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[Paparazzi-devel] Running configuration checked by the server

From: Pascal Brisset
Subject: [Paparazzi-devel] Running configuration checked by the server
Date: Thu, 02 Apr 2009 00:15:21 +0200
User-agent: Thunderbird (X11/20090318)


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


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

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