Comment 26 for bug 1094278

Hmm.
Well we still don't know if the problem is cu or anything else. I doubt it's anything complex with acpi etc.

For perms just do a simple chmod a+rw /dev/ttyS* (as long as you are happy with that and to fix it later and it's a single user system of course!).

OK, 1st question - are you sure you're on the right serial port? Is it really /dev/ttyS0?
If it is,
Then minicom -D /dev/ttyS0

then ctrl-a O and go to serial port setup, check the device, and make sure it's at 115k2 8n1, disable both hardware and software flow control

From the BSD box I'd then do a simple echo hello > /dev/ttyWHATEVER (whatever bsd calls it) and see if the minicom sees it.
If that fials I'd try enabling the getty on the BSD box and see if you see anything on the lInux box.