Article View: comp.sys.ibm.pc.programmer
Article #1438Using IRQ 2 on an AT is tricky
From: Russ Nelson
Date: Sat, 03 Mar 1990 04:44
Date: Sat, 03 Mar 1990 04:44
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I'll bet that you already know that IRQ 2 on the AT bus is mapped to IRQ 9 on the slave 8259. You may even realize that the IRQ 9 handler simply issues an EOI to the slave controller and calls the interrupt associated with IRQ 2 (INT A). This ensures that software written for the PC will work when you use it with IRQ 2. But what I'll bet you *didn't* realize was that IRQ 9 is enabled at boot time. If you have a piece of hardware that generates a spurious IRQ 9 at initialization time, it will get handled by the default IRQ 2 handler. This interrupt handler may not do anything useful. In my case it crashed my machine. My solution is to disable interrupts during the time that I'm initializing the board. -- --russ (nelson@clutx [.bitnet | .clarkson.edu]) Russ.Nelson@$315.268.6667 Violence never solves problems, it just changes them into more subtle problems
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arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!rpi!image.soe.clarkson.edu!newsShow Full Headers
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!rpi!image.soe.clarkson.edu!news From: nelson@sun.soe.clarkson.edu (Russ Nelson) Newsgroups: comp.sys.ibm.pc.programmer Subject: Using IRQ 2 on an AT is tricky Message-ID: <NELSON.90Mar2234357@image.clarkson.edu> Date: 3 Mar 90 04:44:05 GMT Sender: news@sun.soe.clarkson.edu Reply-To: nelson@clutx.clarkson.edu Organization: Clarkson University, Potsdam NY Lines: 18