🚀 go-pugleaf

In article <rO9ACAAphHe3EwAI@dunvegan1.demon.co.uk>, Paul Richards
<Paul@dunvegan1.demon.co.uk> writes
>
>Tom Bird writes,
>[stuff about IRQ's]
>
>It's amazing how much trouble some ppl have with IRQ's and I've never
>had any problems with them.  I've got 2 ISA cards, 2 PCI cards, 2 COM
>ports (do these take IRQ's?) and 1 LPT port (takes an IRQ?).  How many
>IRQ's do PC's have?  Is there a "map" of IRQ's somewhere that shows you
>what's attached to them?

By default (just a basic machine, EIDE, 2S, 1P)

00 - System Timer
01 - keyboard
02 - cascade for second 8259 [1]
03 - COM 2
04 - COM 1
06 - FDD
07 - LPT 1
08 - system RTC
09 - linked to IRQ2 for the cascade
12 - PS/2 mouse
13 - maths co-pro (not really necessary but that's just tough)
14 - EIDE 1
15 - EIDE 2

[1] XT's only had 8 interrupts, from one 8259 interrupt controller.
When they made the AT (286), they botched the second 8259 (for more
interrupts) onto IRQ 2 for compatibility.  If you have ever tried to get
two conflicting devices onto 2 and 9, it won't work.  They are the same
interrupt.

On my machine, as I have only occasional need for IDE (testing devices),
EIDE 2 is disabled.  Got me back a whole interrupt, that did.  The
Matrox Marvel nicked that one.

>I suppose juggling IRQ's was like the good ol' days of juggling about to
>get 3 Kb more conventional memory...?

Ooarr... my old 286, 640k RAM - to get some of the fancier games to run,
I had to actually execute them from config.sys with the 'install'
command - command.com took too much RAM, I needed about 614k free for
this game.  With no HMA, EMS or XMS to offload data into, it was tight
but it worked.  I had a 1Mb graphics card in that PC, I used to use
Windows 3.0 in real mode, in 1024x768 256 colours.  The frame buffer was
bigger than the total main RAM.

HTH,
TB