multi_usrp: Amend APIs for GPIO source control

This adds a new API call to multi_usrp: get_gpio_src_banks(). This
returns a list of GPIO banks who's source can be controlled through the
motherboard controller.

The remaining GPIO source methods' docstrings are improved, to explain
the difference between GPIO banks for set_gpio_attr() and
set_gpio_src(). The former controls the actual value on a GPIO bank, and
the latter who drives it. These can be different banks.

1 files changed, 7 insertions, 1 deletions

diff --git a/host/lib/usrp/multi_usrp.cpp b/host/lib/usrp/multi_usrp.cpp
index db21255ae..202f8b2df 100644
--- a/host/lib/usrp/multi_usrp.cpp
+++ b/host/lib/usrp/multi_usrp.cpp
@@ -2249,7 +2249,13 @@ public:
         ));
     }
 
-    // The next three methods are only for RFNoC devices
+    // The next four methods are only for RFNoC devices
+    std::vector<std::string> get_gpio_src_banks(const size_t)
+    {
+        throw uhd::not_implemented_error(
+            "get_gpio_src_banks() not implemented for this motherboard!");
+    }
+
     std::vector<std::string> get_gpio_srcs(const std::string&, const size_t)
     {
         throw uhd::not_implemented_error(