diff --git a/repos/os/include/rtc_session/client.h b/repos/os/include/rtc_session/client.h
index 8a84ee812..8aaadf031 100644
--- a/repos/os/include/rtc_session/client.h
+++ b/repos/os/include/rtc_session/client.h
@@ -23,9 +23,18 @@ namespace Rtc { struct Session_client; }
 
 struct Rtc::Session_client : Genode::Rpc_client<Session>
 {
+	/**
+	 * Constructor
+	 *
+	 * \param session  session capability
+	 */
 	Session_client(Genode::Capability<Session> cap)
 	: Genode::Rpc_client<Session>(cap) {}
 
+	/***********************
+	 ** Session interface **
+	 ***********************/
+
 	Timestamp current_time() override { return call<Rpc_current_time>(); }
 };
 
diff --git a/repos/os/include/rtc_session/rtc_session.h b/repos/os/include/rtc_session/rtc_session.h
index cc05311f5..cc5000922 100644
--- a/repos/os/include/rtc_session/rtc_session.h
+++ b/repos/os/include/rtc_session/rtc_session.h
@@ -7,7 +7,7 @@
 
 /*
  * Copyright (C) 2012 Intel Corporation
- * Copyright (C) 2013-2017 Genode Labs GmbH
+ * Copyright (C) 2013-2019 Genode Labs GmbH
  *
  * This file is part of the Genode OS framework, which is distributed
  * under the terms of the GNU Affero General Public License version 3.
@@ -26,6 +26,9 @@ namespace Rtc {
 }
 
 
+/*
+ * RTC value
+ */
 struct Rtc::Timestamp
 {
 	unsigned microsecond;
@@ -53,8 +56,21 @@ struct Rtc::Session : Genode::Session
 
 	enum { CAP_QUOTA = 2 };
 
+	/***********************
+	 ** Session interface **
+	 ***********************/
+
+	/**
+	 * Query current time
+	 *
+	 * \return  RTC value as structed timestamp
+	 */
 	virtual Timestamp current_time() = 0;
 
+	/*******************
+	 ** RPC interface **
+	 *******************/
+
 	GENODE_RPC(Rpc_current_time, Timestamp, current_time);
 	GENODE_RPC_INTERFACE(Rpc_current_time);
 };