AP_Logger: RXLQ in RSSI is in percent

[olliw42]

this is very tiny tidy up: Link quality (LQ) is pretty universally given in units of 0...100%.

[peterbarker]

I'm fine with presenting it that way in the log, but the code that actually fills this packet needs to be updated to x100 the value before logging it (LogFile.cpp ~line 263)

[olliw42]

the code that actually fills this packet needs to be updated to x100 the value before logging it (LogFile.cpp ~line 263)

really? This would explain why the field RXLQ in the log_RSSI is float, but the code has then a bug:

your comment suggests that the intended range for LQ is 0.0 ... 1.0, but the code that fills the packet calls the function rssi->read_receiver_link_quality(), which in turn calls the function RC_Channels::get_receiver_link_quality(), which returns LQ as int16, and moreover the comment says it returns LQ as 0...100 %. RC_Channels::get_receiver_link_quality() in turn calls HAL functions, which are also int16.

• https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_Logger/LogFile.cpp#L253-L267
• https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_RSSI/AP_RSSI.cpp#L161-L168
• https://github.com/ArduPilot/ardupilot/blob/master/libraries/RC_Channel/RC_Channel.h#L474

!?!?

so, if RC_Channels::get_receiver_link_quality() is supposed to return a value in range 0...1, it only would return 0 or 1, and we would have a clear bug. Morever it's in contradiction to the comment.

ergo, the code as is I think is logging 0...100 in %.
If it was supposed to do 0..1 a conversion * 0.01f in rssi->read_receiver_link_quality() is missing, which would have to be undone as you say in the caller.

[peterbarker]

Morever it's in contradiction to the comment

Thanks for delving. I'd prefer 0-1 myself, but it's probably the comment and float return value that needs fixing in the short term. This is all more complicated than it should be, too - I'm trying to move us towards removing RCInput from the HAL entirely, which would eliminate one layer!

[peterbarker]

Merged, thanks!