Import Mbed OS hard-float snapshot

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/us_ticker.h

@@ -0,0 +1,27 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2018 ARM Limited and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * 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.
+ */
+
+#ifndef US_TICKER_H
+#define US_TICKER_H
+
+/* TIMER0 is reserved for SoftDevice. We will use TIMER1 for us ticker
+ * which counter size is 32 bits. */
+
+#define US_TICKER_COUNTER_BITS        32u
+#define US_TICKER_FREQ                1000000
+
+#endif // US_TICKER_H