> anyway 8-port ISA card can have every of it's port on one irq and it
> works.
> but it has extra chip to queue ints

If you share two ISA com card on the same irq, NetBSD don't know from which
card the interrupt is and call the two configured driver, while the 8-port
ISA card irqs are holded by an on-board chip and the driver, then could use
one irq.

In my case of ethernets irqs conflict, the 3c509 worked and the ne2000
generated "i/o timeouts..." and won't work. ( kernel saying "last message
repeated 123 times" sometimes... )
I have found that one card is irq level sensitive while the other on edge
transition, may be the why one worked...

I know isa irq sharing could be done by polling the hardware on interrupts
to look at which card triggered, included in drivers or kernel... It would
be a little like PCI irq holder/steering, ..., done in software. I don't
know about compatibles hardwares and NetBSD implementation, possible
conflicts or success in doing this, but aware of it.

You can add more coms but must have a memory adress and an irq for each, in
case of standard pc hardware.
com 1 : 0x3f8, irq 4
com 2 : 0x2f8, irq 3
com 3 : 0x3e8, irq 6 ?
com 4 : 0x2e8, irq 5 ?
com x : -) ?

isn't it ?