Added CPU UID target implementation for EFM32 devices

Author: MikeDK

targets/TARGET_Silicon_Labs/TARGET_EFM32/cpu_uid_api.c

@@ -0,0 +1,50 @@
+/***************************************************************************//**
+ * @file cpu_uid_api.c
+ *******************************************************************************
+ * @section License
+ * <b>(C) Copyright 2017 Silicon Labs, http://www.silabs.com</b>
+ *******************************************************************************
+ *
+ * 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.
+ *
+ ******************************************************************************/
+
+#include "device.h"
+
+#if DEVICE_CPUUID
+
+#include "em_system.h"
+#include "cpu_uid_api.h"
+
+#define UID_LENGTH      8
+
+int cpu_uid_get_length(void)
+{
+    return UID_LENGTH;
+}
+
+void cpu_uid_get_uid(uint8_t *uid)
+{
+    int pos = 0;
+    uint64_t tempuid = SYSTEM_GetUnique();
+
+    for (int i = (UID_LENGTH-1); i >= 0; --i)
+    {
+        uid[pos] = (uint8_t)((tempuid >> (i*8)) & 0xFF);
+        ++pos;
+    }
+}
+
+#endif