Date: Sat, 02 Mar 2002 07:20:48 From: "neil barnes" <[EMAIL PROTECTED]> Subject: Re: [LIB]20GB install experience..
>Date: Fri, 01 Mar 2002 14:45:35 -0500 >From: Pres Waterman <[EMAIL PROTECTED]> >Subject: Re: [LIB]20GB install experience.. > > >Gee, I have never heard of an IRQ higher than 15... > Pres, I'm doing this from memory - it's been a long time since I programmed the interrupt system and the text books are in the attic :) There are 256 IRQs available on the x86 chip - or at least 256 spaces in the vector table. The 0-15 limit occurs because the original XT used an interrupt priority controller with eight inputs to control the single IRQ input to the processor, and the AT added another of these chips to give sixteen (really fifteen, as the output of the second chip has to go through the first chip (actually, I think they maybe did that the other way round!)). Those fifteen inputs are available as physical wires on the AT bus, so things that use the AT bus used to have either jumpers or a software routine to set the interrupt number. On the PCI bus, there's a single interrupt connection that everybody sits across and when an interrupt occurs, the device involved sticks a code on the data bus that says, hey, this is me, pay attention. Arbitration happens depending IIRC on position in the bus - which is why sometimes changing the slots around could make things work. Most things on the PCI bus use similar numbers to the same components on the AT bus, but there's no reason why they have to. Plug and pray can allocate them where it wants. I'd guess that the majority of the component blocks on the lib - almost certainly on the later libs - are actually connected on an internal PCI bus (if for no other reason than that it's faster than the AT bus), and that's why interrupt 24 is popping up. Neil _________________________________________________________________ Join the world’s largest e-mail service with MSN Hotmail. http://www.hotmail.com ************************************************************** http://libretto.basiclink.com - Libretto mailing list http://libretto.basiclink.com/archive - Archives http://www.picante.com/~gtaylor/portable/faq.html - FAQ -------TO UNSUBSCRIBE------- Reply to any of the list messages. The reply mail should be addressed to: [EMAIL PROTECTED] - Then replace any text on the message's subject line: cmd:unsubscribe --------TO UNSUBSCRIBE DIGEST------ Do above but with this on subject line: cmd:unsubscribe digest **************************************************************
