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For pull request:
Make LOS/RSSI branch (after weekend)
Research
RSSI signal can come as analog or PWM
Ardupilot implementation
RSSI.cpp calls on AnalopIn.cpp class for its ‘channel’ function
AnalogIn.cpp has ‘channel’ function which returns a pointer to an AnalogSource object by calling the ADCSource object constructor
(ADCSource inherits from AnalogSource)
https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_HAL_SITL/AnalogIn.cpp
AnalogSource is an abstract class, defines in a different AnalogIn file