[Canberrauav] notes from today's flight test

Andrew Tridgell tridge at samba.org
Thu Dec 15 08:10:48 EST 2011

>  * update message logger - use last 3 bits of timestamp (super-fine
> resolution, just noise) to identify the data link

I've added this now.

>  * BUG: using the multi-link features, when sending new parameters to
> the plane from the GCS, the state model of each link is not updated
> with the new parameter value (unless parameter explicitly "fetched").

also fixed

>  * BUG: episodic latency (stutters ~3s duration) on one link but not
> the other is causing some grief. May be a buffering issue (where;
> xbee? ubiquity? software blocking?). May need to find and fix
> buffering issue, and also handle message asynchronicity differently.

I've fixed this by detecting a delayed (buffered) link using the usec
attributes of some MAVLink messages. That attribute gives the number of
microseconds since the APM booted. When the ground station receives a
packet with a usec attribute that indicates that it is more than a
second older than the last packet it received on another link, it marks
that linked as 'delayed', and stops processing packets from that link
until it is not delayed any more.

I think the reason we are getting a delayed link is that the ubiquity
modem buffers UDP packets, and when that link is marginal then we see
delayed packets. The logging change to identify which packet came from
which link will allow us to prove this next time it happens. The ground
station will also audibly report "link 1 delayed" and "link 1 OK" when
it happens.

Cheers, Tridge

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