rfnoc: Add MTU property to TX streamer

2 files changed, 34 insertions, 5 deletions

diff --git a/host/lib/include/uhdlib/rfnoc/rfnoc_tx_streamer.hpp b/host/lib/include/uhdlib/rfnoc/rfnoc_tx_streamer.hpp
index 4acee45cc..3bfc9d05a 100644
--- a/host/lib/include/uhdlib/rfnoc/rfnoc_tx_streamer.hpp
+++ b/host/lib/include/uhdlib/rfnoc/rfnoc_tx_streamer.hpp
@@ -69,6 +69,15 @@ public:
     bool check_topology(const std::vector<size_t>& connected_inputs,
         const std::vector<size_t>& connected_outputs);
 
+    /*! Connects a channel to the streamer port
+     *
+     * Overrides method in tx_streamer_impl.
+     *
+     * \param channel The streamer channel to which to connect
+     * \param xport The transport for the specified channel
+     */
+    void connect_channel(const size_t channel, chdr_tx_data_xport::uptr xport);
+
 private:
     void _register_props(const size_t chan, const std::string& otw_format);
 
@@ -77,6 +86,7 @@ private:
     std::vector<property_t<double>> _samp_rate_out;
     std::vector<property_t<double>> _tick_rate_out;
     std::vector<property_t<std::string>> _type_out;
+    std::vector<property_t<size_t>> _mtu_out;
 
     // Streamer unique ID
     const std::string _unique_id;
diff --git a/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp b/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp
index 60881dad2..819ed5558 100644
--- a/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp
+++ b/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp
@@ -79,14 +79,14 @@ public:
         _spp = stream_args.args.cast<size_t>("spp", _spp);
     }
 
-    void connect_channel(const size_t channel, typename transport_t::uptr xport)
+    virtual void connect_channel(const size_t channel, typename transport_t::uptr xport)
     {
-        const size_t max_pyld_size = xport->get_max_payload_size();
+        const size_t mtu = xport->get_max_payload_size();
         _zero_copy_streamer.connect_channel(channel, std::move(xport));
 
-        // Set spp based on the transport frame size
-        const size_t xport_spp = max_pyld_size / _convert_info.bytes_per_otw_item;
-        _spp                   = std::min(_spp, xport_spp);
+        if (mtu < _mtu) {
+            set_mtu(mtu);
+        }
     }
 
     size_t get_num_channels() const
@@ -187,6 +187,22 @@ public:
     }
 
 protected:
+    //! Returns the size in bytes of a sample in a packet
+    size_t get_mtu() const
+    {
+        return _mtu;
+    }
+
+    //! Sets the MTU and calculates spp
+    void set_mtu(const size_t mtu)
+    {
+        _mtu = mtu;
+
+        // Check if spp needs to be lowered. SPP may already be lower than the
+        // value allowed by mtu if the user specified it using stream_args.
+        _spp = std::min(_spp, _mtu / _convert_info.bytes_per_otw_item);
+    }
+
     //! Configures scaling factor for conversion
     void set_scale_factor(const size_t chan, const double scale_factor)
     {
@@ -295,6 +311,9 @@ private:
     // Sample rate used to calculate metadata time_spec_t
     double _samp_rate = 1.0;
 
+    // Maximum payload size
+    size_t _mtu = std::numeric_limits<std::size_t>::max();
+
     // Maximum number of samples per packet
     size_t _spp = std::numeric_limits<std::size_t>::max();