5 files changed, 35 insertions, 19 deletions
diff --git a/gr-uhd/apps/uhd_app.py b/gr-uhd/apps/uhd_app.py
index 59bebe24ec..ff4412a140 100644
--- a/gr-uhd/apps/uhd_app.py
+++ b/gr-uhd/apps/uhd_app.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 #
-# Copyright 2015 Free Software Foundation, Inc.
+# Copyright 2015-2016 Free Software Foundation, Inc.
 #
 # This file is part of GNU Radio
 #
@@ -141,6 +141,9 @@ class UHDApp(object):
         if args.spec:
             for mb_idx in xrange(self.usrp.get_num_mboards()):
                 self.usrp.set_subdev_spec(args.spec, mb_idx)
+        # Set the clock source:
+        if args.clock_source is not None:
+            self.usrp.set_clock_source(args.clock_source)
         # Sampling rate:
         self.usrp.set_samp_rate(args.samp_rate)
         self.samp_rate = self.usrp.get_samp_rate()
@@ -305,5 +308,7 @@ class UHDApp(object):
                             help="Show asynchronous message notifications from UHD")
         group.add_argument("--sync", choices=('default', 'pps', 'auto'),
                           default='auto', help="Set to 'pps' to sync devices to PPS")
+        group.add_argument("--clock-source",
+                          help="Set the clock source; typically 'internal', 'external' or 'gpsdo'")
         return parser
 
diff --git a/gr-uhd/examples/python/fm_tx4.py b/gr-uhd/examples/python/fm_tx4.py
index fefa67861b..516033dae1 100755
--- a/gr-uhd/examples/python/fm_tx4.py
+++ b/gr-uhd/examples/python/fm_tx4.py
@@ -63,7 +63,8 @@ class pipeline(gr.hier_block2):
             sys.exit(1)
 
         print audio_rate, if_rate
-        fmtx = analog.nbfm_tx(audio_rate, if_rate, max_dev=5e3, tau=75e-6)
+        fmtx = analog.nbfm_tx(audio_rate, if_rate, max_dev=5e3,
+	                      tau=75e-6, fh=0.925*if_rate/2.0)
 
         # Local oscillator
         lo = analog.sig_source_c(if_rate,            # sample rate
diff --git a/gr-uhd/include/gnuradio/uhd/usrp_source.h b/gr-uhd/include/gnuradio/uhd/usrp_source.h
index 19b3feb61f..19201c031c 100644
--- a/gr-uhd/include/gnuradio/uhd/usrp_source.h
+++ b/gr-uhd/include/gnuradio/uhd/usrp_source.h
@@ -96,10 +96,13 @@ namespace gr {
       /*!
        * \param device_addr the address to identify the hardware
        * \param stream_args the IO format and channel specification
+       * \param issue_stream_cmd_on_start enable or disable continuous streaming when flowgraph
+       *   starts (default true)
        * \return a new USRP source block object
        */
       static sptr make(const ::uhd::device_addr_t &device_addr,
-                       const ::uhd::stream_args_t &stream_args);
+                       const ::uhd::stream_args_t &stream_args,
+                       const bool issue_stream_cmd_on_start = true);
 
       /*!
        * Set the start time for incoming samples.
diff --git a/gr-uhd/lib/usrp_source_impl.cc b/gr-uhd/lib/usrp_source_impl.cc
index eeb9521a5a..7ad2280955 100644
--- a/gr-uhd/lib/usrp_source_impl.cc
+++ b/gr-uhd/lib/usrp_source_impl.cc
@@ -53,20 +53,23 @@ namespace gr {
 
     usrp_source::sptr
     usrp_source::make(const ::uhd::device_addr_t &device_addr,
-                      const ::uhd::stream_args_t &stream_args)
+                      const ::uhd::stream_args_t &stream_args,
+                      const bool issue_stream_cmd_on_start)
     {
       check_abi();
       return usrp_source::sptr
-        (new usrp_source_impl(device_addr, stream_args_ensure(stream_args)));
+        (new usrp_source_impl(device_addr, stream_args_ensure(stream_args), issue_stream_cmd_on_start));
     }
 
     usrp_source_impl::usrp_source_impl(const ::uhd::device_addr_t &device_addr,
-                                       const ::uhd::stream_args_t &stream_args):
+                                       const ::uhd::stream_args_t &stream_args,
+                                       const bool issue_stream_cmd_on_start):
       usrp_block("gr uhd usrp source",
                     io_signature::make(0, 0, 0),
                     args_to_io_sig(stream_args)),
       usrp_block_impl(device_addr, stream_args, ""),
-      _tag_now(false)
+      _tag_now(false),
+      _issue_stream_cmd_on_start(issue_stream_cmd_on_start)
     {
       std::stringstream str;
       str << name() << unique_id();
@@ -382,18 +385,20 @@ namespace gr {
         _samps_per_packet = _rx_stream->get_max_num_samps();
       }
 #endif
-      //setup a stream command that starts streaming slightly in the future
-      static const double reasonable_delay = 0.1; //order of magnitude over RTT
-      ::uhd::stream_cmd_t stream_cmd(::uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);
-      stream_cmd.stream_now = _stream_now;
-      if(_start_time_set) {
-        _start_time_set = false; //cleared for next run
-        stream_cmd.time_spec = _start_time;
-      }
-      else {
-        stream_cmd.time_spec = get_time_now() + ::uhd::time_spec_t(reasonable_delay);
+      if(_issue_stream_cmd_on_start){
+        //setup a stream command that starts streaming slightly in the future
+        static const double reasonable_delay = 0.1; //order of magnitude over RTT
+        ::uhd::stream_cmd_t stream_cmd(::uhd::stream_cmd_t::STREAM_MODE_START_CONTINUOUS);
+        stream_cmd.stream_now = _stream_now;
+        if(_start_time_set) {
+          _start_time_set = false; //cleared for next run
+          stream_cmd.time_spec = _start_time;
+        }
+        else {
+          stream_cmd.time_spec = get_time_now() + ::uhd::time_spec_t(reasonable_delay);
+        }
+        this->issue_stream_cmd(stream_cmd);
       }
-      this->issue_stream_cmd(stream_cmd);
       _tag_now = true;
       return true;
     }
diff --git a/gr-uhd/lib/usrp_source_impl.h b/gr-uhd/lib/usrp_source_impl.h
index 98af816c02..b43df4dab3 100644
--- a/gr-uhd/lib/usrp_source_impl.h
+++ b/gr-uhd/lib/usrp_source_impl.h
@@ -55,7 +55,8 @@ namespace gr {
     {
     public:
       usrp_source_impl(const ::uhd::device_addr_t &device_addr,
-                       const ::uhd::stream_args_t &stream_args);
+                       const ::uhd::stream_args_t &stream_args,
+                       const bool issue_stream_cmd_on_start = true);
       ~usrp_source_impl();
 
       // Get Commands
@@ -119,6 +120,7 @@ namespace gr {
       bool _tag_now;
       ::uhd::rx_metadata_t _metadata;
       pmt::pmt_t _id;
+      bool _issue_stream_cmd_on_start;
 
       //tag shadows
       double _samp_rate;