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Slave machine not receiving all flight data

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Slave machine not receiving all flight data

Postby aprecelton » Wed Oct 11, 2017 9:16 pm

Hi
I have managed to network 2 computers together in an effort to get one showing the out-the-window view (with the stronger graphics card and processor) and a weaker slave to show the instrument panel. The aircraft in question is the Douglas DC3. They interact ok during flight, but I noticed not all the instruments are working on the slave, such as airspeed indicator, fuel pressure etc. This seems to be the case if it's the graphical aircraft panel, or the 2D panel. The instruments work fine on the master so I suspect it is a data transmission issue over udp.

How do I get the master to transmit all the data to the slave to operate the gauges? I have used the property browser to see if I can identify property values that differ between the 2 machines. But beyond this, I'm lost.

Any suggestions?
Thanks.
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Re: Slave machine not receiving all flight data

Postby wkitty42 » Thu Oct 12, 2017 7:34 pm

remember, UDP transmissions are not guaranteed to make it to the remote once they are on the wire...

the tough way would be to run a network protocol sniffer on both machines and compare the captured traffic... tcpdump and wireshark are two capture tools... wireshark is also used to investigate the PCAPs (traffic captures)... it won't be easy and i don't know of any way to ""diff"" PCAP files to see the differences and find what is missing...
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Re: Slave machine not receiving all flight data

Postby stuart » Fri Oct 13, 2017 9:44 am

Hi,

I think you're looking in the right direction. It's highly likely that the master computer isn't transmitting the properties that are required for some instruments.

To fix it, you'll need to
- Identify the property being used in the animation of the specific instrument that isn't working. Have a look in the instrument .xml files.
- Modify the protocol transmitted by the master to include those properties. You don't say which protocol you're using, but from memory there is an XML definition in the Protocols/ directory.

I don't think the problem is UDP itself, though it's possible that you might be hitting packet size limits

-Stuart
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Re: Slave machine not receiving all flight data

Postby aprecelton » Fri Oct 13, 2017 7:50 pm

Thanks both for your replies.

Stuart, what limits the udp? If the update frequency is changed from 60 to 30hz, can you transmit more data, or can you use a different port! (I sounded like I knew what I was on about then, didn't I?!)

Thanks again, Adam
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Re: Slave machine not receiving all flight data

Postby stuart » Fri Oct 13, 2017 8:32 pm

Hi Adam,

There is a networking limits on the size of UDP packets - basically the maximum size of the IP packet that is transporting it. I just had a quick search, and the max payload size is 65507 Bytes. It's very unlikely you're sending anything like that amount, as most properties are integers or floating point numbers, rather than text.

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