6 files changed, 22 insertions, 1 deletions
diff --git a/host/include/uhd/stream.hpp b/host/include/uhd/stream.hpp
index 8f3219dbd..b41c1733d 100644
--- a/host/include/uhd/stream.hpp
+++ b/host/include/uhd/stream.hpp
@@ -78,10 +78,16 @@ struct UHD_API stream_args_t{
     /*!
      * The args parameter is used to pass arbitrary key/value pairs.
      * Possible keys used by args (depends on implementation):
+     *
      * - scalar: an integer scaling factor used with the sc8 wire format.
      * The key/value pair scalar=1024 means that the sample in the DSP
      * was multiplied by 1024 before its upper 8 bits were harvested.
      *
+     * - underflow_policy: how the TX DSP should recover from underflow.
+     * Possible options are "next_burst" or "next_packet".
+     * In the "next_burst" mode, the DSP drops incoming packets until a new burst is started.
+     * In the "next_packet" mode, the DSP starts transmitting again at the next packet.
+     *
      * The following are not implemented, but are listed for conceptual purposes:
      * - function: magnitude or phase/magnitude
      * - units: numeric units like counts or dBm
diff --git a/host/lib/usrp/b100/io_impl.cpp b/host/lib/usrp/b100/io_impl.cpp
index 5b2fa4686..7e4cd6f8e 100644
--- a/host/lib/usrp/b100/io_impl.cpp
+++ b/host/lib/usrp/b100/io_impl.cpp
@@ -291,6 +291,7 @@ tx_streamer::sptr b100_impl::get_tx_stream(const uhd::stream_args_t &args_){
         const size_t dsp = args.channels[chan_i];
         UHD_ASSERT_THROW(dsp == 0); //always 0
         if (not args.args.has_key("noclear")) _tx_dsp->clear();
+        if (args.args.has_key("underflow_policy")) _tx_dsp->set_underflow_policy(args.args["underflow_policy"]);
         my_streamer->set_xport_chan_get_buff(chan_i, boost::bind(
             &zero_copy_if::get_send_buff, _data_transport, _1
         ));
diff --git a/host/lib/usrp/cores/tx_dsp_core_200.cpp b/host/lib/usrp/cores/tx_dsp_core_200.cpp
index 4e1a3e44d..c5de4e361 100644
--- a/host/lib/usrp/cores/tx_dsp_core_200.cpp
+++ b/host/lib/usrp/cores/tx_dsp_core_200.cpp
@@ -60,13 +60,23 @@ public:
     {
         //init the tx control registers
         this->clear();
+        this->set_underflow_policy("next_packet");
     }
 
     void clear(void){
         _iface->poke32(REG_TX_CTRL_CLEAR_STATE, 1); //reset
         _iface->poke32(REG_TX_CTRL_NUM_CHAN, 0);    //1 channel
         _iface->poke32(REG_TX_CTRL_REPORT_SID, _sid);
-        _iface->poke32(REG_TX_CTRL_POLICY, FLAG_TX_CTRL_POLICY_NEXT_PACKET);
+    }
+
+    void set_underflow_policy(const std::string &policy){
+        if (policy == "next_packet"){
+            _iface->poke32(REG_TX_CTRL_POLICY, FLAG_TX_CTRL_POLICY_NEXT_PACKET);
+        }
+        else if (policy == "next_burst"){
+            _iface->poke32(REG_TX_CTRL_POLICY, FLAG_TX_CTRL_POLICY_NEXT_BURST);
+        }
+        else throw uhd::value_error("USRP TX cannot handle requested underflow policy: " + policy);
     }
 
     void set_tick_rate(const double rate){
diff --git a/host/lib/usrp/cores/tx_dsp_core_200.hpp b/host/lib/usrp/cores/tx_dsp_core_200.hpp
index 50d128df4..4b39a5b07 100644
--- a/host/lib/usrp/cores/tx_dsp_core_200.hpp
+++ b/host/lib/usrp/cores/tx_dsp_core_200.hpp
@@ -50,6 +50,8 @@ public:
 
     virtual void set_updates(const size_t cycles_per_up, const size_t packets_per_up) = 0;
 
+    virtual void set_underflow_policy(const std::string &policy) = 0;
+
 };
 
 #endif /* INCLUDED_LIBUHD_USRP_TX_DSP_CORE_200_HPP */
diff --git a/host/lib/usrp/e100/io_impl.cpp b/host/lib/usrp/e100/io_impl.cpp
index 5dddeef25..0cc09bd6d 100644
--- a/host/lib/usrp/e100/io_impl.cpp
+++ b/host/lib/usrp/e100/io_impl.cpp
@@ -367,6 +367,7 @@ tx_streamer::sptr e100_impl::get_tx_stream(const uhd::stream_args_t &args_){
         const size_t dsp = args.channels[chan_i];
         UHD_ASSERT_THROW(dsp == 0); //always 0
         if (not args.args.has_key("noclear")) _tx_dsp->clear();
+        if (args.args.has_key("underflow_policy")) _tx_dsp->set_underflow_policy(args.args["underflow_policy"]);
         my_streamer->set_xport_chan_get_buff(chan_i, boost::bind(
             &zero_copy_if::get_send_buff, _data_transport, _1
         ));
diff --git a/host/lib/usrp/usrp2/io_impl.cpp b/host/lib/usrp/usrp2/io_impl.cpp
index 62941ac79..44ab513ac 100644
--- a/host/lib/usrp/usrp2/io_impl.cpp
+++ b/host/lib/usrp/usrp2/io_impl.cpp
@@ -487,6 +487,7 @@ tx_streamer::sptr usrp2_impl::get_tx_stream(const uhd::stream_args_t &args_){
                     _mbc[mb].tx_dsp->clear();
                     _io_impl->fc_mons[abs]->clear();
                 }
+                if (args.args.has_key("underflow_policy")) _mbc[mb].tx_dsp->set_underflow_policy(args.args["underflow_policy"]);
                 my_streamer->set_xport_chan_get_buff(chan_i, boost::bind(
                     &usrp2_impl::io_impl::get_send_buff, _io_impl.get(), abs, _1
                 ));