Re: Initial state of modems
- From: Aleksander Morgado <aleksander lanedo com>
- To: Dan Williams <dcbw redhat com>
- Cc: Networkmanager List <networkmanager-list gnome org>
- Subject: Re: Initial state of modems
- Date: Tue, 15 Nov 2011 19:33:08 +0100
> > i use a Fasttrack xTend FXT009 with an external power supply.
> > i use MM on an embedded device and the modem is connected over usb.
> > When i have an active connection with the modem, remove the power from
> > the embedded device (so MM has no chance to cleanup anything) and then i
> > restart the embedded device (and MM also restarts), MM can not handle
> > the modem because the modem is still in connection mode.
> > i talked to aleksander on irc and a simple solution is to send "+++"
> > before any other at-command.
> > any problems expected with this solution?
> It depends on the modem. '+++' is one of the ways to break out of
> "data" mode and into "AT" mode, but it's only one of a few. Others
> include dropping DTR for a while or "flashing" the port, and some of
> this depends on the settings you send in the initialization string. One
> question I've got though is if you're removing power from the modem,
> does NM get a port removed signal from udev? That's the expected
> sequence here. If you remove the device, the kernel should notice that,
> send a remove event to MM (through udev) and MM should clean up the
> device anyway. Is that not happening?
The case here is the opposite. ModemManager (or the whole PC) gets
rebooted; while the modem itself is always powered on (and connected).
Therefore, this issue is only applicable to modems with an external
power supply, like the Fastrack and Cinterion/Siemens ones (at least).
If sending '+++' works for this case, we could extend those plugins with
a new custom init command just doing that.
Although it seems to me that the modems should be able to detect that
the link with the DTE is down, and drop the connection automatically in
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