multi_usrp: Add API call to query the clock rate range

2 files changed, 37 insertions, 0 deletions

diff --git a/host/include/uhd/usrp/multi_usrp.hpp b/host/include/uhd/usrp/multi_usrp.hpp
index 2490cc7f8..c70448c3f 100644
--- a/host/include/uhd/usrp/multi_usrp.hpp
+++ b/host/include/uhd/usrp/multi_usrp.hpp
@@ -181,6 +181,26 @@ public:
      */
     virtual double get_master_clock_rate(size_t mboard = 0) = 0;
 
+    /*! Return the range within which the master clock rate can be set for this
+     *  session
+     *
+     * Note that many USRPs do not actually support setting the master clock
+     * rate during a running session. In this case, the range will consist of
+     * a single value, which is the current master clock rate.
+     * Values from this range are valid/sensible inputs to
+     * set_master_clock_rate(), although keep in mind that the latter coerces.
+     *
+     * Examples:
+     * - The B200 series' master clock rate can be changed at runtime and
+     *   will report the true range of supported values
+     * - The X300 series has _two_ discrete options for the clock rate, but will
+     *   always return the clock rate which the USRP was initialized to because
+     *   it cannot be changed at runtime
+     * - The N200 series does not have a configurable clock rate, and will
+     *   always return the same single value as a range
+     */
+    virtual meta_range_t get_master_clock_rate_range(const size_t mboard = 0) = 0;
+
     /*!
      * Get a printable summary for this USRP configuration.
      * \return a printable string
diff --git a/host/lib/usrp/multi_usrp.cpp b/host/lib/usrp/multi_usrp.cpp
index 3af762c82..f9509b7f3 100644
--- a/host/lib/usrp/multi_usrp.cpp
+++ b/host/lib/usrp/multi_usrp.cpp
@@ -465,6 +465,23 @@ public:
         return _tree->access<double>(mb_root(mboard) / "tick_rate").get();
     }
 
+    meta_range_t get_master_clock_rate_range(const size_t mboard)
+    {
+        if (_tree->exists(mb_root(mboard) / "tick_rate/range")) {
+            return _tree->access<meta_range_t>(
+                mb_root(mboard) / "tick_rate/range"
+            ).get();
+        }
+        // The USRP may not have a range defined, in which case we create a
+        // fake range with a single value:
+        const double tick_rate = get_master_clock_rate(mboard);
+        return meta_range_t(
+            tick_rate,
+            tick_rate,
+            0
+        );
+    }
+
     std::string get_pp_string(void){
         std::string buff = str(boost::format(
             "%s USRP:\n"