Re: Modem changes behavior after Sarge Update
Hal Vaughan wrote:
[snip]
Now whenever a program ends, or if I kill a program (so it doesn't have time
to exit), I can tell by watching the modem that it hangs up immediately (the
carrier detect led goes off instantly, along with the clear-to-send light).
I'd think this was a Perl problem, since my programs are in Perl, but it
can't be a reset routine, since I lose the connection even if I kill the
program, without it being able to go through closing down.
This type of behavior is usually caused by "dropping DTR".
I do not have a detailed knowledge of serial interfaces, but my best guess is
that a setting was changed on the serial port or there is something different
in the newer kernel in device drivers. Any help in figuring out what I need
to check in serial port settings or device drivers would be extremely
helpful. (The modem does not use a special driver.)
There are handshake signals used in the RS232. The Data Terminal
Equipment (DTE) (in this case, your computer) signals that it is ready
by asserting Data Terminal Ready (DTR). The Data Communications
Equipment (DCE) signals it is ready by asserting Data Set Ready
(DSR). When the DTE wants to send something, it asserts Request
To Send (RTS). When the DCE is then ready to transmit, it asserts
Clear To Send (CTS). Most modems are configured so that if DTR
is deasserted, they go back on-hook. If your modem displays DTR,
you can check to see whether it is being "dropped".
You might find this http://www.arcelect.com/rs232.htm helpful.
[snip]
Today, the modem can dial and function, EXCEPT whenever the program using it
ends or is killed, the modem drops its connection. I have no idea why, so
any help is appreciated. What could be changed that could force the modem to
hang up whenever the controlling program is killed?
The first step is to find out why the modem is dropping carrier
and going on-hook. Either:
(1) the modem was ignoring DTR before, but has
been reconfigured, possibly by the driver
(2) something changed on your computer so that
DTR is now dropped when it was not before
(3) a change in software (possibly driver) now
commands the modem to go on-hook when the
device is closed
(4) something else I haven't thought of yet
I suggest you look into whether you can configure your modem
not to drop carrier when DTR is dropped. If you can, then
changing this setting may show that it is indeed the cause.
You can just run this way, or get someone who knows more
about configuring serial ports in Debian to help you set it
so that DTR does not get dropped when the port is closed.
If dropping DTR is not the cause, then something else is
happening. You'll have to find out what that is before
you can make progress making it not happen.
Mike
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