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From: veit@mururoa.gmd.de (Holger Veit)
Subject: Re: Putting a com port at IRQ2
Message-ID: <1993Jul6.124149.14006@gmd.de>
Keywords: com port
Sender: veit@mururoa (Holger Veit)
Nntp-Posting-Host: mururoa
Organization: GMD - German National Research Center for Computer Science
References: <raboczi.741938267@s1.elec.uq.oz.au>
Date: Tue, 6 Jul 1993 12:41:49 GMT
Lines: 32
In article <raboczi.741938267@s1.elec.uq.oz.au>, raboczi@s1.elec.uq.oz.au (Simon Raboczi) writes:
|> I have a four port serial board with 3 16450 UARTs and a single
|> 16550. The IRQ lines for each are selectable in the range 2-5.
|> Operating the com ports off of lines 3-5 works fine, but IRQ 2
|> has been forcibly moved to IRQ 9, judging from what I see in
|> /sys/i386/isa/icu.h . My kernel has the NFS, ISOFS, ethernet
|> and scsi parts excluded, so I don't think there's anything
|> else using IRQ 2.
|>
|> Q1: Is there a good reason IRQ 2 shouldn't be used?
|>
|> Q2: If not, how can I put a com port at IRQ 2?
I guess your serial line board has an 8bit bus. IRQ 2 is unused
on XT systems, so the board might offer this as a valid interrupt.
On an AT system (including the 386/486-ISA boards) there are two
interrupt controllers. The second one is chained to the first via
interrupt line 2, so this one is actually used to forward
interrupts from the second controller. So IRQ 2 is not a good choice.
IRQ 8 which is the first interrupt line on the second controller
serves as the "no interrupt" signal for the second controller.
So the first available interrupt on the second controller is IRQ 9.
|> ,-_|\ Simon Raboczi (raboczi@s1.elec.uq.oz.au)
--
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