rfnoc: radio: Introduce coerce_rate() method

This is a helper method for property resolution, where set_rate() is not
appropriate.

2 files changed, 24 insertions, 3 deletions

diff --git a/host/lib/include/uhdlib/rfnoc/radio_control_impl.hpp b/host/lib/include/uhdlib/rfnoc/radio_control_impl.hpp
index 6b50cc31c..fc90035f7 100644
--- a/host/lib/include/uhdlib/rfnoc/radio_control_impl.hpp
+++ b/host/lib/include/uhdlib/rfnoc/radio_control_impl.hpp
@@ -256,6 +256,22 @@ public:
     static const uhd::fs_path FE_PATH;
 
 protected:
+    /*! Helper function for property propagation: Like set_rate(), but called
+     * during a different context.
+     *
+     * This function is called from the samp_rate property resolver. The
+     * difference to set_rate() is that the latter is a user API, and may
+     * trigger different kinds of warnings or errors.
+     * If the radio supports changing its sampling rate at runtime, it is OK to
+     * call set_rate() within this function.
+     *
+     * Default implementation is to simply return the current rate.
+     */
+    virtual double coerce_rate(const double /* rate */)
+    {
+        return _rate;
+    }
+
     //! Properties for samp_rate (one per port)
     std::vector<property_t<double>> _samp_rate_in;
     //! Properties for samp_rate (one per port)
diff --git a/host/lib/rfnoc/radio_control_impl.cpp b/host/lib/rfnoc/radio_control_impl.cpp
index f71c73289..9648b5dbf 100644
--- a/host/lib/rfnoc/radio_control_impl.cpp
+++ b/host/lib/rfnoc/radio_control_impl.cpp
@@ -175,9 +175,12 @@ radio_control_impl::radio_control_impl(make_args_ptr make_args)
             {&_spp_prop.back()},
             [this, chan, &spp = _spp_prop.back()]() {
                 RFNOC_LOG_TRACE("Calling resolver for spp@" << chan);
+                // TODO: Replace the magic number 16 (the protocol overhead)
+                // with something else that is calculated based on the CHDR width
                 const int mtu =
-                    static_cast<int>(get_mtu({res_source_info::OUTPUT_EDGE, chan}));
-                const int max_spp_per_mtu = mtu / (_samp_width / 8) - (mtu % _spc);
+                    static_cast<int>(get_mtu({res_source_info::OUTPUT_EDGE, chan})) - 16;
+                const int mtu_samps       = mtu / (_samp_width / 8);
+                const int max_spp_per_mtu = mtu_samps - (mtu_samps % _spc);
                 if (spp.get() > max_spp_per_mtu) {
                     RFNOC_LOG_WARNING("spp value " << spp.get() << " exceeds MTU of "
                                                    << mtu << "! Coercing to "
@@ -196,13 +199,15 @@ radio_control_impl::radio_control_impl(make_args_ptr make_args)
                         "spp must be greater than zero! Coercing to " << spp.get());
                 }
             });
+        // Note: The following resolver calls coerce_rate(), which is virtual.
+        // At run time, it will use the implementation by the child class.
         add_property_resolver({&_samp_rate_in.back(), &_samp_rate_out.back()},
             {&_samp_rate_in.back(), &_samp_rate_out.back()},
             [this, chan,
                 &samp_rate_in  = _samp_rate_in.at(chan),
                 &samp_rate_out = _samp_rate_out.at(chan)]() {
                 RFNOC_LOG_TRACE("Calling resolver for samp_rate@" << chan);
-                samp_rate_in = set_rate(samp_rate_in.get());
+                samp_rate_in  = coerce_rate(samp_rate_in.get());
                 samp_rate_out = samp_rate_in.get();
             });
         // Resolvers for type: These are constants