Re: [ProgSoc] Sharing interupts in NT

[Telford Tendys <telford@nospam.progsoc.uts.edu.au>]

> > Has anyone got interupt sharing to work on NT? I'm trying to run 6
> > serial ports simultaneously [don't ask why ;-) ] manual says that it
> > can be done. Any ideas ?
> > Geoff
> 
> Theoretically allmost anything can be done.  However.... recently I tried
> to install 2 extra serial ports in an NT machine at work and had nothing
> but trouble.  When I started asking around everyone I asked told me I
> would have trouble.

To the best of my knowledge interrupt sharing isn't possible with AT bus
hardware thanks to the stupidity of the original IBM design all that time
ago. I have tried AT bus cards under Linux and it will accept several
serial ports using the same interrupt but if they are on different cards
then you can only activate one at a time (you can get `four-port' cards
where all the serial ports are on a single card and the sharing logic is
also built onto the card, this does work under Linux because from the
point of view of the AT bus, the interrupt line is still only being used
by a single card).

Frankly, if it doesn't go under Linux, don't bother trying under NT <grin>.

OK, that's AT bus. Most serial ports these days are built into the motherboard
which is slightly different to AT bus but which still can't share with an
AT bus card. Now PCI bus should be OK to share interrupts but in practice you
are limited because you don't see too many PCI serial port cards (other than
the really major ones that have 20 or more ports and cost heaps, even they are
going out of fashion).

> depending on what it is for you might be better off to go buy something
> like a digiboard.  You can get 8 port digiboards with cable (the ones that
> have onboard risc processor) for about $1500 (i think)  and they
> practically set themselves up.

There are quite a few types of serial port cards, ``stallion'' is another
one that comes to mind. Dunno which is the best.

> In addition to that if you are short on free IRQ's in your computer you
> can install a digiboard which will use one IRQ and disable the on board
> serial ports freeing IRQ's 3 and 4.

At the price you quoted above, it is cheaper to buy a whole computer,
a pair of ethernet cards and some cable -- giving you a dedicated machine
just to run two serial ports. Actually, if you are willing to go for
cleaning up some old 486 machines (at about $200 each for just the main
box, allow $20 for ethernet stuff per machine) you can buy 6 machines and
get 12 ports (not counting ports on the main machine which are disabled)
at the price of one ethernet interrupt.

Note that I didn't budget any cost for the operating system software :-)

Your power bill is likely to be high though.

	- Tel
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