gsmd.

1/ Need to make sure device is working.

   run muxer
   get a connection
   run CFUN? and CFUN=1
   try COPS

   Check if Pin needed.  Watch /var/run/gsm-state/pin to get number.

   If we cannot get anything useful,
        kill muxer
        power down, power up
        try again
        rate limit this severely.

2/ get suspend notification and request updates

   On every update and at least every 30 seconds, get signal strength
      Also check CFUN if 0, try COPS
      validate COPS every 5 minutes
   If COPS? is 0, get COPS=? every 10 minutes. or when
   Store state info in
      /var/run/gsm-state/
           cell  carrier  strength  activity  newsms  incoming signal_strength

3/ When a suspend is signalled
      disable notification of cellid and status - leave SMS
      allow suspend
      on wake, request updates


-------------------------
When sending a command, need to "\r" to get attention
If last reply was more than 5 seconds ago, send 'AT\r' every second
  until get a response, or reset.
Wait for OK, then send command.
Always expect async notifications and handle them directly.

So:
 we need an 'init' string.
  ATV1;E0;+CMEE=2;+CRC=1;

 Then some settings that we can check and set.
  
  +CFUN?   +CFUN: (\d+)   0    +CFUN=1
  +COPS?   +COPS: (.*)    0    +COPS
  +CMFG?   +CMFG: \d      0    +CMGF=1
  +CPIN?   +CPIN: READY
 
 Some things we just periodically get
  +CSQ     +CSQ: \d+,\d+
CLIP
CNMI
CSCB


So each of these settings has:
  - string to send to check
  - string to send to set
  - regexp to see if check or not
  - last send time
  - last recv time
  - count of attempts to set
  - current setting
  - poll timeout
  - handler to call on change


I need to know:
  - phone is on
  - provider
  - cell id
  - signal strength
  - call state
  - incoming caller number
  - incoming TXT message

I need to adjust to requested state:
  - active
  - suspend
  - flight mode

Someone else worries about whether to answer calls etc.

Flight mode must survive power-cycle.  So it doesn't live in /var/volatile.
Probably /var/state or /var/lib/misc

Others are in /var/run places.
There is /var/run/suspend/whatever
and /var/run/gsm/{provider,cell,signal,state,CNI,lasttxt


So states are:
  flight
  suspend
  idle
  incoming
  on-call

For each of these, there is a collection of setting that we want
to impose and monitor