LinuxSA Mailing list archives

  From: Andrew Pullin <andrew@hotspurbgc.com.au>
  To  : Andrew Reid <andrew.reid@plug.cx>
  Date: Sun, 8 Apr 2001 18:19:50 +1000

Re: Modem on ttyS3 problem.

Hi All,
    To answer a few questions. If you set minicom in the
options to look at ttyS3, exit and restart minicom it will
look for a modem on ttyS3 (supposedly). While minicom
usually looks for the device on /dev/modem, these options
override it. Minicom doesn't "see" a modem on ttyS3. wvdial
apparently searches for modems on all serial ports (there
are about 100 in /dev/, but the system only "looks for
modems on the first 4 (ttyS0, ttyS1, ttyS2, and ttyS3)
unless you tell it to look somewhere else.

    As I understand the dialin sequence -

    the modem recognises an incoming call and passes a RING
signal to the serial port.
    mgetty "listens" to the serial port and hears the RING
and sends an autoanswer signal ATA to the modem.
    the modem then answers the incoming call and sends the
initial authenticating to the serial port.
    mgetty then authenticates with this data and initiates
pppd.
    pppd starts up and talks to the dialin machine and
initiates a ppp connection.
    The connection remains open until broken (ie. hang up
etc)
    pppd dies.
    modem resets
    mgetty continues to listen.

    As for inittab, I have just set up dialin 1 and got it
to work. Dialin 2 is virtually identical except for the
serial port ttyS3. As far as I can tell the server is doing
what it is supposed to except that it can't "see" the modem
and so is ignoring it.

    I haven't yet tried a serial mouse on this port, so I
will give it a go, however ttyS2 (dos com 3) works fine as
dialin 1 is working on it. setserial reports that the port
is there and set to the correct speeds etc. There is no
bizarre hardware, just a stock standard setup with 4 serial
ports. 2 ports are on board (/dev/ttyS0 and ttyS1).
/dev/ttyS0 is not being used (yet). 2 ports are on an
expansion board (/dev/ttyS2 and ttyS3). setserial detects
all these ports and the interrupts etc are all correct. Hope
this helps with the diagnosis.
    Cheers!
        Andrew.


----- Original Message -----
From: Andrew Reid <andrew.reid@plug.cx>
To: Andrew Pullin <andrew@hotspurbgc.com.au>
Cc: <linuxsa@linuxsa.org.au>
Sent: Sunday, April 08, 2001 5:52 PM
Subject: Re: Modem on ttyS3 problem.


> On 08 Apr 2001 16:17:33 +1000, Andrew Pullin wrote:
>
> > The problem is that
> > even though setserial advises that the ttyS* ports are
there
> > and configured correctly, and the Linux side of things
are
> > set up (ie mgetty etc. it was almost identical setup to
the
> > dialin 1 config), I cannot 'find' the third modem when I
use
> > any terminal programs like minicom or wvdial.
>
> Minicom generally uses /dev/modem as the modem to try and
talk to. If
> /dev/modem doesn't exist or links to the wrong device, you
may have a
> problem talking to it.
>
> > Also the modem doesn't pick up the incoming call and
pass
> > it on to mgetty.
>
> Well, the sequence is somewhat different to that. If
you've got an
> external modem, you'll notice that when you call the phone
number that
> modem is connected to, a little light flashes. Mgetty
waits for one of
> these flashes, or signals as mgetty reads them, and does
something like
> answer the call with them.
>
> >     I think that the not seeing the 3rd modem is the
problem
> > here, but I don't know what to do to fix it. The modem
> > detects the incoming call (the Ring Indicator light
comes
> > on). I think that because the system cannot see the
modem
> > connected to the port it also isn't picking up the Ring
> > signal from the modem and so isn't firing up mgetty and
> > subsequently pppd.
>
> Is there anything in inittab for mgetty on /dev/ttyS3?
There should be
> if you want it to answer the call. Just a clarification --
mgetty is
> _always_ running in these circumstances. In inittab, the
respawn option
> is generally specified. This means that as soon as one
instance of the
> process (mgetty) dies, another starts.
>
> >     The usual method of checking for a modem is to send
an
> > init string to the port and if it receives an OK signal
> > back, then there is a modem connected to that line. Is
there
> > anything people can suggest to help here? Are there any
> > other methods of checking serial ports for modems? Are
there
> > any other ways to initialise (or send any data) to a
modem?
>
> Can you use other devices on this port? For example, a
serial mouse or
> something similar. One thing I'd ask is, how many physical
serial ports
> does this beast have? /dev/ttyS0-3 means 4 ports. Do you
have any bizare
> hardware inside this machine to give you the phyical
plugs?
>
>    -Andrew
>
> --
> Andrew Reid                   email: andrew.reid@plug.cx
>                               www:   http://www.plug.cx
> "No one gets too old to       phone: +61 401 946 813
>  learn a new way of being
>  stupid."
>

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