Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!pallas!dgl292
From: dgl292@pallas.athenanet.com (Doug Lee)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: HELP NEEDED WITH IBM AT (286) INTERRUPTS!!!
Summary: Send to 20h, also;
Message-ID: <414@pallas.athenanet.com>
Date: 21 Sep 90 18:02:16 GMT
References: <46762.26f56b86@vaxc.cc.monash.edu.au>
Reply-To: dgl292@athenanet.com (Doug Lee)
Lines: 16
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In article <46762.26f56b86@vaxc.cc.monash.edu.au> phs207k@vaxc.cc.monash.edu.au writes:
[about his problems with externally-generated interrupts on an AT...)

You asked if you should send anything to the master interrupt controller
for EOI.  In my experience, for interrupts above IRQ7, it seems to be
necessary to send a 20h to both ports (20h and A0h).  Sending to only one
caused quite an array of bizarre results.

Another caveat (which you may already know):  some BIOSes have the annoying
habit of masking "unusual" interrupts when they are called.  The result is
that, if your routine chains to anything previously hooking that interrupt,
the chain may well reach BIOS, which may stifle any further interrupts.

Hope this helps.

Doug Lee  (dgl292@athenanet.com or uunet!pallas!dgl292)