Currently the USRP device's TX_Control and RX_Control port implementations return only the DDC frequency on the FPGA and do not account for the local oscillator frequency of the daughter boards.
I propose we add the following pure virtual method to the db_base class to allow public access to the LO frequency:
class db_base {
public:
virtual void get_db_freq(float &freq) = 0;
};
Of course this means that all classes which inherit from db_base will need to implement this method.
Most likely this will be implemented by storing the actual frequency in a private member variable when the set_db_freq() method is invoked, but if the daughter board supports it, the get_db_freq() method should query the registers and try to read the value directly from the hardware.
