[Paparazzi-devel] Running configuration checked by the server

[Pascal Brisset]

Hi,

Let' start with a true story: last year in Agra, India (MAV08), we 
failed to fly the second aircraft (fortunately the first one flew longer 
than expected). Jeremy launched it in AUTO1, switched to AUTO2 and the 
plane was circling above us; I was able to see it on the GCS and tried 
to switch it to another block. It did not work. I tried several times 
and did not understand what was happening. The first aircraft was still 
flying, Murat, looking at the video was trying to identify obstacles in 
front of the ground vehicle, Michel was planning the next move, asking 
for moving waypoints and changing blocks. They both were asking for 
lower or higher altitude, different angles for the camera... Time was 
running. Jeremy was asking about the second aircraft. He finally landed 
it and rebooted it. And still, I was not able to send anything to it or 
I was not able to understand the effects of the commands.
After 32 minutes, we had to stop and land this brave first Slicer.

Later (the day after ?), we realized that the configuration on the GCS 
for the second aircraft had not been uploaded: a wrong flight plan and 
wrong settings were displayed on the screen !

The server has now been updated to check that the compiled configuration 
on the ground station is the one which has been uploaded to the running 
aircraft. In case of mismatch, no messages will be synthesized by the 
server and the GCS won't be populated. An error message is also sent on 
the paparazzi center console.
This check can be disabled with the -no_md5_check option of the server.

So you will have to recompile your aircraft after your next svn update.

In the next step, of course, the aircraft will have to send its own full 
configuration to the ground station
then allowing any virginal GCS to display correct data

--Pascal

PS: Technical details: A MD5 digest is computed from the configuration 
(airframe, settings, flight plan, ...) and stored in the generated 
airframe.h file (MD5SUM macro) and in the var/AC/conf/aircraft.md5 file. 
This signature is periodically sent in the ALIVE message and the server 
checks the matching of the received value with the one in 
var/AC/conf/aircraft.md5
PSS: Yes, we know that MD5 is far from being perfect. I offer a beer to 
the one able to write two different configurations having the same digest