Date: Fri, 19 Jul 1996 08:45:30 -0700 From: "Michael L. VanLoon -- HeadCandy.com" <michaelv@HeadCandy.com> To: E00114@vnet.atea.be (Rob Schofield) Cc: freebsd-hardware@freebsd.org Subject: Re: Multiple COM ports with same IRQ Message-ID: <199607191545.IAA18234@MindBender.HeadCandy.com> In-Reply-To: Your message of Fri, 19 Jul 96 09:43:10 %2B0700. <vines.mmb7%2BOmnvlA@vnet.atea.be>
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>Additionally, we have the question of the interrupt being Edge (it spikes
>down, which latches on the interrupt controller) or level (it goes down and
>stays down until the CPU has serviced it).
>
>I have an EISA box which allows you to say "for this device at this address,
>expect an interrupt on IRQ X, level triggered" or "edge triggered". This sets
>up the PIC (interrupt controller) to expect a certain type of interrupt
>alright, but if the card in the slot doesn't behave like that, then
>interrupts might not register with the PIC.
>
>The original question was really to fish for opinions - given conventional
>UARTS (16550s) on an ISA card in an EISA box, can I set these two up to
>appear as a multiport by setting up the interrupt controller to handle two
>UARTs at different register addresses but sharing the same IRQ line? (ie.
>"dupe" sio into thinking it's handling a multiport).
I don't think so. If it works, it's by accident.
Edge-triggered interrupts are a specific feature of the EISA design.
ISA cards do not know how to do that. You need an _EISA_ board, in an
EISA bus, to correctly support this.
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Michael L. VanLoon michaelv@HeadCandy.com
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