Making disconnection more robust

[Tim Small]

Hello,

As previously discussed, the disconnection code currently does no
checking to verify that the modem has come back into command mode (it
just drops DTR for a second, and hopes for the best) i.e.

[Drop DTR]
[end disconnect sequence, assuming modem is back in command mode]




I'd like to change this so that the command flow is:

[Drop DTR]
[send "AT<CR>"]
[proceed if the modem replied with "OK"]

... if "OK" isn't received within the timeout, then:

[report modem still not in command mode]
["+++"]
["wait for end of escape guard interval"]
[end disconnect sequence if the modem replied with "OK", otherwise...]
[send "AT<CR>"]
[end disconnect sequence if the modem replied with "OK", otherwise...]

... if "OK" isn't received within the timeout, then:

[report modem still not in command mode]
[serial "break"]
[end disconnect sequence if the modem replied with "OK", otherwise...]
[report failure to disconnect modem?]



What roughly would a reasonable implementation of the "check AT-OK, if
not then try next method" process look like?  I've been poking about
with src/mm-broadband-bearer.c - but don't really have a clear idea how
to proceed...

I'm assuming that I would use mm_base_modem_at_command_full to send the
"AT<CR>" commands, but is it ok to do this from a command completion
handler?

Are there any existing analogous exchanges which I could take a look at
to base this on?

Cheers,

Tim.

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