[Discuss-gnuradio] DBSRx set gain code

[Lee Patton]

I don't understand why the gain range returned by the DBSRx ranges from
0 to 104 when the PGA gives only 0 to 20 dB.  Obviously, the answer lies
in db_dbs_rx.py, but I haven't a clue as to what the code is really
doing.  Can anyone (Eric) explain?  I read about Registers 2/3 in the
AD9862 data sheet, but I couldn't correlate that information with the
code.

Also, I found gnuradio-core/doc and usrp/doc. Is there any more code
documentation that I am not aware of?

Thanks,
 - Lee


    181     # Gain setting
    182     def _set_dl(self,dl):
    183         assert dl == 0 or dl == 1
    184         self.dl = dl
    185         self._send_reg(4)
    186
    187     def _set_gc2(self,gc2):
    188         assert gc2<32 and gc2>=0
    189         self.gc2 = gc2
    190         self._send_reg(5)
    191
    192     def _set_gc1(self,gc1):
    193         assert gc1>=0 and gc1<4096
    194         self.gc1 = gc1
    195         self._u.write_aux_dac(self._which,0,int(gc1))
    196
    197     def _set_pga(self, pga_gain):
    198         assert pga_gain >=0 and pga_gain <=20
    199         if(self._which == 0):
    200             self._u.set_pga (0, pga_gain)
    201             self._u.set_pga (1, pga_gain)
    202         else:
    203             self._u.set_pga (2, pga_gain)
    204             self._u.set_pga (3, pga_gain)
    205
    206     def gain_range(self):
    207         return (0, 104, 1)
    208
    209     def set_gain(self,gain):
    210         if not (gain>=0 and gain<105):
    211             raise ValueError, "gain out of range"
    212         gc1 = 0
    213         gc2 = 0
    214         dl = 0
    215         pga = 0
    216         if gain <56:
    217             gc1 = int((-gain*1.85/56 + 2.6)*4096/3.3)
    218             gain = 0
    219         else:
    220             gc1 = 0
    221             gain = gain - 56
    222         if gain < 24:
    223             gc2 = int(round(31 * (1-gain/24)))
    224             gain = 0
    225         else:
    226             gc2 = 0
    227             gain = gain - 24
    228         if gain >= 4.58:
    229             dl = 1
    230             gain = gain - 4.58
    231         pga = gain
    232         print "Gain %f" % pga
    233         self._set_gc1(gc1)
    234         self._set_gc2(gc2)
    235         self._set_dl(dl)
    236         self._set_pga(pga)
    237