IRQ 2 is _unavailable_ in an AT. [...] Your card,
| intelligently, reassigns IRQ 2 requests to IRQ 9 if it's put into an
| AT.
Not entirely correct. The IRQ2 pin (fourth pin from the rear, non
component side), is *physically* connected to the IRQ9 signal, which
is connected to the second PIC. (It is true that the second PIC chains
to the first one throught the IRQ2 signal.) The *software* ``reassigns''
the interrupt by diddling the second PIC instead of the first when
it notices that the card was set to interrupt on IRQ2.
Yes, Michael's explanation is less than clear.
Some software is smart, and captures IRQ9 if you tell it to use IRQ2.
Some software is stupid, and captures IRQ2 if you configure your
interrupt handler for IRQ2. This still works under DOS because the
default IRQ9 interrupt handler acknowledges the interrupt on the
second PIC, and fakes an IRQ2 interrupt.
I don't know if 386BSD is as smart as DOS...
-russ <nelson@crynwr.com> I'm proud to be a humble Quaker!
Crynwr Software Crynwr Software sells packet driver support.
11 Grant St. 315-268-1925 Voice
Potsdam, NY 13676 315-268-9201 FAX