Re: Initial state of modems

[Dan Williams <dcbw redhat com>]

On Tue, 2011-11-15 at 11:13 +0100, Thomas Bechtold wrote:
> Hi,
> 
> 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?

Dan