JT9889 said:
Can anybody tell me how to read the chart that's in the Asus K8N manual
listing what PCI slots (IRQ assignments) are shared? I can't figure out
what the "INT A" or "INT B" or "INT C" running across the top of the
chart stands for. This is my first attempt at building myself a pc.
The Southbridge on a chipset, traditionally has a number of
interrupt signals on it. For example, an ICH5 has eight interrupt
signals PIRQ_A through PIRQ_H. The Asus manual for a P4C800-E shows
eight columns in the table, labelled A through H.
Thus, each column in the manual, corresponds to one physical
interrupt signal terminated on the Southbridge.
Now, if we look in your manual, we see that PCI slot 1 and PCI
slot 5 are both connected to "INT A". That means those two slots
"share" the same interrupt signal. If you had a card type that
did not like sharing, then stuffing two cards in slot 1 and
slot 5, where one of the cards "hated sharing" would be a
bad thing to do.
When two cards share a physical interrupt signal, the
IRQ number for them must be the same. That is one way
that a user can verify whether the Asus table in the
manual is accurate or not.
OK. Now the first thing you should be aware of, is a
PCI slot actually has four interrupt pins on it. Simple
PCI cards, having only one chip, might only use what
the PCI standard calls the "INTA" signal (not to be
confused with "INT A" in your manual, which happens
to be a signal on the Southbridge).
More complicated PCI cards use two or more of the
signals. (Even an AGP card can use more than one INTx
signal.) In fact, the Asus table is only showing how
the INTA signal is wired on each PCI slot. It is not
showing how INTB, INTC, and INTD are wired. If you use
some utility to examine the IRQ numbers, this might cause
confusion, as the sharing may not appear to match the
manual.
Now that I've got you really confused, what is the poor
user to do ? If you have a sound card that you suspect
does not like to share, plug it into a PCI slot marked
as "used". For example, on your motherboard, PCI slot 4
has the signal "INT D" on the Southbridge, all to itself.
Now, find some tool that shows the IRQ numbers, and see
if the sound card is sharing an IRQ number with other
hardware. If it isn't sharing, you are good to go. If
it is sharing, then perhaps the Asus table is
inaccurate (or it has something to do with the missing
75% of the wiring). In that case, I see that PCI slot 1
and PCI slot 5 are shared with one another, so if you
put the sound card in slot 1 and don't use slot 5, then
you know the card will get its own private interrupt
signal. Use a tool to again check the IRQ numbers for
the hardware. Perhaps this time you'll get lucky.
This is not supposed to matter any more, but if you
had an older Creative sound card, the card may behave
better if it gets to use one interrupt signal for
private use.
Note that, in terms of the IRQ table in the manual,
an Asus desktop manual lists the Southbridge interrupt
signals in the columns. That is why there are eight
columns, corrsponding to the signals on the Southbridge.
The signal wiring is only shown for the first of four
signals on each PCI slot (signal "INTA" on each slot),
so three more tables for the auxiliary three interrupt
pins on a PCI slot are not shown. On an Asus server manual,
the columns in the table correspond to the four interrupt
pins on each PCI slot. Thus, the server table shows the
whole wiring pattern. This is done, because Asus believes
server users use the more complicated, multi-chip PCI
cards that use more than one interrupt pin in the PCI
slot. Also, some server products sport overkill in the
interrupt department, as there can be unique interrupt
signals for each and every pin on the board including
all four interrupt pins in a PCI slot. Such server products
guarantee no conflicts, at least at the physical level.
To see a picture of how interrupts are wired on a
motherboard, there is a tiny picture here:
http://www.fccps.sk/detail.asp?A=0&ID=438
This figure:
http://www.fccps.cz/cz/prod/adv/aktuality/sbernice/obr3.jpg
shows four dots on each PCI slot. Those four dots are the
four interrupt pins. In their example, four interrupt signals
INTA-INTD are wired in what is called a "swizzle pattern". That
pattern kinda evens the load on each signal. The Asus desktop
motherboard manual is only showing how the top "dot" on each
PCI card slot is wired. If we added a fifth PCI slot to this
diagram, then you'd see that PCI slot 1 and PCI slot 5 would
be sharing INTA. Only the Asus server motherboard manuals
document how all the dots are wired.
HTH,
Paul
