python: Add block controller factory utility

This commit adds a utility class for use with the Python RFNoC block
controller PyBind bindings which facilitates constructing instances of a
specific block controller type from its noc_block_base base class. This
allows Python code to create and configure specific block controller
instances by calling get_block on a uhd.rfnoc.RfnocGraph object with the
block ID of the block in question and then passing the result into the
constructor method of the block controller, e.g.:

    graph = uhd.rfnoc.RfnocGraph("addr=...")
    block = graph.get_block(uhd.rfnoc.BlockID("0/DDC#0"))
    ddc = uhd.rfnoc.DdcBlockControl(block)
    ddc.set_input_rate(10e6, 0)

1 files changed, 30 insertions, 0 deletions

diff --git a/host/lib/rfnoc/block_controller_factory_python.hpp b/host/lib/rfnoc/block_controller_factory_python.hpp
new file mode 100644
index 000000000..2eda892dd
--- /dev/null
+++ b/host/lib/rfnoc/block_controller_factory_python.hpp
@@ -0,0 +1,30 @@
+//
+// Copyright 2020 Ettus Research, a National Instruments Brand
+//
+// SPDX-License-Identifier: GPL-3.0-or-laster
+//
+
+#pragma once
+
+#include <uhd/rfnoc/noc_block_base.hpp>
+
+using namespace uhd::rfnoc;
+
+namespace {
+
+// Static factory for constructing a block controller T given an instance of
+// the superclass noc_block_base for the block controller, as might be
+// returned from uhd::rfnoc::graph::get_block(). The instance is downcast to
+// the derived class and returned to the client as a T::sptr. If block_base
+// does not represent an instance of T, nullptr is returned.
+template <typename T>
+class block_controller_factory
+{
+public:
+    static typename T::sptr make_from(noc_block_base::sptr block_base)
+    {
+        return std::dynamic_pointer_cast<T>(block_base);
+    }
+};
+
+} // namespace