Date: Sat, 20 Jul 1996 21:48:28 +1000 From: Bruce Evans <bde@zeta.org.au> To: Brett_Glass@ccgate.infoworld.com, alex@fa.tdktca.com Cc: E00114@vnet.atea.be, bde@zeta.org.au, freebsd-hardware@freebsd.org Subject: Re: Multiple COM ports with same IRQ Message-ID: <199607201148.VAA29911@godzilla.zeta.org.au>
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>> Only EISA devices or E-ISA devices can share IRQs. >I think you misunderstand (and why wouldn't you now that you've removed >the context of my message :). The original poster wrote: > ISA boxes can have hardware installed (accidentally?) with devices > sharing the same IRQ, but the drivers cannot deal with it. >I responded with a spiel about IRQ sharing with an ISA bus being an >electrical constraint, not a driver constraint. Bruce responded with... > That's why he only wanted to share them for EISA/ISA boxes :-). >Now help me out if I just don't get this, but the text I had quoted >was about ISA, my followup was about ISA, and then I was corrected(?) >because the original poster wanted to use EISA/ISA boxes (yet I was not >discussing EISA at all). I didn't understand why it was relevant >that the sharing was being done on an EISA/ISA box. IIRC, the original poster only wanted to know about EISA systems with ISA devices and the question was to what exent EISA compensated for the shortcomings of ISA devices. I think it can easily arrange for level triggered IRQs for xx(x)50 devices because the devices naturally produce such IRQs, but it can't make shared IRQs work because it is subject to the same electrical constraints as ISA. Bruce
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