rfnoc: Add MTU property to RX streamer

2 files changed, 34 insertions, 12 deletions

diff --git a/host/lib/include/uhdlib/transport/rx_streamer_impl.hpp b/host/lib/include/uhdlib/transport/rx_streamer_impl.hpp
index cc989e8f2..b52358e55 100644
--- a/host/lib/include/uhdlib/transport/rx_streamer_impl.hpp
+++ b/host/lib/include/uhdlib/transport/rx_streamer_impl.hpp
@@ -87,18 +87,23 @@ public:
         _setup_converters(num_ports, stream_args);
         _zero_copy_streamer.set_samp_rate(_samp_rate);
         _zero_copy_streamer.set_bytes_per_item(_convert_info.bytes_per_otw_item);
+
+        if (stream_args.args.has_key("spp")) {
+            _spp = stream_args.args.cast<size_t>("spp", _spp);
+            _mtu = _spp * _convert_info.bytes_per_otw_item;
+        }
     }
 
     //! Connect a new channel to the streamer
     // FIXME: Needs some way to handle virtual channels, since xport could be shared among them
-    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);
+        }
     }
 
     //! Implementation of rx_streamer API method
@@ -183,6 +188,19 @@ protected:
         _converters[chan]->set_scalar(scale_factor);
     }
 
+    //! Returns the maximum payload size
+    size_t get_mtu() const
+    {
+        return _mtu;
+    }
+
+    //! Sets the MTU and calculates spp
+    void set_mtu(const size_t mtu)
+    {
+        _mtu = mtu;
+        _spp = _mtu / _convert_info.bytes_per_otw_item;
+    }
+
     //! Configures sample rate for conversion of timestamp
     void set_samp_rate(const double rate)
     {
@@ -336,6 +354,9 @@ private:
     // Sample rate used to calculate metadata time_spec_t
     double _samp_rate = 1.0;
 
+    // MTU, determined when xport is connected and modifiable by subclass
+    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();
 
diff --git a/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp b/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp
index 35a724fa9..fa84026fe 100644
--- a/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp
+++ b/host/lib/include/uhdlib/transport/tx_streamer_impl.hpp
@@ -76,7 +76,11 @@ public:
     {
         _setup_converters(num_chans, stream_args);
         _zero_copy_streamer.set_bytes_per_item(_convert_info.bytes_per_otw_item);
-        _spp = stream_args.args.cast<size_t>("spp", _spp);
+
+        if (stream_args.args.has_key("spp")) {
+            _spp = stream_args.args.cast<size_t>("spp", _spp);
+            _mtu = _spp * _convert_info.bytes_per_otw_item;
+        }
     }
 
     virtual void connect_channel(const size_t channel, typename transport_t::uptr xport)
@@ -184,7 +188,7 @@ protected:
         return _zero_copy_streamer.get_tick_rate();
     }
 
-    //! Returns the size in bytes of a sample in a packet
+    //! Returns the maximum payload size
     size_t get_mtu() const
     {
         return _mtu;
@@ -194,10 +198,7 @@ protected:
     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);
+        _spp = _mtu / _convert_info.bytes_per_otw_item;
     }
 
     //! Configures scaling factor for conversion
@@ -308,7 +309,7 @@ private:
     // Sample rate used to calculate metadata time_spec_t
     double _samp_rate = 1.0;
 
-    // Maximum payload size
+    // MTU, determined when xport is connected and modifiable by subclass
     size_t _mtu = std::numeric_limits<std::size_t>::max();
 
     // Maximum number of samples per packet