hackrf: add TX support (wip)

features:

- gain control for AMP & VGA
- frequency error correction
- automatic baseband filter
- up to 20M sampling rate

limitations:

- no DC offset correction implemented (yet)
- high sampling rates may not work on slow machines

the following TX named gain stages are available:

RF: MGA-81563, switchable 0 or 14dB
IF: MAX2837 VGA, 0 to 47dB in 1dB steps

6 files changed, 1522 insertions, 33 deletions

diff --git a/lib/hackrf/CMakeLists.txt b/lib/hackrf/CMakeLists.txt
index 7eb7076..31f991b 100644
--- a/lib/hackrf/CMakeLists.txt
+++ b/lib/hackrf/CMakeLists.txt
@@ -28,6 +28,7 @@ include_directories(
 
 set(hackrf_srcs
     ${CMAKE_CURRENT_SOURCE_DIR}/hackrf_source_c.cc
+    ${CMAKE_CURRENT_SOURCE_DIR}/hackrf_sink_c.cc
 )
 
 ########################################################################
diff --git a/lib/hackrf/hackrf_sink_c.cc b/lib/hackrf/hackrf_sink_c.cc
index 011000a..58a49cb 100644
--- a/lib/hackrf/hackrf_sink_c.cc
+++ b/lib/hackrf/hackrf_sink_c.cc
@@ -27,15 +27,91 @@
 #include "config.h"
 #endif
 
-#include "hackrf_sink_c.h"
+#include <stdexcept>
+#include <iostream>
+
+#include <boost/assign.hpp>
+#include <boost/format.hpp>
+#include <boost/detail/endian.hpp>
+#include <boost/algorithm/string.hpp>
+
 #include <gnuradio/gr_io_signature.h>
 
-/*
- * Create a new instance of hackrf_sink_c and return
- * a boost shared_ptr.  This is effectively the public constructor.
- */
-hackrf_sink_c_sptr
-make_hackrf_sink_c (const std::string &args)
+#include "hackrf_sink_c.h"
+
+#include "osmosdr_arg_helpers.h"
+
+using namespace boost::assign;
+
+#define BUF_LEN  (16 * 32 * 512) /* must be multiple of 512 */
+#define BUF_NUM   32
+
+#define BYTES_PER_SAMPLE  2 /* HackRF device consumes 8 bit unsigned IQ data */
+
+static inline bool cb_init(circular_buffer_t *cb, size_t capacity, size_t sz)
+{
+  cb->buffer = malloc(capacity * sz);
+  if(cb->buffer == NULL)
+    return false; // handle error
+  cb->buffer_end = (char *)cb->buffer + capacity * sz;
+  cb->capacity = capacity;
+  cb->count = 0;
+  cb->sz = sz;
+  cb->head = cb->buffer;
+  cb->tail = cb->buffer;
+  return true;
+}
+
+static inline void cb_free(circular_buffer_t *cb)
+{
+  if (cb->buffer) {
+    free(cb->buffer);
+    cb->buffer = NULL;
+  }
+  // clear out other fields too, just to be safe
+  cb->buffer_end = 0;
+  cb->capacity = 0;
+  cb->count = 0;
+  cb->sz = 0;
+  cb->head = 0;
+  cb->tail = 0;
+}
+
+static inline bool cb_has_room(circular_buffer_t *cb)
+{
+  if(cb->count == cb->capacity)
+    return false;
+  return true;
+}
+
+static inline bool cb_push_back(circular_buffer_t *cb, const void *item)
+{
+  if(cb->count == cb->capacity)
+    return false; // handle error
+  memcpy(cb->head, item, cb->sz);
+  cb->head = (char *)cb->head + cb->sz;
+  if(cb->head == cb->buffer_end)
+    cb->head = cb->buffer;
+  cb->count++;
+  return true;
+}
+
+static inline bool cb_pop_front(circular_buffer_t *cb, void *item)
+{
+  if(cb->count == 0)
+    return false; // handle error
+  memcpy(item, cb->tail, cb->sz);
+  cb->tail = (char *)cb->tail + cb->sz;
+  if(cb->tail == cb->buffer_end)
+    cb->tail = cb->buffer;
+  cb->count--;
+  return true;
+}
+
+int hackrf_sink_c::_usage = 0;
+boost::mutex hackrf_sink_c::_usage_mutex;
+
+hackrf_sink_c_sptr make_hackrf_sink_c (const std::string & args)
 {
   return gnuradio::get_initial_sptr(new hackrf_sink_c (args));
 }
@@ -47,7 +123,7 @@ make_hackrf_sink_c (const std::string &args)
  * output signatures are used by the runtime system to
  * check that a valid number and type of inputs and outputs
  * are connected to this block.  In this case, we accept
- * only 1 input and 0 output.
+ * only 0 input and 1 output.
  */
 static const int MIN_IN = 1;	// mininum number of input streams
 static const int MAX_IN = 1;	// maximum number of input streams
@@ -60,9 +136,83 @@ static const int MAX_OUT = 0;	// maximum number of output streams
 hackrf_sink_c::hackrf_sink_c (const std::string &args)
   : gr_sync_block ("hackrf_sink_c",
         gr_make_io_signature (MIN_IN, MAX_IN, sizeof (gr_complex)),
-        gr_make_io_signature (MIN_OUT, MAX_OUT, sizeof (gr_complex)))
+        gr_make_io_signature (MIN_OUT, MAX_OUT, sizeof (gr_complex))),
+    _dev(NULL),
+    _buf(NULL),
+    _sample_rate(0),
+    _center_freq(0),
+    _freq_corr(0),
+    _auto_gain(false),
+    _amp_gain(0),
+    _vga_gain(0)
 {
+  int ret;
+  uint16_t val;
+
+  dict_t dict = params_to_dict(args);
+
+  _buf_num = 0;
 
+  if (dict.count("buffers"))
+    _buf_num = boost::lexical_cast< unsigned int >( dict["buffers"] );
+
+  if (0 == _buf_num)
+    _buf_num = BUF_NUM;
+
+  {
+    boost::mutex::scoped_lock lock( _usage_mutex );
+
+    if ( _usage == 0 )
+      hackrf_init(); /* call only once before the first open */
+
+    _usage++;
+  }
+
+  _dev = NULL;
+  ret = hackrf_open( &_dev );
+  if (ret != HACKRF_SUCCESS)
+    throw std::runtime_error("Failed to open HackRF device.");
+
+  uint8_t board_id;
+  ret = hackrf_board_id_read( _dev, &board_id );
+  if (ret != HACKRF_SUCCESS)
+    throw std::runtime_error("Failed to get board id.");
+
+  char version[40];
+  memset(version, 0, sizeof(version));
+  ret = hackrf_version_string_read( _dev, version, sizeof(version));
+  if (ret != HACKRF_SUCCESS)
+    throw std::runtime_error("Failed to read version string.");
+#if 0
+  read_partid_serialno_t serial_number;
+  ret = hackrf_board_partid_serialno_read( _dev, &serial_number );
+  if (ret != HACKRF_SUCCESS)
+    throw std::runtime_error("Failed to read serial number.");
+#endif
+  std::cerr << "Using " << hackrf_board_id_name(hackrf_board_id(board_id)) << " "
+            << "with firmware " << version << " "
+            << std::endl;
+
+  if ( BUF_NUM != _buf_num ) {
+    std::cerr << "Using " << _buf_num << " buffers of size " << BUF_LEN << "."
+              << std::endl;
+  }
+
+  set_sample_rate( 5000000 );
+
+  set_gain( 0 ); /* disable AMP gain stage */
+
+  hackrf_max2837_read( _dev, 29, &val );
+  val |= 0x3; /* enable TX VGA control over SPI */
+  hackrf_max2837_write( _dev, 29, val );
+
+  set_if_gain( 16 ); /* preset to a reasonable default (non-GRC use case) */
+
+  _buf = (unsigned char *) malloc( BUF_LEN );
+
+  cb_init( &_cbuf, _buf_num, BUF_LEN );
+
+//  _thread = gruel::thread(_hackrf_wait, this);
 }
 
 /*
@@ -70,5 +220,503 @@ hackrf_sink_c::hackrf_sink_c (const std::string &args)
  */
 hackrf_sink_c::~hackrf_sink_c ()
 {
+  if (_dev) {
+//    _thread.join();
+    hackrf_close( _dev );
+    _dev = NULL;
+
+    {
+      boost::mutex::scoped_lock lock( _usage_mutex );
+
+       _usage--;
+
+      if ( _usage == 0 )
+        hackrf_exit(); /* call only once after last close */
+    }
+  }
+
+  if (_buf) {
+    free(_buf);
+    _buf = NULL;
+  }
+
+  cb_free( &_cbuf );
+}
+
+int hackrf_sink_c::_hackrf_tx_callback(hackrf_transfer *transfer)
+{
+  hackrf_sink_c *obj = (hackrf_sink_c *)transfer->tx_ctx;
+  return obj->hackrf_tx_callback(transfer->buffer, transfer->valid_length);
+}
+
+int hackrf_sink_c::hackrf_tx_callback(unsigned char *buffer, uint32_t length)
+{
+#if 0
+  for (unsigned int i = 0; i < length; ++i) /* simulate noise */
+    *buffer++ = rand() % 255;
+#else
+  {
+    boost::mutex::scoped_lock lock( _buf_mutex );
+
+    if ( ! cb_pop_front( &_cbuf, buffer ) ) {
+      memset(buffer, 0, length);
+      std::cerr << "U" << std::flush;
+    } else {
+//      std::cerr << ":" << std::flush;
+      _buf_cond.notify_one();
+    }
+  }
+
+#endif
+
+  return 0; // TODO: return -1 on error/stop
+}
+
+void hackrf_sink_c::_hackrf_wait(hackrf_sink_c *obj)
+{
+  obj->hackrf_wait();
+}
+
+void hackrf_sink_c::hackrf_wait()
+{
+}
+
+bool hackrf_sink_c::start()
+{
+  if ( ! _dev )
+    return false;
+
+  _buf_used = 0;
+
+  int ret = hackrf_start_tx( _dev, _hackrf_tx_callback, (void *)this );
+  if (ret != HACKRF_SUCCESS) {
+    std::cerr << "Failed to start TX streaming (" << ret << ")" << std::endl;
+    return false;
+  }
+
+  while ( ! hackrf_is_streaming( _dev ) );
+
+  return (bool) hackrf_is_streaming( _dev );
+}
+
+bool hackrf_sink_c::stop()
+{
+  if ( ! _dev )
+    return false;
+
+  int ret = hackrf_stop_tx( _dev );
+  if (ret != HACKRF_SUCCESS) {
+    std::cerr << "Failed to stop TX streaming (" << ret << ")" << std::endl;
+    return false;
+  }
+
+  while ( hackrf_is_streaming( _dev ) );
+
+  /* FIXME: hackrf_stop_tx should wait until the device is ready for a start */
+  usleep(100000); /* required if we want to immediately start() again */
+
+  return ! (bool) hackrf_is_streaming( _dev );
+}
+
+int hackrf_sink_c::work( int noutput_items,
+                         gr_vector_const_void_star &input_items,
+                         gr_vector_void_star &output_items )
+{
+  const gr_complex *in = (const gr_complex *) input_items[0];
+
+  {
+    boost::mutex::scoped_lock lock( _buf_mutex );
+
+    while ( ! cb_has_room(&_cbuf) )
+      _buf_cond.wait( lock );
+  }
+
+  unsigned char *buf = _buf + _buf_used;
+
+  int items_consumed = 0;
+  unsigned int prev_buf_used = _buf_used;
+
+  for (int i = 0; i < noutput_items; i++) {
+    if ( _buf_used + BYTES_PER_SAMPLE > BUF_LEN ) {
+      {
+        boost::mutex::scoped_lock lock( _buf_mutex );
+
+        if ( ! cb_push_back( &_cbuf, _buf ) ) {
+          _buf_used = prev_buf_used;
+          items_consumed = 0;
+          std::cerr << "O" << std::flush;
+          break;
+        } else {
+//          std::cerr << "." << std::flush;
+        }
+      }
+
+      _buf_used = 0;
+      break;
+    }
+
+    *buf++ = (in[i].real() + 1.0) * 127;
+    *buf++ = (in[i].imag() + 1.0) * 127;
+
+    _buf_used += BYTES_PER_SAMPLE;
+    items_consumed++;
+  }
+
+  noutput_items = items_consumed;
+
+  // Tell runtime system how many input items we consumed on
+  // each input stream.
+  consume_each(noutput_items);
+
+  // Tell runtime system how many output items we produced.
+  return 0;
+}
+
+std::vector<std::string> hackrf_sink_c::get_devices()
+{
+  std::vector<std::string> devices;
+  std::string label;
+
+  for (unsigned int i = 0; i < 1 /* TODO: missing libhackrf api */; i++) {
+    std::string args = "hackrf=" + boost::lexical_cast< std::string >( i );
+
+    label.clear();
+
+    label = "HackRF Jawbreaker"; /* TODO: missing libhackrf api */
+
+    boost::algorithm::trim(label);
+
+    args += ",label='" + label + "'";
+    devices.push_back( args );
+  }
+
+  return devices;
+}
+
+size_t hackrf_sink_c::get_num_channels()
+{
+  return 1;
+}
+
+osmosdr::meta_range_t hackrf_sink_c::get_sample_rates()
+{
+  osmosdr::meta_range_t range;
+
+  range += osmosdr::range_t( 5e6 ); /* out of spec but appears to work */
+  range += osmosdr::range_t( 10e6 );
+  range += osmosdr::range_t( 12.5e6 );
+  range += osmosdr::range_t( 16e6 );
+  range += osmosdr::range_t( 20e6 ); /* confirmed to work on fast machines */
+
+  return range;
+}
+
+double hackrf_sink_c::set_sample_rate(double rate)
+{
+  int ret;
+
+  if (_dev) {
+    ret = hackrf_sample_rate_set( _dev, uint32_t(rate) );
+    if ( HACKRF_SUCCESS == ret ) {
+      _sample_rate = rate;
+      set_bandwidth( rate );
+    } else {
+      throw std::runtime_error( std::string( __FUNCTION__ ) + " has failed" );
+    }
+  }
+
+  return get_sample_rate();
+}
+
+double hackrf_sink_c::get_sample_rate()
+{
+  return _sample_rate;
+}
+
+osmosdr::freq_range_t hackrf_sink_c::get_freq_range( size_t chan )
+{
+  osmosdr::freq_range_t range;
+
+  range += osmosdr::range_t( 30e6, 6e9 );
+
+  return range;
+}
+
+double hackrf_sink_c::set_center_freq( double freq, size_t chan )
+{
+  int ret;
+
+  #define APPLY_PPM_CORR(val, ppm) ((val) * (1.0 + (ppm) * 0.000001))
+
+  if (_dev) {
+    double corr_freq = APPLY_PPM_CORR( freq, _freq_corr );
+    ret = hackrf_set_freq( _dev, uint64_t(corr_freq) );
+    if ( HACKRF_SUCCESS == ret ) {
+      _center_freq = freq;
+    } else {
+      throw std::runtime_error( std::string( __FUNCTION__ ) + " has failed" );
+    }
+  }
+
+  return get_center_freq( chan );
+}
+
+double hackrf_sink_c::get_center_freq( size_t chan )
+{
+  return _center_freq;
+}
+
+double hackrf_sink_c::set_freq_corr( double ppm, size_t chan )
+{
+  _freq_corr = ppm;
+
+  set_center_freq( _center_freq );
+
+  return get_freq_corr( chan );
+}
+
+double hackrf_sink_c::get_freq_corr( size_t chan )
+{
+  return _freq_corr;
+}
+
+std::vector<std::string> hackrf_sink_c::get_gain_names( size_t chan )
+{
+  std::vector< std::string > names;
+
+  names += "RF";
+  names += "IF";
+
+  return names;
+}
+
+osmosdr::gain_range_t hackrf_sink_c::get_gain_range( size_t chan )
+{
+  return get_gain_range( "RF", chan );
+}
+
+osmosdr::gain_range_t hackrf_sink_c::get_gain_range( const std::string & name, size_t chan )
+{
+  if ( "RF" == name ) {
+    return osmosdr::gain_range_t( 0, 14, 14 );
+  }
+
+  if ( "IF" == name ) {
+    return osmosdr::gain_range_t( 0, 47, 1 );
+  }
+
+  return osmosdr::gain_range_t();
+}
+
+bool hackrf_sink_c::set_gain_mode( bool automatic, size_t chan )
+{
+  _auto_gain = automatic;
+
+  return get_gain_mode(chan);
+}
+
+bool hackrf_sink_c::get_gain_mode( size_t chan )
+{
+  return _auto_gain;
+}
+
+double hackrf_sink_c::set_gain( double gain, size_t chan )
+{
+  osmosdr::gain_range_t rf_gains = get_gain_range( "RF", chan );
+
+  if (_dev) {
+    double clip_gain = rf_gains.clip( gain, true );
+
+    std::map<double, int> reg_vals;
+    reg_vals[ 0 ] = 0;
+    reg_vals[ 14 ] = 1;
+
+    if ( reg_vals.count( clip_gain ) ) {
+      int value = reg_vals[ clip_gain ];
+#if 0
+      std::cerr << "amp gain: " << gain
+                << " clip_gain: " << clip_gain
+                << " value: " << value
+                << std::endl;
+#endif
+      if ( hackrf_set_amp_enable( _dev, value ) == HACKRF_SUCCESS )
+        _amp_gain = clip_gain;
+    }
+  }
+
+  return _amp_gain;
+}
+
+double hackrf_sink_c::set_gain( double gain, const std::string & name, size_t chan)
+{
+  if ( "RF" == name ) {
+    return set_gain( gain, chan );
+  }
+
+  if ( "IF" == name ) {
+    return set_if_gain( gain, chan );
+  }
+
+  return set_gain( gain, chan );
+}
+
+double hackrf_sink_c::get_gain( size_t chan )
+{
+  return _amp_gain;
+}
+
+double hackrf_sink_c::get_gain( const std::string & name, size_t chan )
+{
+  if ( "RF" == name ) {
+    return get_gain( chan );
+  }
+
+  if ( "IF" == name ) {
+    return _vga_gain;
+  }
+
+  return get_gain( chan );
+}
+
+double hackrf_sink_c::set_if_gain( double gain, size_t chan )
+{
+  osmosdr::gain_range_t if_gains = get_gain_range( "IF", chan );
+
+  double clip_gain = if_gains.clip( gain, true );
+  double rel_atten = fabs( if_gains.stop() - clip_gain );
+
+  std::vector< osmosdr::gain_range_t > if_attens;
+
+  if_attens += osmosdr::gain_range_t(0, 1, 1); /* chapter 1.5: TX Gain Control */
+  if_attens += osmosdr::gain_range_t(0, 2, 2);
+  if_attens += osmosdr::gain_range_t(0, 4, 4);
+  if_attens += osmosdr::gain_range_t(0, 8, 8);
+  if_attens += osmosdr::gain_range_t(0, 16, 16);
+  if_attens += osmosdr::gain_range_t(0, 16, 16);
+
+  std::map< int, double > attens;
+
+  /* initialize with min attens */
+  for (unsigned int i = 0; i < if_attens.size(); i++) {
+    attens[ i + 1 ] = if_attens[ i ].start();
+  }
+
+  double atten = rel_atten;
+
+  for (int i = if_attens.size() - 1; i >= 0; i--) {
+    osmosdr::gain_range_t range = if_attens[ i ];
+
+    if ( atten - range.stop() >= 0 ) {
+      atten -= range.stop();
+      attens[ i + 1 ] = range.stop();
+    }
+  }
+#if 0
+  std::cerr << rel_atten << " => "; double sum = 0;
+  for (unsigned int i = 0; i < attens.size(); i++) {
+    sum += attens[ i + 1 ];
+    std::cerr << attens[ i + 1 ] << " ";
+  }
+  std::cerr << " = " << sum << std::endl;
+#endif
+  if (_dev) {
+    int value = 0;
+    for (unsigned int stage = 1; stage <= attens.size(); stage++) {
+      if ( attens[ stage ] != 0 )
+        value |= 1 << (stage - 1);
+    }
+#if 0
+    std::cerr << "vga gain: " << gain
+              << " clip_gain: " << clip_gain
+              << " rel_atten: " << rel_atten
+              << " value: " << value
+              << std::endl;
+#endif
+    uint16_t val;
+    hackrf_max2837_read( _dev, 29, &val );
+
+    val = (val & 0xf) | ((value & 0x3f) << 4);
+
+    if ( hackrf_max2837_write( _dev, 29, val ) == HACKRF_SUCCESS )
+      _vga_gain = clip_gain;
+  }
+
+  return _vga_gain;
+}
+
+double hackrf_sink_c::set_bb_gain(double gain, size_t chan)
+{
+  return 0;
+}
+
+std::vector< std::string > hackrf_sink_c::get_antennas( size_t chan )
+{
+  std::vector< std::string > antennas;
+
+  antennas += get_antenna( chan );
+
+  return antennas;
+}
+
+std::string hackrf_sink_c::set_antenna( const std::string & antenna, size_t chan )
+{
+  return get_antenna( chan );
+}
+
+std::string hackrf_sink_c::get_antenna( size_t chan )
+{
+  return "ANT";
+}
+
+double hackrf_sink_c::set_bandwidth( double bandwidth, size_t chan )
+{
+  int ret;
+//  osmosdr::meta_range_t bandwidths = get_bandwidth_range( chan );
+
+  if ( bandwidth == 0.0 ) /* bandwidth of 0 means automatic filter selection */
+    bandwidth = _sample_rate;
+
+  if ( _dev ) {
+    /* compute best default value depending on sample rate (auto filter) */
+    uint32_t bw = hackrf_compute_baseband_filter_bw( uint32_t(bandwidth) );
+    ret = hackrf_baseband_filter_bandwidth_set( _dev, bw );
+    if ( HACKRF_SUCCESS == ret ) {
+      _bandwidth = bw;
+    } else {
+      throw std::runtime_error( std::string( __FUNCTION__ ) + " has failed" );
+    }
+  }
+
+  return _bandwidth;
+}
+
+double hackrf_sink_c::get_bandwidth( size_t chan )
+{
+  return _bandwidth;
+}
+
+osmosdr::meta_range_t hackrf_sink_c::get_bandwidth_range( size_t chan )
+{
+  osmosdr::meta_range_t bandwidths;
+
+  // TODO: read out from libhackrf when an API is available
+
+  bandwidths += osmosdr::range_t( 1750000 );
+  bandwidths += osmosdr::range_t( 2500000 );
+  bandwidths += osmosdr::range_t( 3500000 );
+  bandwidths += osmosdr::range_t( 5000000 );
+  bandwidths += osmosdr::range_t( 5500000 );
+  bandwidths += osmosdr::range_t( 6000000 );
+  bandwidths += osmosdr::range_t( 7000000 );
+  bandwidths += osmosdr::range_t( 8000000 );
+  bandwidths += osmosdr::range_t( 9000000 );
+  bandwidths += osmosdr::range_t( 10000000 );
+  bandwidths += osmosdr::range_t( 12000000 );
+  bandwidths += osmosdr::range_t( 14000000 );
+  bandwidths += osmosdr::range_t( 15000000 );
+  bandwidths += osmosdr::range_t( 20000000 );
+  bandwidths += osmosdr::range_t( 24000000 );
+  bandwidths += osmosdr::range_t( 28000000 );
 
+  return bandwidths;
 }
diff --git a/lib/hackrf/hackrf_sink_c.h b/lib/hackrf/hackrf_sink_c.h
index a0a045e..4c0ca5f 100644
--- a/lib/hackrf/hackrf_sink_c.h
+++ b/lib/hackrf/hackrf_sink_c.h
@@ -20,10 +20,29 @@
 #ifndef INCLUDED_HACKRF_SINK_C_H
 #define INCLUDED_HACKRF_SINK_C_H
 
-#include <boost/shared_ptr.hpp>
+#include <gruel/thread.h>
+#include <gnuradio/gr_sync_block.h>
+
+#include <boost/thread/mutex.hpp>
+#include <boost/thread/condition_variable.hpp>
+
+#include <libhackrf/hackrf.h>
+
+#include "osmosdr_snk_iface.h"
 
 class hackrf_sink_c;
 
+typedef struct circular_buffer
+{
+  void *buffer;     // data buffer
+  void *buffer_end; // end of data buffer
+  size_t capacity;  // maximum number of items in the buffer
+  size_t count;     // number of items in the buffer
+  size_t sz;        // size of each item in the buffer
+  void *head;       // pointer to head
+  void *tail;       // pointer to tail
+} circular_buffer_t;
+
 /*
  * We use boost::shared_ptr's instead of raw pointers for all access
  * to gr_blocks (and many other data structures).  The shared_ptr gets
@@ -46,7 +65,9 @@ typedef boost::shared_ptr<hackrf_sink_c> hackrf_sink_c_sptr;
  */
 hackrf_sink_c_sptr make_hackrf_sink_c (const std::string & args = "");
 
-class hackrf_sink_c
+class hackrf_sink_c :
+    public gr_sync_block,
+    public osmosdr_snk_iface
 {
 private:
   // The friend declaration allows hackrf_make_sink_c to
@@ -56,7 +77,78 @@ private:
   hackrf_sink_c (const std::string & args);  	// private constructor
 
 public:
-  ~hackrf_source_c (); 	// public destructor
+  ~hackrf_sink_c (); 	// public destructor
+
+  bool start();
+  bool stop();
+
+  int work( int noutput_items,
+            gr_vector_const_void_star &input_items,
+            gr_vector_void_star &output_items );
+
+  static std::vector< std::string > get_devices();
+
+  size_t get_num_channels( void );
+
+  osmosdr::meta_range_t get_sample_rates( void );
+  double set_sample_rate( double rate );
+  double get_sample_rate( void );
+
+  osmosdr::freq_range_t get_freq_range( size_t chan = 0 );
+  double set_center_freq( double freq, size_t chan = 0 );
+  double get_center_freq( size_t chan = 0 );
+  double set_freq_corr( double ppm, size_t chan = 0 );
+  double get_freq_corr( size_t chan = 0 );
+
+  std::vector<std::string> get_gain_names( size_t chan = 0 );
+  osmosdr::gain_range_t get_gain_range( size_t chan = 0 );
+  osmosdr::gain_range_t get_gain_range( const std::string & name, size_t chan = 0 );
+  bool set_gain_mode( bool automatic, size_t chan = 0 );
+  bool get_gain_mode( size_t chan = 0 );
+  double set_gain( double gain, size_t chan = 0 );
+  double set_gain( double gain, const std::string & name, size_t chan = 0 );
+  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 );
+  double set_bb_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 );
+
+  double set_bandwidth( double bandwidth, size_t chan = 0 );
+  double get_bandwidth( size_t chan = 0 );
+  osmosdr::meta_range_t get_bandwidth_range( size_t chan = 0 );
+
+private:
+  static int _hackrf_tx_callback(hackrf_transfer* transfer);
+  int hackrf_tx_callback(unsigned char *buffer, uint32_t length);
+  static void _hackrf_wait(hackrf_sink_c *obj);
+  void hackrf_wait();
+
+  static int _usage;
+  static boost::mutex _usage_mutex;
+
+  std::vector<gr_complex> _lut;
+
+  hackrf_device *_dev;
+//  gruel::thread _thread;
+
+  circular_buffer_t _cbuf;
+  unsigned char *_buf;
+  unsigned int _buf_num;
+  unsigned int _buf_used;
+  boost::mutex _buf_mutex;
+  boost::condition_variable _buf_cond;
+
+  double _sample_rate;
+  double _center_freq;
+  double _freq_corr;
+  bool _auto_gain;
+  double _amp_gain;
+  double _vga_gain;
+  double _bandwidth;
 };
 
 #endif /* INCLUDED_HACKRF_SINK_C_H */
diff --git a/lib/osmosdr_sink_c_impl.cc b/lib/osmosdr_sink_c_impl.cc
index dce2f08..6152069 100644
--- a/lib/osmosdr_sink_c_impl.cc
+++ b/lib/osmosdr_sink_c_impl.cc
@@ -1,6 +1,6 @@
 /* -*- c++ -*- */
 /*
- * Copyright 2012 Dimitri Stolnikov <horiz0n@gmx.net>
+ * Copyright 2013 Dimitri Stolnikov <horiz0n@gmx.net>
  *
  * GNU Radio is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -27,8 +27,22 @@
 #include "config.h"
 #endif
 
-#include <osmosdr_sink_c_impl.h>
-#include <gr_io_signature.h>
+#include <gnuradio/gr_io_signature.h>
+#include <gnuradio/gr_constants.h>
+#include <gnuradio/gr_throttle.h>
+#include <gnuradio/gr_null_sink.h>
+
+#include "osmosdr_sink_c_impl.h"
+
+#ifdef ENABLE_HACKRF
+#include "hackrf_sink_c.h"
+#endif
+
+#include "osmosdr_arg_helpers.h"
+
+/* This avoids throws in ctor of gr_hier_block2, as gnuradio is unable to deal
+ with this behavior in a clean way. The GR maintainer Rondeau has been informed. */
+#define WORKAROUND_GR_HIER_BLOCK2_BUG
 
 /*
  * Create a new instance of osmosdr_sink_c_impl and return
@@ -41,26 +55,448 @@ osmosdr_make_sink_c (const std::string &args)
 }
 
 /*
- * Specify constraints on number of input and output streams.
- * This info is used to construct the input and output signatures
- * (2nd & 3rd args to gr_block's constructor).  The input and
- * output signatures are used by the runtime system to
- * check that a valid number and type of inputs and outputs
- * are connected to this block.  In this case, we accept
- * only 1 input and 0 output.
- */
-static const int MIN_IN = 1;	// mininum number of input streams
-static const int MAX_IN = 1;	// maximum number of input streams
-static const int MIN_OUT = 0;	// minimum number of output streams
-static const int MAX_OUT = 0;	// maximum number of output streams
-
-/*
  * The private constructor
  */
 osmosdr_sink_c_impl::osmosdr_sink_c_impl (const std::string &args)
   : gr_hier_block2 ("osmosdr_sink_c_impl",
-        gr_make_io_signature (MIN_IN, MAX_IN, sizeof (gr_complex)),
-        gr_make_io_signature (MIN_OUT, MAX_OUT, sizeof (gr_complex)))
+        args_to_io_signature(args),
+        gr_make_io_signature (0, 0, 0))
+{
+  size_t channel = 0;
+  bool device_specified = false;
+
+  std::vector< std::string > arg_list = args_to_vector(args);
+
+  std::vector< std::string > dev_types;
+
+#ifdef ENABLE_HACKRF
+  dev_types.push_back("hackrf");
+#endif
+
+  std::cerr << "gr-osmosdr "
+            << GR_OSMOSDR_VERSION " (" GR_OSMOSDR_LIBVER ") "
+            << "gnuradio " << gr_version() << std::endl;
+  std::cerr << "built-in device types: ";
+  BOOST_FOREACH(std::string dev_type, dev_types)
+    std::cerr << dev_type << " ";
+  std::cerr << std::endl << std::flush;
+
+  BOOST_FOREACH(std::string arg, arg_list) {
+    dict_t dict = params_to_dict(arg);
+    BOOST_FOREACH(std::string dev_type, dev_types) {
+      if ( dict.count( dev_type ) ) {
+        device_specified = true;
+        break;
+      }
+    }
+  }
+#ifdef WORKAROUND_GR_HIER_BLOCK2_BUG
+  try {
+#endif
+  std::vector< std::string > dev_list;
+#ifdef ENABLE_HACKRF
+  BOOST_FOREACH( std::string dev, hackrf_sink_c::get_devices() )
+  dev_list.push_back( dev );
+#endif
+//  std::cerr << std::endl;
+//  BOOST_FOREACH( std::string dev, dev_list )
+//    std::cerr << "'" << dev << "'" << std::endl;
+
+  if (!device_specified) {
+    if ( dev_list.size() )
+      arg_list.push_back( dev_list.front() );
+    else
+      throw std::runtime_error("No supported devices found to pick from.");
+  }
+
+  BOOST_FOREACH(std::string arg, arg_list) {
+
+    dict_t dict = params_to_dict(arg);
+
+//    std::cerr << std::endl;
+//    BOOST_FOREACH( dict_t::value_type &entry, dict )
+//      std::cerr << "'" << entry.first << "' = '" << entry.second << "'" << std::endl;
+
+    osmosdr_snk_iface *iface = NULL;
+    gr_basic_block_sptr block;
+
+#ifdef ENABLE_HACKRF
+    if ( dict.count("hackrf") ) {
+      hackrf_sink_c_sptr src = make_hackrf_sink_c( arg );
+      block = src; iface = src.get();
+    }
+#endif
+
+    if ( iface != NULL && long(block.get()) != 0 ) {
+      _devs.push_back( iface );
+
+      for (size_t i = 0; i < iface->get_num_channels(); i++) {
+        connect(self(), channel++, block, i);
+      }
+    } else if ( (iface != NULL) || (long(block.get()) != 0) )
+      throw std::runtime_error("Eitner iface or block are NULL.");
+
+  }
+
+  if (!_devs.size())
+    throw std::runtime_error("No devices specified via device arguments.");
+#ifdef WORKAROUND_GR_HIER_BLOCK2_BUG
+  } catch ( std::exception &ex ) {
+    std::cerr << std::endl << "FATAL: " << ex.what() << std::endl << std::endl;
+
+    size_t missing_chans = output_signature()->max_streams() - channel;
+
+    std::cerr << "Trying to fill up " << missing_chans
+              << " missing channel(s) with null sinks.\n"
+              << "This is being done to prevent the application from crashing\n"
+              << "due to a gnuradio bug. The maintainers have been informed.\n"
+              << std::endl;
+
+    for (size_t i = 0; i < missing_chans; i++) {
+      /* we try to prevent the whole application from crashing by faking
+       * the missing hardware (channels) with a null sink */
+      gr_null_sink_sptr null_sink =  gr_make_null_sink( sizeof(gr_complex) );
+
+      gr_throttle::sptr throttle = gr_make_throttle(sizeof(gr_complex), 1e6);
+
+      connect(self(), channel++, throttle, 0);
+      connect(throttle, 0, null_sink, 0);
+    }
+  }
+#endif
+}
+
+size_t osmosdr_sink_c_impl::get_num_channels()
+{
+  size_t channels = 0;
+
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    channels += dev->get_num_channels();
+
+  return channels;
+}
+
+#define NO_DEVICES_MSG  "FATAL: No device(s) available to work with."
+
+osmosdr::meta_range_t osmosdr_sink_c_impl::get_sample_rates()
+{
+  osmosdr::meta_range_t rates(0, 0, 0);
+
+  if (!_devs.empty())
+    rates = _devs[0]->get_sample_rates(); // assume same devices used in the group
+#if 0
+  else
+    throw std::runtime_error(NO_DEVICES_MSG);
+#endif
+  return rates;
+}
+
+double osmosdr_sink_c_impl::set_sample_rate(double rate)
+{
+  double sample_rate = 0;
+
+  if (_sample_rate != rate) {
+#if 0
+    if (_devs.empty())
+      throw std::runtime_error(NO_DEVICES_MSG);
+#endif
+    BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+      sample_rate = dev->set_sample_rate(rate);
+
+    _sample_rate = sample_rate;
+  }
+
+  return sample_rate;
+}
+
+double osmosdr_sink_c_impl::get_sample_rate()
+{
+  double sample_rate = 0;
+
+  if (!_devs.empty())
+    sample_rate = _devs[0]->get_sample_rate(); // assume same devices used in the group
+#if 0
+  else
+    throw std::runtime_error(NO_DEVICES_MSG);
+#endif
+  return sample_rate;
+}
+
+osmosdr::freq_range_t osmosdr_sink_c_impl::get_freq_range( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_freq_range( dev_chan );
+
+  return osmosdr::freq_range_t();
+}
+
+double osmosdr_sink_c_impl::set_center_freq( double freq, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _center_freq[ chan ] != freq ) {
+          _center_freq[ chan ] = freq;
+          return dev->set_center_freq( freq, dev_chan );
+        }
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::get_center_freq( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_center_freq( dev_chan );
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::set_freq_corr( double ppm, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _freq_corr[ chan ] != ppm ) {
+          _freq_corr[ chan ] = ppm;
+          return dev->set_freq_corr( ppm, dev_chan );
+        }
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::get_freq_corr( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_freq_corr( dev_chan );
+
+  return 0;
+}
+
+std::vector<std::string> osmosdr_sink_c_impl::get_gain_names( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_gain_names( dev_chan );
+
+  return std::vector< std::string >();
+}
+
+osmosdr::gain_range_t osmosdr_sink_c_impl::get_gain_range( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_gain_range( dev_chan );
+
+  return osmosdr::gain_range_t();
+}
+
+osmosdr::gain_range_t osmosdr_sink_c_impl::get_gain_range( const std::string & name, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_gain_range( name, dev_chan );
+
+  return osmosdr::gain_range_t();
+}
+
+bool osmosdr_sink_c_impl::set_gain_mode( bool automatic, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _gain_mode[ chan ] != automatic ) {
+          _gain_mode[ chan ] = automatic;
+          bool mode = dev->set_gain_mode( automatic, dev_chan );
+          if (!automatic) // reapply gain value when switched to manual mode
+            dev->set_gain( _gain[ chan ], dev_chan );
+          return mode;
+        }
+
+  return false;
+}
+
+bool osmosdr_sink_c_impl::get_gain_mode( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_gain_mode( dev_chan );
+
+  return false;
+}
+
+double osmosdr_sink_c_impl::set_gain( double gain, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _gain[ chan ] != gain ) {
+          _gain[ chan ] = gain;
+          return dev->set_gain( gain, dev_chan );
+        }
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::set_gain( double gain, const std::string & name, size_t chan)
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->set_gain( gain, name, dev_chan );
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::get_gain( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_gain( dev_chan );
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::get_gain( const std::string & name, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_gain( name, dev_chan );
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::set_if_gain( double gain, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _if_gain[ chan ] != gain ) {
+          _if_gain[ chan ] = gain;
+          return dev->set_if_gain( gain, dev_chan );
+        }
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::set_bb_gain( double gain, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _bb_gain[ chan ] != gain ) {
+          _bb_gain[ chan ] = gain;
+          return dev->set_bb_gain( gain, dev_chan );
+        }
+
+  return 0;
+}
+
+std::vector< std::string > osmosdr_sink_c_impl::get_antennas( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_antennas( dev_chan );
+
+  return std::vector< std::string >();
+}
+
+std::string osmosdr_sink_c_impl::set_antenna( const std::string & antenna, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _antenna[ chan ] != antenna ) {
+          _antenna[ chan ] = antenna;
+          return dev->set_antenna( antenna, dev_chan );
+        }
+
+  return "";
+}
+
+std::string osmosdr_sink_c_impl::get_antenna( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_antenna( dev_chan );
+
+  return "";
+}
+
+void osmosdr_sink_c_impl::set_iq_balance_mode( int mode, size_t chan )
+{
+
+}
+
+void osmosdr_sink_c_impl::set_iq_balance( const std::complex<double> &correction, size_t chan )
+{
+
+}
+
+double osmosdr_sink_c_impl::set_bandwidth( double bandwidth, size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        if ( _bandwidth[ chan ] != bandwidth ) {
+          _bandwidth[ chan ] = bandwidth;
+          return dev->set_bandwidth( bandwidth, dev_chan );
+        }
+
+  return 0;
+}
+
+double osmosdr_sink_c_impl::get_bandwidth( size_t chan )
+{
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_bandwidth( dev_chan );
+
+  return 0;
+}
+
+osmosdr::meta_range_t osmosdr_sink_c_impl::get_bandwidth_range( size_t chan )
 {
+  size_t channel = 0;
+  BOOST_FOREACH( osmosdr_snk_iface *dev, _devs )
+    for (size_t dev_chan = 0; dev_chan < dev->get_num_channels(); dev_chan++)
+      if ( chan == channel++ )
+        return dev->get_bandwidth_range( dev_chan );
 
+  return osmosdr::meta_range_t();
 }
diff --git a/lib/osmosdr_sink_c_impl.h b/lib/osmosdr_sink_c_impl.h
index 49457d0..9194168 100644
--- a/lib/osmosdr_sink_c_impl.h
+++ b/lib/osmosdr_sink_c_impl.h
@@ -1,6 +1,6 @@
 /* -*- c++ -*- */
 /*
- * Copyright 2012 Dimitri Stolnikov <horiz0n@gmx.net>
+ * Copyright 2013 Dimitri Stolnikov <horiz0n@gmx.net>
  *
  * GNU Radio is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,11 +20,50 @@
 #ifndef INCLUDED_OSMOSDR_SINK_C_IMPL_H
 #define INCLUDED_OSMOSDR_SINK_C_IMPL_H
 
-#include <osmosdr/osmosdr_sink_c.h>
+#include "osmosdr/osmosdr_sink_c.h"
+
+#include "osmosdr_snk_iface.h"
+
+#include <map>
 
 class osmosdr_sink_c_impl : public osmosdr_sink_c
 {
 public:
+  size_t get_num_channels( void );
+
+  osmosdr::meta_range_t get_sample_rates( void );
+  double set_sample_rate( double rate );
+  double get_sample_rate( void );
+
+  osmosdr::freq_range_t get_freq_range( size_t chan = 0 );
+  double set_center_freq( double freq, size_t chan = 0 );
+  double get_center_freq( size_t chan = 0 );
+  double set_freq_corr( double ppm, size_t chan = 0 );
+  double get_freq_corr( size_t chan = 0 );
+
+  std::vector<std::string> get_gain_names( size_t chan = 0 );
+  osmosdr::gain_range_t get_gain_range( size_t chan = 0 );
+  osmosdr::gain_range_t get_gain_range( const std::string & name, size_t chan = 0 );
+  bool set_gain_mode( bool automatic, size_t chan = 0 );
+  bool get_gain_mode( size_t chan = 0 );
+  double set_gain( double gain, size_t chan = 0 );
+  double set_gain( double gain, const std::string & name, size_t chan = 0 );
+  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 );
+  double set_bb_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 );
+
+  void set_iq_balance_mode( int mode, size_t chan = 0 );
+  void set_iq_balance( const std::complex<double> &correction, size_t chan = 0 );
+
+  double set_bandwidth( double bandwidth, size_t chan = 0 );
+  double get_bandwidth( size_t chan = 0 );
+  osmosdr::meta_range_t get_bandwidth_range( size_t chan = 0 );
 
 private:
   osmosdr_sink_c_impl (const std::string & args);  	// private constructor
@@ -32,6 +71,18 @@ private:
   // The friend declaration allows osmosdr_make_sink_c to
   // access the private constructor.
   friend osmosdr_sink_c_sptr osmosdr_make_sink_c (const std::string & args);
+
+  std::vector< osmosdr_snk_iface * > _devs;
+
+  double _sample_rate;
+  std::map< size_t, double > _center_freq;
+  std::map< size_t, double > _freq_corr;
+  std::map< size_t, bool > _gain_mode;
+  std::map< size_t, double > _gain;
+  std::map< size_t, double > _if_gain;
+  std::map< size_t, double > _bb_gain;
+  std::map< size_t, std::string > _antenna;
+  std::map< size_t, double > _bandwidth;
 };
 
 #endif /* INCLUDED_OSMOSDR_SINK_C_IMPL_H */
diff --git a/lib/osmosdr_snk_iface.h b/lib/osmosdr_snk_iface.h
new file mode 100644
index 0000000..4a45529
--- /dev/null
+++ b/lib/osmosdr_snk_iface.h
@@ -0,0 +1,261 @@
+/* -*- c++ -*- */
+/*
+ * Copyright 2012 Dimitri Stolnikov <horiz0n@gmx.net>
+ *
+ * GNU Radio is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3, or (at your option)
+ * any later version.
+ *
+ * GNU Radio is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Radio; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#ifndef OSMOSDR_SNK_IFACE_H
+#define OSMOSDR_SNK_IFACE_H
+
+#include <osmosdr/osmosdr_ranges.h>
+#include <gr_basic_block.h>
+
+class osmosdr_snk_iface;
+
+typedef boost::shared_ptr<osmosdr_snk_iface> osmosdr_snk_iface_sptr;
+
+/*!
+ * TODO: document
+ *
+ */
+class osmosdr_snk_iface
+{
+public:
+  /*!
+   * Get the number of channels the underlying radio hardware offers.
+   * \return the number of available channels
+   */
+  virtual size_t get_num_channels( void ) = 0;
+
+  /*!
+   * Get the possible sample rates for the underlying radio hardware.
+   * \return a range of rates in Sps
+   */
+  virtual osmosdr::meta_range_t get_sample_rates( void ) = 0;
+
+  /*!
+   * Set the sample rate for the underlying radio hardware.
+   * This also will select the appropriate IF bandpass, if applicable.
+   * \param rate a new rate in Sps
+   */
+  virtual double set_sample_rate( double rate ) = 0;
+
+  /*!
+   * Get the sample rate for the underlying radio hardware.
+   * This is the actual sample rate and may differ from the rate set.
+   * \return the actual rate in Sps
+   */
+  virtual double get_sample_rate( void ) = 0;
+
+  /*!
+   * Get the tunable frequency range for the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return the frequency range in Hz
+   */
+  virtual osmosdr::freq_range_t get_freq_range( size_t chan = 0 ) = 0;
+
+  /*!
+   * Tune the underlying radio hardware to the desired center frequency.
+   * This also will select the appropriate RF bandpass.
+   * \param freq the desired frequency in Hz
+   * \param chan the channel index 0 to N-1
+   * \return the actual frequency in Hz
+   */
+  virtual double set_center_freq( double freq, size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the center frequency the underlying radio hardware is tuned to.
+   * This is the actual frequency and may differ from the frequency set.
+   * \param chan the channel index 0 to N-1
+   * \return the frequency in Hz
+   */
+  virtual double get_center_freq( size_t chan = 0 ) = 0;
+
+  /*!
+   * Set the frequency correction value in parts per million.
+   * \param ppm the desired correction value in parts per million
+   * \param chan the channel index 0 to N-1
+   * \return correction value in parts per million
+   */
+  virtual double set_freq_corr( double ppm, size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the frequency correction value.
+   * \param chan the channel index 0 to N-1
+   * \return correction value in parts per million
+   */
+  virtual double get_freq_corr( size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the gain stage names of the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return a vector of strings containing the names of gain stages
+   */
+  virtual std::vector<std::string> get_gain_names( size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the settable overall gain range for the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return the gain range in dB
+   */
+  virtual osmosdr::gain_range_t get_gain_range( size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the settable gain range for a specific gain stage.
+   * \param name the name of the gain stage
+   * \param chan the channel index 0 to N-1
+   * \return the gain range in dB
+   */
+  virtual osmosdr::gain_range_t get_gain_range( const std::string & name,
+                                                size_t chan = 0 ) = 0;
+
+  /*!
+   * Set the gain mode for the underlying radio hardware.
+   * This might be supported only for certain hardware types.
+   * \param automatic the gain mode (true means automatic gain mode)
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain mode
+   */
+  virtual bool set_gain_mode( bool automatic, size_t chan = 0 ) { return false; }
+
+  /*!
+   * Get the gain mode selected for the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain mode (true means automatic gain mode)
+   */
+  virtual bool get_gain_mode( size_t chan = 0 ) { return false; }
+
+  /*!
+   * Set the gain for the underlying radio hardware.
+   * This function will automatically distribute the desired gain value over
+   * available gain stages in an appropriate way and return the actual value.
+   * \param gain the gain in dB
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain in dB
+   */
+  virtual double set_gain( double gain, size_t chan = 0 ) = 0;
+
+  /*!
+   * Set the named gain on the underlying radio hardware.
+   * \param gain the gain in dB
+   * \param name the name of the gain stage
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain in dB
+   */
+  virtual double set_gain( double gain,
+                           const std::string & name,
+                           size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the actual gain setting of the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain in dB
+   */
+  virtual double get_gain( size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the actual gain setting of a named stage.
+   * \param name the name of the gain stage
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain in dB
+   */
+  virtual double get_gain( const std::string & name, size_t chan = 0 ) = 0;
+
+  /*!
+   * Set the IF gain for the underlying radio hardware.
+   * This function will automatically distribute the desired gain value over
+   * available IF gain stages in an appropriate way and return the actual value.
+   * \param gain the gain in dB
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain in dB
+   */
+  virtual double set_if_gain( double gain, size_t chan = 0 ) { return 0; }
+
+  /*!
+   * Set the BB gain for the underlying radio hardware.
+   * This function will automatically distribute the desired gain value over
+   * available BB gain stages in an appropriate way and return the actual value.
+   * \param gain the gain in dB
+   * \param chan the channel index 0 to N-1
+   * \return the actual gain in dB
+   */
+  virtual double set_bb_gain( double gain, size_t chan = 0 ) { return 0; }
+
+  /*!
+   * Get the available antennas of the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return a vector of strings containing the names of available antennas
+   */
+  virtual std::vector< std::string > get_antennas( size_t chan = 0 ) = 0;
+
+  /*!
+   * Select the active antenna of the underlying radio hardware.
+   * \param chan the channel index 0 to N-1
+   * \return the actual antenna's name
+   */
+  virtual std::string set_antenna( const std::string & antenna,
+                                   size_t chan = 0 ) = 0;
+
+  /*!
+   * Get the actual underlying radio hardware antenna setting.
+   * \param chan the channel index 0 to N-1
+   * \return the actual antenna's name
+   */
+  virtual std::string get_antenna( size_t chan = 0 ) = 0;
+
+  /*!
+   * Set the TX frontend IQ balance mode.
+   *
+   * \param mode iq balance correction mode: 0 = Off, 1 = Manual, 2 = Automatic
+   * \param chan the channel index 0 to N-1
+   */
+  virtual void set_iq_balance_mode( int mode, size_t chan = 0 ) { }
+
+  /*!
+   * Set the TX frontend IQ balance correction.
+   * Use this to adjust the magnitude and phase of I and Q.
+   *
+   * \param correction the complex correction value
+   * \param chan the channel index 0 to N-1
+   */
+  virtual void set_iq_balance( const std::complex<double> &correction, size_t chan = 0 ) { }
+
+  /*!
+   * Set the bandpass filter on the radio frontend.
+   * \param bandwidth the filter bandwidth in Hz
+   * \param chan the channel index 0 to N-1
+   * \return the actual filter bandwidth in Hz
+   */
+  virtual double set_bandwidth( double bandwidth, size_t chan = 0 ) { return 0; }
+
+  /*!
+   * Get the actual bandpass filter setting on the radio frontend.
+   * \param chan the channel index 0 to N-1
+   * \return the actual filter bandwidth in Hz
+   */
+  virtual double get_bandwidth( size_t chan = 0 ) { return 0; }
+
+  /*!
+   * Get the possible bandpass filter settings on the radio frontend.
+   * \param chan the channel index 0 to N-1
+   * \return a range of bandwidths in Hz
+   */
+  virtual osmosdr::meta_range_t get_bandwidth_range( size_t chan = 0 )
+    { return osmosdr::meta_range_t(); }
+};
+
+#endif // OSMOSDR_SNK_IFACE_H