Parent last rssi (#1558)

* Added thread api call to get the last rssi for the parent

include/openthread/thread.h

@@ -834,11 +834,23 @@ OTAPI ThreadError OTCALL otThreadGetParentInfo(otInstance *aInstance, otRouterIn
  * The function retrieves the average RSSI for the Thread Parent.
  *
  * @param[in]   aInstance    A pointer to an OpenThread instance.
- * @param[out]  aParentInfo  A pointer to where the parent rssi should be placed.
+ * @param[out]  aParentRssi  A pointer to where the parent rssi should be placed.
  *
  */
 OTAPI ThreadError OTCALL otThreadGetParentAverageRssi(otInstance *aInstance, int8_t *aParentRssi);
 
+/**
+ * The function retrieves the RSSI of the last packet from the Thread Parent.
+ *
+ * @param[in]   aInstance    A pointer to an OpenThread instance.
+ * @param[out]  aLastRssi    A pointer to where the last rssi should be placed.
+ *
+ * @retval kThreadError_None         Successfully retrieved the RSSI data.
+ * @retval kThreadError_Failed       Unable to get RSSI data.
+ * @retval kThreadError_InvalidArgs  @p aLastRssi is NULL.
+ */
+OTAPI ThreadError OTCALL otThreadGetParentLastRssi(otInstance *aInstance, int8_t *aLastRssi);
+
 /**
  * This function pointer is called when Network Diagnostic Get response is received.
  *

src/core/api/thread_api.cpp

@@ -511,6 +511,22 @@ exit:
     return error;
 }
 
+ThreadError otThreadGetParentLastRssi(otInstance *aInstance, int8_t *aLastRssi)
+{
+    ThreadError error = kThreadError_None;
+    Router *parent;
+
+    VerifyOrExit(aLastRssi != NULL, error = kThreadError_InvalidArgs);
+
+    parent = aInstance->mThreadNetif.GetMle().GetParent();
+    *aLastRssi = parent->mLinkInfo.GetLastRss();
+
+    VerifyOrExit(*aLastRssi != LinkQualityInfo::kUnknownRss, error = kThreadError_Failed);
+
+exit:
+    return error;
+}
+
 const char *otGetVersionString(void)
 {
     /**