Re: [aclug-L] Modem configuration question

[Brian J Chapman <bchapman@xxxxxxxxx>]

okay, i checked my hardware reference so if anyone cares here's the real
story (what me sleep?):

back in the dinosaur days of the PC/XT there was a chip called the 8259A. 
The XT (and the 8259A) only had 8 interrupts. But when along came the AT
specification, they included a second 8259 giving an additional 7 IRQs. 7
because to connect the second interrupt controller they disconnected IRQ 2
from the bus on the first chip and had it receive the output of IRQ 9.
Thus 2 == 9.

My book also states that the AT design has always had provisions for
interrupt sharing but it's use was left up to hardware manufactures and
programmers. hmm...i wonder why no one implemented it?


+------------------------------------------------------------------+
 Brian James Chapman | bchapman@xxxxxxxxx | www.feist.com/~bchapman
+------------------------------------------------------------------+
  "Absolutely nothing should be concluded from these figures except
   that no conclusion can be drawn from them."
                         -- Joseph Brothers, Linux/PowerPC Project


On Thu, 15 Oct 1998, Brian J Chapman wrote:

> The PC architecture was designed in the Dark Ages and has plagued mankind
> ever since. IRQ 9 _IS_ IRQ 2, i forget the technical reason at the moment
> but basicaly just think of 9 as a mirror to 2 and never set anything on
> it otherwise strange happenings may abound.


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