You might find the following helps:
For MCU AGC testing, there is an option (checkbox) labeled 'Enable MCU
AGC ’ in LimeSuiteGUI ‘TRX Gain tab’.
From code it can be started/stopped using LMS7_Device::MCU_AGCStart()
and LMS7_Device::MCU_AGCStart() functions:
The code that is executed when toggling ‘Enable AGC’ checkbox in
LimeSuiteGUI can be found here:
LMS chip settings can not be changed while MCU AGC is running, so MCU
AGC should probably be started after finishing configuring the chip.