[Paparazzi-devel] ivybus issues

[James Peverill]

I am developing an ivybus application which is designed to display the 
vehicles position (ie read the GPS message).  The software will run on 
another machine (separate IP, running on windows).  I'm having some 
trouble with the Ivybus.  Basically it works, but I only get messages 
from the last IvyBus program that started.  Ie if Datalink was last to 
start, I hear datalink.  If server was last to start, I hear server... 
but not both.

This is easy to see if you run the simulator, and run ivyprobe on your 
local machine you see messages from server and sim.  If you run on 
another machine (with ivyprobe -b <ipaddr> '(.*)'), you see messages 
from only one of them (whichever started most recently).  Starting and 
stopping them in a different order will change which one you can see, 
but still you can hear from only one.

I'm not a networking expert, but it appears that, when a process trying 
to attach to an IvyBus on a different machine, it will only connect with 
the last program that's bound to the port on that machine. In other 
words, the bind() from each program prevents previously running programs 
on that host from seeing the broadcast from the remote program. This is 
consistent with the notion that only one process on the machine can bind 
to a given UDP port at a time.

The interesting thing is multiple programs on the same machine using 
127.0.0.1 (localhost), don't seem to have the same problem - they each 
come up and can see each other program. What am I missing here?

Thanks for your help!


James