5 files changed, 50 insertions, 12 deletions
diff --git a/host/lib/usrp/mpmd/mpmd_impl.cpp b/host/lib/usrp/mpmd/mpmd_impl.cpp
index 911b57558..7b4ca5bc8 100644
--- a/host/lib/usrp/mpmd/mpmd_impl.cpp
+++ b/host/lib/usrp/mpmd/mpmd_impl.cpp
@@ -204,6 +204,25 @@ namespace {
             ;
         }
 
+        /*** MTUs ***********************************************************/
+        tree->create<size_t>(mb_path / "mtu/recv")
+            .add_coerced_subscriber([](const size_t){
+                throw uhd::runtime_error(
+                    "Attempting to write read-only value (MTU)!");
+            })
+            .set_publisher([mb](){
+                return mb->get_mtu(uhd::RX_DIRECTION);
+            })
+        ;
+        tree->create<size_t>(mb_path / "mtu/send")
+            .add_coerced_subscriber([](const size_t){
+                throw uhd::runtime_error(
+                    "Attempting to write read-only value (MTU)!");
+            })
+            .set_publisher([mb](){
+                return mb->get_mtu(uhd::TX_DIRECTION);
+            })
+        ;
     }
 
     void reset_time_synchronized(uhd::property_tree::sptr tree)
@@ -389,20 +408,8 @@ mpmd_mboard_impl::uptr mpmd_impl::setup_mb(
     _tree->create<std::string>(mb_path / "connection")
         .set(mb->device_info.get("connection", "remote"));
 
-    // Do real MTU discovery (something similar like X300 but with MPM)
-
-    _tree->create<size_t>(mb_path / "mtu/recv").set(1500);
-    _tree->create<size_t>(mb_path / "mtu/send").set(1500);
     _tree->create<size_t>(mb_path / "link_max_rate").set(1e9 / 8);
 
-    // query more information about FPGA/MPM
-
-
-    // Query time/clock sources on mboards/dboards
-    // Throw rpc calls with boost bind into the property tree?
-
-
-    // implicit move
     return mb;
 }
 
diff --git a/host/lib/usrp/mpmd/mpmd_impl.hpp b/host/lib/usrp/mpmd/mpmd_impl.hpp
index fe98b0329..50f533c99 100644
--- a/host/lib/usrp/mpmd/mpmd_impl.hpp
+++ b/host/lib/usrp/mpmd/mpmd_impl.hpp
@@ -100,6 +100,8 @@ class mpmd_mboard_impl
         const uhd::device_addr_t& args
     );
 
+    size_t get_mtu(const uhd::direction_t dir) const;
+
 
     uhd::device_addr_t get_rx_hints() const;
     uhd::device_addr_t get_tx_hints() const;
diff --git a/host/lib/usrp/mpmd/mpmd_mboard_impl.cpp b/host/lib/usrp/mpmd/mpmd_mboard_impl.cpp
index 1038be26d..501f7f701 100644
--- a/host/lib/usrp/mpmd/mpmd_mboard_impl.cpp
+++ b/host/lib/usrp/mpmd/mpmd_mboard_impl.cpp
@@ -194,6 +194,11 @@ uhd::both_xports_t mpmd_mboard_impl::make_transport(
     return xports;
 }
 
+size_t mpmd_mboard_impl::get_mtu(const uhd::direction_t dir) const
+{
+    return _xport_mgr->get_mtu(dir);
+}
+
 uhd::device_addr_t mpmd_mboard_impl::get_rx_hints() const
 {
     // TODO: See if we need to do anything here. get_rx_stream() might care.
diff --git a/host/lib/usrp/mpmd/mpmd_xport_mgr.cpp b/host/lib/usrp/mpmd/mpmd_xport_mgr.cpp
index 0ca77c740..3d999c1ad 100644
--- a/host/lib/usrp/mpmd/mpmd_xport_mgr.cpp
+++ b/host/lib/usrp/mpmd/mpmd_xport_mgr.cpp
@@ -68,6 +68,24 @@ public:
        );
     }
 
+    size_t get_mtu(
+        const uhd::direction_t dir
+    ) const {
+        if (_xport_ctrls.empty()) {
+            UHD_LOG_WARNING("MPMD",
+                "Cannot determine MTU, no transport controls have been "
+                "established!");
+            return 0;
+        }
+
+        size_t mtu = ~size_t(0);
+        for (const auto &xport_ctrl_pair : _xport_ctrls) {
+            mtu = std::min(mtu, xport_ctrl_pair.second->get_mtu(dir));
+        }
+
+        return mtu;
+    }
+
 
 private:
     /**************************************************************************
diff --git a/host/lib/usrp/mpmd/mpmd_xport_mgr.hpp b/host/lib/usrp/mpmd/mpmd_xport_mgr.hpp
index cdb082111..44906c872 100644
--- a/host/lib/usrp/mpmd/mpmd_xport_mgr.hpp
+++ b/host/lib/usrp/mpmd/mpmd_xport_mgr.hpp
@@ -99,6 +99,12 @@ public:
         const uhd::device_addr_t& xport_args,
         xport_info_t& xport_info_out
     ) = 0;
+
+    /*! Return the path MTU for whatever this manager lets us do
+     */
+    virtual size_t get_mtu(
+        const uhd::direction_t dir
+    ) const = 0;
 };
 
 }}} /* namespace uhd::mpmd::xport */