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Re: Fixed! (Re: mgetty isn't answering the phone (ioctl problem))

On Thu, 24 Oct 1996, Pete Harlan wrote:

> > I use DCON..  its DCON that can't OPEN the port...  pppd works fine, and
> > mgetty work fine.. but its DCON that can't share the port...
> That would happen if DCON is trying to open, say, /dev/cua0, rather
> than /dev/ttyS0.  mgetty will get in the way of that.  The Serial Gods
> could tell you a lot more than I can, but I do know that if everyone
> uses ttyS<n> then everyone is happy.  I don't know what DCON is, but
> perhaps you can reconfigure it.
No, its on /dev/ttyS3, both of them...

> Part of reconfiguring it is to make sure it obeys the locking
> conventions; as far as I know all the cua<n> devices did for you was a
> kernel-level lock, rather than the cooperative, user-space method used
> by programs sharing ttyS<n>.
> Gorier detail: mgetty does a select() on ttyS0, waiting for the modem
> to do something (e.g., emit "RING").  Because mgetty has ttyS0 open,
> trying to open cua0 fails (or blocks, perhaps), which is presumably
> what's happening with DCON.  But you can still open ttyS0, and use it;
> the first time you cause the modem to emit any characters, mgetty's
> select() returns, and if mgetty finds that someone else has written a
> lockfile it quits.  If someone hasn't written a lockfile, then mgetty
> writes the lockfile itself and tries to make sense of what the modem
> is saying (usually "RING", but maybe "AT..." if your program is trying
> to use the modem without having written the lockfile).
> The moral being that your program should open ttyS0, but if it hasn't
> written a lockfile before it talks to the modem, your program and
> mgetty will trip over each other trying to converse with it.

Its DCON thats doing the tripping, is the problem :)

                              Daniel Stringfield  
        mailto:servo@jax-inter.net http://www.jax-inter.net/user/servo
    Send email for more information on the Jacksonville Linux Users Group!

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