2 files changed, 39 insertions, 5 deletions

diff --git a/gr-uhd/lib/gr_uhd_usrp_sink.cc b/gr-uhd/lib/gr_uhd_usrp_sink.cc
index 05237100c..5d8d235a1 100644
--- a/gr-uhd/lib/gr_uhd_usrp_sink.cc
+++ b/gr-uhd/lib/gr_uhd_usrp_sink.cc
@@ -56,7 +56,9 @@ public:
             gr_make_io_signature(0, 0, 0)
         ),
         _stream_args(stream_args),
-        _nchan(std::max<size_t>(1, stream_args.channels.size()))
+        _nchan(std::max<size_t>(1, stream_args.channels.size())),
+        _stream_now(_nchan == 1),
+        _start_time_set(false)
     {
         if (stream_args.cpu_format == "fc32") _type = boost::make_shared<uhd::io_type_t>(uhd::io_type_t::COMPLEX_FLOAT32);
         if (stream_args.cpu_format == "sc16") _type = boost::make_shared<uhd::io_type_t>(uhd::io_type_t::COMPLEX_INT16);
@@ -372,6 +374,12 @@ public:
         }
     }
 
+    void set_start_time(const uhd::time_spec_t &time){
+        _start_time = time;
+        _start_time_set = true;
+        _stream_now = false;
+    }
+
     //Send an empty start-of-burst packet to begin streaming.
     //Set at a time in the near future to avoid late packets.
     bool start(void){
@@ -381,8 +389,14 @@ public:
 
         _metadata.start_of_burst = true;
         _metadata.end_of_burst = false;
-        _metadata.has_time_spec = _nchan > 1;
-        _metadata.time_spec = get_time_now() + uhd::time_spec_t(0.01);
+        _metadata.has_time_spec = not _stream_now;
+        if (_start_time_set){
+            _start_time_set = false; //cleared for next run
+            _metadata.time_spec = _start_time;
+        }
+        else{
+            _metadata.time_spec = get_time_now() + uhd::time_spec_t(0.01);
+        }
 
         #ifdef GR_UHD_USE_STREAM_API
         _tx_stream->send(
@@ -423,9 +437,13 @@ private:
     uhd::tx_streamer::sptr _tx_stream;
     #endif
     size_t _nchan;
+    bool _stream_now;
     uhd::tx_metadata_t _metadata;
     double _sample_rate;
 
+    uhd::time_spec_t _start_time;
+    bool _start_time_set;
+
     //stream tags related stuff
     std::vector<gr_tag_t> _tags;
 };
diff --git a/gr-uhd/lib/gr_uhd_usrp_source.cc b/gr-uhd/lib/gr_uhd_usrp_source.cc
index 33596e37b..e52782847 100644
--- a/gr-uhd/lib/gr_uhd_usrp_source.cc
+++ b/gr-uhd/lib/gr_uhd_usrp_source.cc
@@ -58,7 +58,8 @@ public:
         _stream_args(stream_args),
         _nchan(std::max<size_t>(1, stream_args.channels.size())),
         _stream_now(_nchan == 1),
-        _tag_now(false)
+        _tag_now(false),
+        _start_time_set(false)
     {
         if (stream_args.cpu_format == "fc32") _type = boost::make_shared<uhd::io_type_t>(uhd::io_type_t::COMPLEX_FLOAT32);
         if (stream_args.cpu_format == "sc16") _type = boost::make_shared<uhd::io_type_t>(uhd::io_type_t::COMPLEX_INT16);
@@ -363,6 +364,12 @@ public:
         return num_samps;
     }
 
+    void set_start_time(const uhd::time_spec_t &time){
+        _start_time = time;
+        _start_time_set = true;
+        _stream_now = false;
+    }
+
     bool start(void){
         #ifdef GR_UHD_USE_STREAM_API
         _rx_stream = _dev->get_rx_stream(_stream_args);
@@ -372,7 +379,13 @@ public:
         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;
-        stream_cmd.time_spec = get_time_now() + uhd::time_spec_t(reasonable_delay);
+        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);
+        }
         _dev->issue_stream_cmd(stream_cmd);
         _tag_now = true;
         return true;
@@ -468,6 +481,9 @@ private:
     bool _stream_now, _tag_now;
     uhd::rx_metadata_t _metadata;
     pmt::pmt_t _id;
+
+    uhd::time_spec_t _start_time;
+    bool _start_time_set;
 };