Date: Tue, 29 Jul 1997 16:33:46 GMT From: mouth@ibm.net (John Kelly) To: FreeBSD Development <freebsd@atipa.com> Cc: hackers@FreeBSD.ORG, Terry Lambert <terry@lambert.org> Subject: Sharing interrupts (on ISA serial cards) Message-ID: <33de18a4.1100092@smtp-gw01.ny.us.ibm.net> In-Reply-To: <Pine.BSF.3.91.970728211925.25478B-100000@dot.ishiboo.com> References: <Pine.BSF.3.91.970728211925.25478B-100000@dot.ishiboo.com>
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On Mon, 28 Jul 1997 21:23:24 -0600 (MDT), you wrote: >You can share interrupts, but not use both SIMULTANEOUSLY. A very good >example would be to have LPT1: and a sound card on IRQ7 (both ISA). As >long as they have unique base addresses (0x378h and 0x220 for instance), >both devices can coexist. You just can't use them at the same time >without conflicting. Correct, and that is true when you have tri-state drivers on both devices and you do not have both open at the same time. > Sharing IRQs is definitely not recommend, but I believe your statement may > require a bit more qualifying. I'm only talking about two or more ISA serial adapters sharing the same interrupt. I'm not talking about two different types of devices sharing the same interrupt. Sharing an edge-triggered, ISA interrupt among two or more serial cards can be done if you have a little knowledge of electricity, a few $0.50 parts, and a steady hand with a soldering iron. If anyone wants to understand the electrical details of how and why it works, I will write it up and post it. It will take a couple of hours to write, so I won't bother unless someone is interested in knowing more about it. John
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