FlightAware Discussions

Raspberry Pi Capacity

Using PiAware with FlightAware Pro Stick Plus, and FlightAware Filter. I’ve improved my antenna situation and added an external preamp. I’m now tracking over 200 planes during peak times, and over 500 msgs/second. Now I’m seeing CPU approaching 100%. And seem to be having trouble uploading the data to FlightAware. I’m thinking I have just run out of CPU capacity. Any idea which Raspberry Pi I need to go to in order to handle this level of activity? Anyone have real numbers on what the different verisions will handle?

Elvin,
Which RPI are you using now?
I have been running all RPI4s for a year or too. You could easily do it with the 2GB version.

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I used to get a maximum of around 1800 msgs/s and somewhere around 250 aircraft when I was using an rtl dongle on a pi 2 and that was only using 30-40% cpu. When I switched to a pi 4 with the same dongle it didn’t go above ~15% cpu. With an airspy running at 20Mhz the pi 4 can handle over 400 aircraft and 3000+ msgs/s no problem. In fact, the number of aircraft and messages doesn’t really affect the cpu usage all that much.

The current version of dump1090 uses a bit more cpu, but should still be well within the capability of anything other than the first pi or pi zero.

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Sorry, I failed to say that I’m using the PiZeroW.

Thanks for those numbers, caius. Appreciate it. Guess I will do an upgrade…

You can probably barely do it with the zero.
But it would require changing the software around a bit.
obj is working on adding options to dump1090-fa to optionally reduce the CPU used.
But with the piaware sd-card you can’t even manually change the dump1090-fa config … and i don’t know how to disable that.

As such if you want to try with this hardware i’d recommend trying that with a spare sd-card:
Raspbian Lite: ADS B receiver · wiedehopf/adsb-wiki Wiki · GitHub
Use readsb instead of dump1090-fa, i’ve built in automatic detection for systems with only one core (usually pizero) so the demodulation is a bit less CPU hungry (loses maybe 5% of messages or so for a significant reduction in CPU).
Then the gain should be reduced until you start losing a bit of range, that will further reduce CPU usage.

But CPU will still be limited and you’ll probably be limited in regards what extra software you can install. That includes statistics stuff and additional feed clients.
Still thought i’d mention it if you want to give it a try, pretty certain you could get by with the zero with these changes.

Plan is to autodetect slow Pis and turn on options as needed; I’ll probably add an explicit config option too.

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Thanks for the additional information guys. As info, I am not running any additional software on the Pi Zero, and it seemed to work fine up until I hit over 200 planes. At 250, if went totally nuts!

It would be nice to have a table showing an estimate of how many planes each level of Pi’s could handle, but maybe they are cheap enough now that it is best to just throw a Pi4 at it, which is what I will do next.

I don’t know what it is about it being so entertaining to try to keep tweaking and improving the reception, but it sure has been fun tweaking all the pieces of the system. The. Pi is the only component I have not already upgraded. I think this will probably get me to the best I can do in my HOA neighborhood, though I am still considering hiding the antenna inside a vent pipe on the roof. Currently, the antenna is in the attic, just below the peak of the roof.

Thanks again for the help, and thanks to FlightAware for the cool hardware and software!

CPU load tends to be affected more by local RF noise than by message rate / number of aircraft (essentially, a lot of the CPU goes on processing false-positive preambles; only a small fraction of detected “preambles” actually result in a real message) so it’s hard to put a general number on this.

(In fact this caught me out in my testing here - my local RF environment is not particularly noisy so in my testing of 5.0, the ZeroW would easily keep up - but with the wider release we’re seeing installations that are taking a lot more CPU than my test systems)

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Just an update. Switched to a Pi4 and now getting over 200 planes, 575 messages/sec, and 8% CPU. Looks like the Pi4 was overkill, but at least it is stable and not throwing errors now.

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