Relationship between LQI and RSSI

[rastapasta]

In the NRF52840 (also interested in 833 and 820) it states that LQI is

When receiving a frame the RSSI (reported as negative dB)
will be measured at three points during the reception. These three values will be sorted and the middle
one selected (median 3) for then to be remapped within the LQI range

under section 6.20.12.7. I'm wondering what the `remap` entails? RSSI can be 0-127 and LQI can be 0-255 so is it just scaling by a factor of 2 where 0 RSSI = 255 LQI?

[Kenneth]

Hello,

I am not able to find the exact implementation in hardware, but after some searching and looking at valus, my understanding is that it's almost this simple. However since the valid RSSI values are from -90dBm to -20dBm (see link below), the scaling from RSSI to LQI is done in this interval (e.g. something like so -90dBm -> 0 and -20dBM -> 255). 
https://infocenter.nordicsemi.com/topic/ps_nrf52840/radio.html#unique_1927333262 

Kenneth