yesterday i managed to show to HUD, the correct RSSI from PIXHAWK analog input (PIN103)
to mini osd.
i searched a lot of forums but no detailed information.
so i used the mini extra OSD Configuration tool (r719).
i solder a cable from the TSLRS Rx to pin 103 on PIXHAWK.
then i made small corrections on mission planner.
RSSI_PIN_HIGH =2 (2 volts max rssi for TSLRS)
RSSI_PIN_LOW =1(1 volts min rssi for TSLRS)
RSSI_TYPE =1(analog input).
hope the above description to help working with TSLRS!