How is Bluetooth transmit power determined?

[andyn_ff]

Hi,

I am developing an application using Bluetooth on ESP32, and I see in ESP-IDF it is possible to configure Bluetooth Tx power (I am using BR/EDR mode). However, the ESP-IDF functions take a minimum and maximum power. How is the transmit power determined between this minimum and maximum?

I tried using the ESP-IDF components to understand this, as I cannot find anything relevant in the ESP32 technical reference manual. However, following the calls through into the IDF code, I cannot find any implementation of bredr_txpwr_set(min, max), so I assume this is implemented in ROM and I cannot see it?

Please can you help me understand how the Bluetooth controller determines the transmit power to use at any moment?

Thanks,
Andy