multi_usrp_rfnoc: Manually pass sample rate to ddc/duc

This adds (and calls) methods to manually pass radio block sample rate
to the input/output properties of the ddc/duc during creation of the
multi_usrp_rfnoc object. The ddc/duc require this information in order
to return valid, possible output/input sample rates in
get_rx_rates()/get_tx_rates().

Before, the ddc/duc wouldn't have this rate until the rfnoc_graph had
been connected and committed, which happens in
get_rx_stream()/get_tx_stream(). Thus, this fixes an issue where a user
was unable to query possible sample rates prior to specifying a sample
rate and creating a stream.

host/include/uhd/rfnoc/ddc_block_control.hpp

@@ -89,6 +89,13 @@ public:
      */
     virtual double get_input_rate(const size_t chan) const = 0;
 
+    /*! Manually set the sampling rate at this block's input
+     *
+     * \param rate The requested rate
+     * \param chan The channel for which the rate is being set
+     */
+    virtual void set_input_rate(const double rate, const size_t chan) = 0;
+
     /*! Return the sampling rate at this block's output
      *
      * This is equivalent to calling get_input_rate() divided by the decimation.

host/include/uhd/rfnoc/duc_block_control.hpp

@@ -97,6 +97,13 @@ public:
      */
     virtual double get_output_rate(const size_t chan) const = 0;
 
+    /*! Manually set the sampling rate at this block's output
+     *
+     * \param rate The requested rate
+     * \param chan The channel for which the rate is being set
+     */
+    virtual void set_output_rate(const double rate, const size_t chan) = 0;
+
     /*! Return a range of valid input rates, based on the current output rate
      *
      * Note the return value is only valid as long as the output rate does not

host/lib/rfnoc/ddc_block_control.cpp

@@ -136,6 +136,11 @@ public:
         return _samp_rate_in.at(chan).is_valid() ? _samp_rate_in.at(chan).get() : 1.0;
     }
 
+    void set_input_rate(const double rate, const size_t chan)
+    {
+        set_property<double>("samp_rate", rate, {res_source_info::INPUT_EDGE, chan});
+    }
+
     double get_output_rate(const size_t chan) const
     {
         return _samp_rate_out.at(chan).is_valid() ? _samp_rate_out.at(chan).get() : 1.0;

host/lib/rfnoc/duc_block_control.cpp

@@ -138,6 +138,11 @@ public:
         return _samp_rate_out.at(chan).is_valid() ? _samp_rate_out.at(chan).get() : 1.0;
     }
 
+    void set_output_rate(const double rate, const size_t chan)
+    {
+        set_property<double>("samp_rate", rate, {res_source_info::OUTPUT_EDGE, chan});
+    }
+
     uhd::meta_range_t get_input_rates(const size_t chan) const
     {
         uhd::meta_range_t result;

host/lib/usrp/multi_usrp_rfnoc.cpp

@@ -214,6 +214,20 @@ public:
                 }
             }
         }
+        // Manually propagate radio block sample rates to DDC/DUC blocks in order to allow
+        // DDC/DUC blocks to have valid internal state before graph is (later) connected
+        for (size_t rx_chan = 0; rx_chan < get_rx_num_channels(); ++rx_chan) {
+            auto& rx_chain = _get_rx_chan(rx_chan);
+            if (rx_chain.ddc) {
+                rx_chain.ddc->set_input_rate(rx_chain.radio->get_rate(), rx_chain.block_chan);
+            }
+        }
+        for (size_t tx_chan = 0; tx_chan < get_tx_num_channels(); ++tx_chan) {
+            auto& tx_chain = _get_tx_chan(tx_chan);
+            if (tx_chain.duc) {
+                tx_chain.duc->set_output_rate(tx_chain.radio->get_rate(), tx_chain.block_chan);
+            }
+        }
         _graph->commit();
     }