Protocol Definition between Ground Stations and Command RX
==========================================================


Introduction
------------

- using DTMF on FM
- receiver should be activated for min. 200ms every 5s to listen for new commands
- signs get scrambled using a secret Code Table
- every command must be aknowledged by a beacon with the unscrambled code

Frame
-----

#42<code><cs>

Checksum:
---------

XOR over Signs intrepreted as 4-bit numbers (see translation table below)

   DTMF-Sign  |  Number
  ------------+----------
       D      |    0
       1      |    1
       2      |    2
       3      |    3
       4      |    4
       5      |    5
       6      |    6
       7      |    7
       8      |    8
       9      |    9
       0      |   10
       *      |   11
       #      |   12
       A      |   13
       B      |   14
       C      |   15
 

Codes:
------

0    ..    shut up (rfkill)
1    ..    unshut up (no rfkill)

8    ..    activate payload receiver
9    ..    reset settings
C    ..    cancel all commands
#    ..    reset (hardware reboot only)
*    ..    safe mode (stop all activties and harvest energy)