[router-table] add documentation for {Get/Set}RouterIdRange() (#8532)

src/core/api/thread_ftd_api.cpp

@@ -369,6 +369,9 @@ void otThreadSetThreadVersionCheckEnabled(otInstance *aInstance, bool aEnabled)
 #if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
 void otThreadGetRouterIdRange(otInstance *aInstance, uint8_t *aMinRouterId, uint8_t *aMaxRouterId)
 {
+    AssertPointerIsNotNull(aMinRouterId);
+    AssertPointerIsNotNull(aMaxRouterId);
+
     AsCoreType(aInstance).Get<RouterTable>().GetRouterIdRange(*aMinRouterId, *aMaxRouterId);
 }
 

src/core/thread/router_table.cpp

@@ -122,7 +122,6 @@ Router *RouterTable::Allocate(void)
 
     VerifyOrExit(!mRouters.IsFull());
 
-    // count available router ids
 #if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
     for (uint8_t routerId = mMinRouterId; routerId <= mMaxRouterId; routerId++)
 #else

src/core/thread/router_table.hpp

@@ -314,8 +314,29 @@ public:
     void HandleTimeTick(void);
 
 #if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
+    /**
+     * This method gets the range of Router IDs.
+     *
+     * All the Router IDs in the range `[aMinRouterId, aMaxRouterId]` are allowed. This is intended for testing only.
+     *
+     * @param[out]  aMinRouterId   Reference to return the minimum Router ID.
+     * @param[out]  aMaxRouterId   Reference to return the maximum Router ID.
+     *
+     */
     void GetRouterIdRange(uint8_t &aMinRouterId, uint8_t &aMaxRouterId) const;
 
+    /**
+     * This method sets the range of Router IDs.
+     *
+     * All the Router IDs in the range `[aMinRouterId, aMaxRouterId]` are allowed. This is intended for testing only.
+     *
+     * @param[in]  aMinRouterId   The minimum Router ID.
+     * @param[in]  aMaxRouterId   The maximum Router ID.
+     *
+     * @retval kErrorNone          Successfully set the Router ID range.
+     * @retval kErrorInvalidArgs   The given range is not valid.
+     *
+     */
     Error SetRouterIdRange(uint8_t aMinRouterId, uint8_t aMaxRouterId);
 #endif