add if gain setter API for rtl-sdr

and OsmoSDR devices

Observations lead to an useful gain
range from 15 to 30dB, a value of
24dB is used by default.

2 files changed, 36 insertions, 27 deletions

diff --git a/lib/osmosdr/osmosdr_src_c.cc b/lib/osmosdr/osmosdr_src_c.cc
index bba0550..68c4a27 100644
--- a/lib/osmosdr/osmosdr_src_c.cc
+++ b/lib/osmosdr/osmosdr_src_c.cc
@@ -131,6 +131,8 @@ osmosdr_src_c::osmosdr_src_c (const std::string &args)
   if (ret < 0)
     throw std::runtime_error("Failed to reset usb buffers.");
 
+  set_if_gain( 24 ); /* preset to a reasonable default (non-GRC use case) */
+
   _buf = (unsigned short **) malloc(_buf_num * sizeof(unsigned short *));
 
   for(unsigned int i = 0; i < _buf_num; ++i)
@@ -410,6 +412,34 @@ bool osmosdr_src_c::get_gain_mode( size_t chan )
 double osmosdr_src_c::set_gain( double gain, size_t chan )
 {
   osmosdr::gain_range_t rf_gains = osmosdr_src_c::get_gain_range( chan );
+
+  if (_dev) {
+    osmosdr_set_tuner_gain( _dev, int(rf_gains.clip(gain) * 10.0) );
+  }
+
+  return get_gain( chan );
+}
+
+double osmosdr_src_c::set_gain( double gain, const std::string & name, size_t chan)
+{
+  return set_gain( gain, chan );
+}
+
+double osmosdr_src_c::get_gain( size_t chan )
+{
+  if ( _dev )
+    return ((double)osmosdr_get_tuner_gain( _dev )) / 10.0;
+
+  return 0;
+}
+
+double osmosdr_src_c::get_gain( const std::string & name, size_t chan )
+{
+  return get_gain( chan );
+}
+
+double osmosdr_src_c::set_if_gain(double gain, size_t chan)
+{
   std::vector< osmosdr::gain_range_t > if_gains;
 
   if_gains += osmosdr::gain_range_t(-3, 6, 9);
@@ -419,9 +449,6 @@ double osmosdr_src_c::set_gain( double gain, size_t chan )
   if_gains += osmosdr::gain_range_t(3, 15, 3);
   if_gains += osmosdr::gain_range_t(3, 15, 3);
 
-  double rf_gain = rf_gains.clip(gain);
-  double missing_gain = gain - rf_gain;
-
   std::map< int, double > gains;
 
   /* initialize with min gains */
@@ -432,7 +459,7 @@ double osmosdr_src_c::set_gain( double gain, size_t chan )
   for (int i = if_gains.size() - 1; i >= 0; i--) {
     osmosdr::gain_range_t range = if_gains[ i ];
 
-    double error = missing_gain;
+    double error = gain;
 
     for( double g = range.start(); g <= range.stop(); g += range.step() ) {
 
@@ -444,7 +471,7 @@ double osmosdr_src_c::set_gain( double gain, size_t chan )
           sum += gains[ j + 1 ];
       }
 
-      double err = abs(missing_gain - sum);
+      double err = abs(gain - sum);
       if (err < error) {
         error = err;
         gains[ i + 1 ] = g;
@@ -452,7 +479,7 @@ double osmosdr_src_c::set_gain( double gain, size_t chan )
     }
   }
 #if 0
-  std::cerr << missing_gain << " => "; double sum = 0;
+  std::cerr << gain << " => "; double sum = 0;
   for (unsigned int i = 0; i < gains.size(); i++) {
     sum += gains[ i + 1 ];
     std::cerr << gains[ i + 1 ] << " ";
@@ -460,32 +487,12 @@ double osmosdr_src_c::set_gain( double gain, size_t chan )
   std::cerr << " = " << sum << std::endl;
 #endif
   if (_dev) {
-    osmosdr_set_tuner_gain( _dev, int(rf_gain * 10.0) );
-
     for (unsigned int stage = 1; stage <= gains.size(); stage++) {
       osmosdr_set_tuner_if_gain( _dev, stage, int(gains[ stage ] * 10.0));
     }
   }
 
-  return get_gain( chan );
-}
-
-double osmosdr_src_c::set_gain( double gain, const std::string & name, size_t chan)
-{
-  return set_gain( gain, chan );
-}
-
-double osmosdr_src_c::get_gain( size_t chan )
-{
-  if ( _dev )
-    return ((double)osmosdr_get_tuner_gain( _dev )) / 10.0;
-
-  return 0;
-}
-
-double osmosdr_src_c::get_gain( const std::string & name, size_t chan )
-{
-  return get_gain( chan );
+  return gain;
 }
 
 std::vector< std::string > osmosdr_src_c::get_antennas( size_t chan )
diff --git a/lib/osmosdr/osmosdr_src_c.h b/lib/osmosdr/osmosdr_src_c.h
index 227ccae..9156454 100644
--- a/lib/osmosdr/osmosdr_src_c.h
+++ b/lib/osmosdr/osmosdr_src_c.h
@@ -105,6 +105,8 @@ private:
   double get_gain( size_t chan = 0 );
   double get_gain( const std::string & name, size_t chan = 0 );
 
+  double set_if_gain( double gain, size_t chan = 0 );
+
   std::vector< std::string > get_antennas( size_t chan = 0 );
   std::string set_antenna( const std::string & antenna, size_t chan = 0 );
   std::string get_antenna( size_t chan = 0 );