diff --git a/targets/TARGET_NUVOTON/nu_timer.c b/targets/TARGET_NUVOTON/nu_timer.c
new file mode 100644
index 0000000000..ca3c2a10a2
--- /dev/null
+++ b/targets/TARGET_NUVOTON/nu_timer.c
@@ -0,0 +1,47 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2015-2016 Nuvoton
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "nu_timer.h"
+#include "mbed_power_mgmt.h"
+#include "mbed_critical.h"
+
+void nu_countdown_init(struct nu_countdown_ctx_s *ctx, us_timestamp_t interval_us)
+{
+    core_util_critical_section_enter();
+    sleep_manager_lock_deep_sleep();
+    ctx->_ticker_data = get_us_ticker_data();
+    ctx->_interval_end_us = ticker_read_us(ctx->_ticker_data) + interval_us;
+    ctx->_expired = false;
+    core_util_critical_section_exit();
+}
+
+bool nu_countdown_expired(struct nu_countdown_ctx_s *ctx)
+{
+    core_util_critical_section_enter();
+    if (! ctx->_expired) {
+        ctx->_expired = ticker_read_us(ctx->_ticker_data) >= ctx->_interval_end_us;
+    }
+    core_util_critical_section_exit();
+    
+    return ctx->_expired;
+}
+
+void nu_countdown_free(struct nu_countdown_ctx_s *ctx)
+{
+    core_util_critical_section_enter();
+    sleep_manager_unlock_deep_sleep();
+    core_util_critical_section_exit();
+}
diff --git a/targets/TARGET_NUVOTON/nu_timer.h b/targets/TARGET_NUVOTON/nu_timer.h
index 7342fe92b5..00f233b4e6 100644
--- a/targets/TARGET_NUVOTON/nu_timer.h
+++ b/targets/TARGET_NUVOTON/nu_timer.h
@@ -20,8 +20,6 @@
 #include <stdint.h>
 #include <stdbool.h>
 #include "cmsis.h"
-#include "mbed_power_mgmt.h"
-#include "mbed_critical.h"
 #include "ticker_api.h"
 #include "us_ticker_api.h"
 
@@ -58,33 +56,9 @@ struct nu_countdown_ctx_s {
     bool                    _expired;           // Expired or not
 };
 
-__STATIC_INLINE void nu_countdown_init(struct nu_countdown_ctx_s *ctx, us_timestamp_t interval_us)
-{
-    core_util_critical_section_enter();
-    sleep_manager_lock_deep_sleep();
-    ctx->_ticker_data = get_us_ticker_data();
-    ctx->_interval_end_us = ticker_read_us(ctx->_ticker_data) + interval_us;
-    ctx->_expired = false;
-    core_util_critical_section_exit();
-}
-
-__STATIC_INLINE bool nu_countdown_expired(struct nu_countdown_ctx_s *ctx)
-{
-    core_util_critical_section_enter();
-    if (! ctx->_expired) {
-        ctx->_expired = ticker_read_us(ctx->_ticker_data) >= ctx->_interval_end_us;
-    }
-    core_util_critical_section_exit();
-    
-    return ctx->_expired;
-}
-
-__STATIC_INLINE void nu_countdown_free(struct nu_countdown_ctx_s *ctx)
-{
-    core_util_critical_section_enter();
-    sleep_manager_unlock_deep_sleep();
-    core_util_critical_section_exit();
-}
+void nu_countdown_init(struct nu_countdown_ctx_s *ctx, us_timestamp_t interval_us);
+bool nu_countdown_expired(struct nu_countdown_ctx_s *ctx);
+void nu_countdown_free(struct nu_countdown_ctx_s *ctx);
 
 #ifdef __cplusplus
 }