> How bad are ast and boca boards, how much do they put load on the system ?

Depends on the card, see below.

> The boca board seems to have RJ45 connectors, do they have enough signals 
> to support modems ?

Yes.  RX/TX, RTS/CTS, DSR/DTR, CD, GND.  The only other one you might
want could be RI, but i've never seen anything use that for something
important, and I'd bet that plenty of modems don't even use it.

> Has anyone experimented writing digiboard driver for NetBSD ?

Yeah, I wrote one for the dumb digiboard card.  And boy, do I mean
DUMB.  The dumb digiboard card is a fairly standard arrangement: 8
UARTS on a board, at settable IO addresses, and with interrupt lines
wired together in a system that lets them be shared. It has an 8-bit
status register which provides information on which UART generated an
interrupt. Just like the dumb boca and (I think) ast.

However, while writing and experimenting with the driver, I discovered
how the status register is used. Instead of doing something sensible
like using the 8 bits as flags, one for each UART, they set the status
register to the binary value of the number of the uart that last
interrupted!

This is essentially useless, and you end up having to poll every
(open) UART on each interrupt.

I also discovered a hardware fault with my particular board that broke
some of the ports, and i ended up scavenging it for parts.  I think I
still have the driver lying around, if you do want it let me know.

Digiboard also make a `smart' multiserial card, like any number of
other brands these have some shared memory and a host cpu on the card
to offload a lot of the work. Programming information for these things
is only available under NDA, if at all, for all manufacturers I've
come across.

> There seems to be Linux driver that one could use as a hw-docs,
> would it catch the gnu-public virus that way ?  

Depends.. I'd leave that determination up to your friendly
neighbourhood core team member.

For a dumb card, go with a boca. If you've got the money, consider a
terminal server.

--
Dan.