gr-usrp2: implement start_streaming_at(usrp2::fpga_timestamp time)

This new method on usrp2.sink_* causes the first TX sample data to be
sent at the FPGA clock time specified, with all further data immediately
following.

u = usrp2.sink_32fc() # or 16sc
...configure sink here...
u.sync_to_pps()
...delay a second for PPS to have happened
u.start_streaming_at(int(100e6)) # start TX stream one second later
...start flowgraph here...

If this function is not called, all transmit data will be sent
immediately (the prior behavior).

1 files changed, 8 insertions, 0 deletions

diff --git a/gr-usrp2/src/usrp2_sink_base.h b/gr-usrp2/src/usrp2_sink_base.h
index 38dc4f236..d831d4df6 100644
--- a/gr-usrp2/src/usrp2_sink_base.h
+++ b/gr-usrp2/src/usrp2_sink_base.h
@@ -37,6 +37,9 @@ protected:
 		  const std::string &mac)
     throw (std::runtime_error);
 
+  bool d_should_wait;
+  usrp2::fpga_timestamp d_tx_time;
+
 public:
   ~usrp2_sink_base();
 
@@ -139,6 +142,11 @@ public:
    * \brief Read daughterboard GPIO pin values
    */
   bool read_gpio(uint16_t *value);
+
+  /*!
+   * \brief First samples begin streaming to USRP2 at given time
+   */
+  bool start_streaming_at(usrp2::fpga_timestamp time);
 };
 
 #endif /* INCLUDED_USRP2_SINK_BASE_H */