multi_usrp: Factor out make_overall_tune_range() and fix limits

This function had an issue where it might return negative frequency
values. A quick fix was to limit it to positive frequencies.

Since this function was duplicated between multi_usrp and
multi_usrp_rfnoc, this patch also moves it to a common location to not
have to fix it twice.

3 files changed, 39 insertions, 42 deletions

diff --git a/host/lib/include/uhdlib/usrp/multi_usrp_utils.hpp b/host/lib/include/uhdlib/usrp/multi_usrp_utils.hpp
new file mode 100644
index 000000000..40c360339
--- /dev/null
+++ b/host/lib/include/uhdlib/usrp/multi_usrp_utils.hpp
@@ -0,0 +1,37 @@
+//
+// Copyright 2021 Ettus Research, a National Instruments Brand
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+//
+
+#pragma once
+
+#include <uhd/types/ranges.hpp>
+
+namespace uhd {
+
+/*! Create a total tune range for multi_usrp objects
+ *
+ * Digital tuning can be used to shift the baseband below / past the tunable
+ * limits of the actual RF front-end. The baseband filter, located on the
+ * daughterboard, however, limits the useful instantaneous bandwidth. We
+ * allow the user to tune to the edge of the filter, where the roll-off
+ * begins.  This prevents the user from tuning past the point where less
+ * than half of the spectrum would be useful.
+ * Also, we make sure that frequencies don't become negative.
+ */
+static meta_range_t make_overall_tune_range(
+    const meta_range_t& fe_range, const meta_range_t& dsp_range, const double bw)
+{
+    meta_range_t range;
+    for (const range_t& sub_range : fe_range) {
+        range.push_back(range_t(
+            std::max(0.0, sub_range.start() + std::max(dsp_range.start(), -bw / 2)),
+            sub_range.stop() + std::min(dsp_range.stop(), bw / 2),
+            dsp_range.step()));
+    }
+    return range;
+}
+
+
+} // namespace uhd
diff --git a/host/lib/usrp/multi_usrp.cpp b/host/lib/usrp/multi_usrp.cpp
index bb5b9e5fc..048db0d35 100644
--- a/host/lib/usrp/multi_usrp.cpp
+++ b/host/lib/usrp/multi_usrp.cpp
@@ -21,6 +21,7 @@
 #include <uhd/utils/soft_register.hpp>
 #include <uhdlib/rfnoc/rfnoc_device.hpp>
 #include <uhdlib/usrp/gpio_defs.hpp>
+#include <uhdlib/usrp/multi_usrp_utils.hpp>
 #include <boost/algorithm/string.hpp>
 #include <boost/assign/list_of.hpp>
 #include <boost/format.hpp>
@@ -190,25 +191,6 @@ clipped:\n" "    Target Frequency: %f MHz\n" "    Clipped Target Frequency: %f M
     }
 }*/
 
-/*! The CORDIC can be used to shift the baseband below / past the tunable
- * limits of the actual RF front-end. The baseband filter, located on the
- * daughterboard, however, limits the useful instantaneous bandwidth. We
- * allow the user to tune to the edge of the filter, where the roll-off
- * begins.  This prevents the user from tuning past the point where less
- * than half of the spectrum would be useful. */
-static meta_range_t make_overall_tune_range(
-    const meta_range_t& fe_range, const meta_range_t& dsp_range, const double bw)
-{
-    meta_range_t range;
-    for (const range_t& sub_range : fe_range) {
-        range.push_back(range_t(sub_range.start() + std::max(dsp_range.start(), -bw / 2),
-            sub_range.stop() + std::min(dsp_range.stop(), bw / 2),
-            dsp_range.step()));
-    }
-    return range;
-}
-
-
 /***********************************************************************
  * Gain helper functions
  **********************************************************************/
diff --git a/host/lib/usrp/multi_usrp_rfnoc.cpp b/host/lib/usrp/multi_usrp_rfnoc.cpp
index f87e52190..8a11be122 100644
--- a/host/lib/usrp/multi_usrp_rfnoc.cpp
+++ b/host/lib/usrp/multi_usrp_rfnoc.cpp
@@ -18,6 +18,7 @@
 #include <uhdlib/rfnoc/rfnoc_rx_streamer.hpp>
 #include <uhdlib/rfnoc/rfnoc_tx_streamer.hpp>
 #include <uhdlib/usrp/gpio_defs.hpp>
+#include <uhdlib/usrp/multi_usrp_utils.hpp>
 #include <uhdlib/utils/narrow.hpp>
 #include <unordered_set>
 #include <boost/format.hpp>
@@ -441,29 +442,6 @@ public:
     }
 
 
-    /***********************************************************************
-     * Helper methods
-     **********************************************************************/
-    /*! The CORDIC can be used to shift the baseband below / past the tunable
-     * limits of the actual RF front-end. The baseband filter, located on the
-     * daughterboard, however, limits the useful instantaneous bandwidth. We
-     * allow the user to tune to the edge of the filter, where the roll-off
-     * begins.  This prevents the user from tuning past the point where less
-     * than half of the spectrum would be useful.
-     */
-    static meta_range_t make_overall_tune_range(
-        const meta_range_t& fe_range, const meta_range_t& dsp_range, const double bw)
-    {
-        meta_range_t range;
-        for (const range_t& sub_range : fe_range) {
-            range.push_back(
-                range_t(sub_range.start() + std::max(dsp_range.start(), -bw / 2),
-                    sub_range.stop() + std::min(dsp_range.stop(), bw / 2),
-                    dsp_range.step()));
-        }
-        return range;
-    }
-
     dict<std::string, std::string> get_usrp_rx_info(size_t chan) override
     {
         auto& rx_chain      = _get_rx_chan(chan);