From owner-freebsd-small Wed Jan 19 11:59:54 2000 Delivered-To: freebsd-small@freebsd.org Received: from freeby.mesanet.com (pm3-3-33.dynamic.idiom.com [216.240.35.129]) by hub.freebsd.org (Postfix) with ESMTP id 8B7E314E26 for ; Wed, 19 Jan 2000 11:59:51 -0800 (PST) (envelope-from pcw@mesanet.com) Received: from localhost (localhost [127.0.0.1]) by freeby.mesanet.com (8.8.7/8.8.7) with ESMTP id LAA05396 for ; Wed, 19 Jan 2000 11:59:32 -0800 (PST) Date: Wed, 19 Jan 2000 11:59:32 -0800 (PST) From: "Peter C. Wallace" To: freebsd-small Subject: Re: PC/104 In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-small@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Wed, 19 Jan 2000, Mike Nowlin wrote: > > > One additional difference is that PC/104 supports IRQ sharing (across > > different devices on the bus). I don't remember the details > something about impedance and pull-up/down> > > I've been kinda wondering about this for a while.... From everything I've > been able to find, it's not the ISA bus itself that causes problems with > sharing IRQ's, but it's the cheap cards we're so used to seeing everywhere > that don't use open-collector drivers. I have successfully shared > interrupts using old (bulky, lots of chips, sucks up lots of power) cards > in the past, but the modern stuff hates it. > > Any input? > > mike Actuallly open collector does you no good because IBM in their great wisdom made the IRQ polarity active high (and edge triggered to boot). If you put a pull-down on the IRQ bus (contrary to standard practice) you can use an "open source" driver easily done in a PAL. We do this on some of our PC/104 cards but basically its M^2 logic... > > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-small" in the body of the message > Peter Wallace Mesa Electronics To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-small" in the body of the message