RSL15 has dedicated hardware designed to handled Bluetooth Low Energy activities and events. From one side, the HW communicates with the RFFE through internal an SPI interface for RX or TX programming and radio FSM control purposes, along with internal signals connected between Bluetooth Low Energy hardware and the RF front-end for the TX/RX data/clock and IQ data. From the other side, the hardware communicates to the Bluetooth Low Energy stack software, executed in firmware through shared memory, Bluetooth Low Energy interrupts, and Bluetooth Low Energy hardware registers.
For more information about this topic, see: