> 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 : -) ?
>
finally i did

com0 at isa0 port 0x3f8-0x3ff irq 4: ns16550a, working fifo
com1 at isa0 port 0x2f8-0x2ff irq 3: ns16550a, working fifo
com2 at isa0 port 0x3e8-0x3ef irq 10: ns16550a, working fifo
com3 at isa0 port 0x2e8-0x2ef irq 11: ns16550a, working fifo
lpt0 at isa0 port 0x378-0x37b irq 7
lpt1 at isa0 port 0x278-0x27b: polled
sb0 at isapnp0 port 0x220/16,0x330/2,0x388/4 irq 5 drq 1,5
fdc0 at isa0 port 0x3f0-0x3f7 irq 6 drq 2
pckbc0: using irq 1 for kbd slot
pckbc0: using irq 12 for aux slot

and ended with every add-on PCI device shares irq 9 as there are no more
left.

is it possible to make IDE channels share irq 14 in BIOS?
they default get 14 and 15