XN297L@250kbps is emulated by default with the NRF24L01. If option (freq tune) is diffrent from 0, the CC2500 module (if installed) will be used instead with option being the freq usual tuning.
This layer can be enabled/disabled with the option XN297L_CC2500_EMU in _config.h
Protocols which are using it so far:
GD00X, KF606 and MJXQ/E010&PHOENIX