Add drivers_nrf/delay/nrf_delay.h back in

from
https://github.com/ARMmbed/nrf51-sdk/blob/master/source/nordic_sdk/compo
nents/drivers_nrf/delay/nrf_delay.h

cores/nRF5/SDK/components/drivers_nrf/delay/nrf_delay.h

+/*
+ * Copyright (c) Nordic Semiconductor ASA
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ *   1. Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ *   2. Redistributions in binary form must reproduce the above copyright notice, this
+ *   list of conditions and the following disclaimer in the documentation and/or
+ *   other materials provided with the distribution.
+ *
+ *   3. Neither the name of Nordic Semiconductor ASA nor the names of other
+ *   contributors to this software may be used to endorse or promote products
+ *   derived from this software without specific prior written permission.
+ *
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef _NRF_DELAY_H
+#define _NRF_DELAY_H
+
+#include "nrf.h"
+
+/**
+ * @brief Function for delaying execution for number of microseconds.
+ *
+ * @note NRF52 has instruction cache and because of that delay is not precise.
+ *
+ * @param number_of_ms
+ */
+/*lint --e{438, 522} "Variable not used" "Function lacks side-effects" */
+#if defined ( __CC_ARM   )
+
+static __ASM void __INLINE nrf_delay_us(uint32_t volatile number_of_us)
+{
+loop
+        SUBS    R0, R0, #1
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+#ifdef NRF52
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+        NOP
+#endif
+        BNE    loop
+        BX     LR
+}
+
+#elif defined ( __ICCARM__ )
+
+static void __INLINE nrf_delay_us(uint32_t volatile number_of_us)
+{
+__ASM (
+"loop:\n\t"
+       " SUBS R0, R0, #1\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+       " NOP\n\t"
+#ifdef NRF52
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+        " NOP\n\t"
+#endif
+       " BNE.n loop\n\t");
+}
+
+#elif defined ( _WIN32 ) || defined ( __unix ) || defined( __APPLE__ )
+
+__STATIC_INLINE void nrf_delay_us(uint32_t volatile number_of_us);
+
+#ifndef CUSTOM_NRF_DELAY_US
+__STATIC_INLINE void nrf_delay_us(uint32_t volatile number_of_us)
+{}
+#endif
+
+#elif defined ( __GNUC__ )
+
+static void __INLINE nrf_delay_us(uint32_t volatile number_of_us) __attribute__((always_inline));
+static void __INLINE nrf_delay_us(uint32_t volatile number_of_us)
+{
+register uint32_t delay __ASM ("r0") = number_of_us;
+__ASM volatile (
+#ifdef NRF51
+        ".syntax unified\n"
+#endif
+    "1:\n"
+    " SUBS %0, %0, #1\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+#ifdef NRF52
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+    " NOP\n"
+#endif
+    " BNE 1b\n"
+#ifdef NRF51
+    ".syntax divided\n"
+#endif
+    : "+r" (delay));
+}
+#endif
+
+void nrf_delay_ms(uint32_t volatile number_of_ms);
+
+#endif