I have seen in the file usrp_basic.h that the minimum value of the gain
is -20 and the maximum is 0. And in the user guide of the USRP, it is
written that the PGA has a maximum gain of 20 dB.
But with Python when you call subdev.gain_range(), the minimum value is
0 and the maximum value is 90. Is it the same? With Python it is just a