Questions about MAVLink package saturation

ArduPlane Plane 4.0
,
1

Cube Black:
Serial 0,1,3,4 are all configured for MAVLink1
at the following rates:

    SR0_ADSB,4
    SR0_EXTRA1,10
    SR0_EXTRA2,10
    SR0_EXTRA3,2
    SR0_EXT_STAT,2
    SR0_PARAMS,10
    SR0_POSITION,3
    SR0_RAW_CTRL,4
    SR0_RAW_SENS,2
    SR0_RC_CHAN,2
    SR1_ADSB,4
    SR1_EXTRA1,10
    SR1_EXTRA2,10
    SR1_EXTRA3,2
    SR1_EXT_STAT,2
    SR1_PARAMS,10
    SR1_POSITION,3
    SR1_RAW_CTRL,4
    SR1_RAW_SENS,2
    SR1_RC_CHAN,2

    SR3_ADSB,0
    SR3_EXTRA1,10
    SR3_EXTRA2,10
    SR3_EXTRA3,2
    SR3_EXT_STAT,2
    SR3_PARAMS,0
    SR3_POSITION,3
    SR3_RAW_CTRL,0
    SR3_RAW_SENS,2
    SR3_RC_CHAN,2

I observe a low VFR_HUD rate (and other rates, barely at 1Hz on the companion computer connected to SR3 , which should have been at 10Hz )

Questions:
SR0 is not connected - does it still load the CPU ? - are the packets generated anyway?

How can I see/know how much of the requested data is actually generated i time ? (and how much is dropped ?) is there any performance-monitoring for this?

What is the logic behind which packets/interfaces are prioritized ?

2

I wrote a pymavlink script to calculate the requested data rate for copter.
It would be very easy to change that script for the plane. It would answer some of your questions.

3

@amilcarlucas Thank you, I am not concerned about the data rate as we have a serious radio onboard, My problem is what the limits of the ArduPilot are, in terms of generating mavlink packets for all the interfaces.
…Unless there is a known limit to that - of course.

I have low datarates on SR3 to onboard computer, but they increase a bit, for a while, if I reduce datarates of SR1 …

4

as far as i use arducopter and arduplane on my projects (i did many, in many years) i often had problems with mavlink rate saturations, randomic slowness etc and i didn’t ever fully grasp why and how it happens. Mainly, it affects the parameter loading phase, which can fail at times.
I tried hope-rf based Sik radios, RF design 900x modules, and others, most of them gave problems, sometime fixed or got worse with “small” config differences, i.e. different FW versions, sik configs, or putting or leaving extra functions i.e. RTK streaming with F9P base antennas make it much worse, adding a frontal rangefinder for avoidance/proximity litterally kills it. “tuning” SR parameters can help, but don’t fix it al all. I think it’s a “structural” flaw of the system.

5

Please note that I am not mentioning RF-transmission, just the observed rates at onboard computer.
I do not suspect a single serial link being saturated, but rather the mavlink generating loop to have spent it’s time slot way before assembling enough packets as requested.