Recently, somewhere between 1.2 and -current, my 3/60 has lost the ability
to use a modem.  Here's the symptoms:

1.  pppd *nearly* works.  "chat" runs fine, but when pppd tries to take
over, the modem is hung up, and it fails.
2.  cu doesn't work at all.  I can connect to the port, but the first
character I try to send produces, from 'cu -d ...',
cu: fconn_write: Writing 1 "\r"
cu: write: Input/output error

3.  cu works fine to anything but this modem, even other things if I hook
them to this port.
4.  stty -a < /dev/ttyb fails if the modem is on, but works if the modem is
off.
5.  (This is the worst part.)  The same modem, same settings and all, is
working *perfectly* on my Amiga 3000.

I am unable to find anything.  ktrace reveals that write is returning
ENXIO.  Assuming this is from zs8530tty.c, that would mean either
>        if (unit >= zstty_cd.cd_ndevs)
or
>        if (zst == NULL)

However, neither of these seems plausible, given that ttyb works fine with
other devices.

The modem *does* use hardware flow control; is this likely to be a problem?
If so, what kind of problem?  Do I set the modem to not use hardware flow
control, then set it somewhere in the chat, or later on?  I don't get it!

(BTW, "conf.c" says it's talking to a "zs8350".  I assume this is just a
typo, no?)

-s