tests: xtimer_now64_continuity: initial commit

tests/xtimer_now64_continuity/Makefile

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+export APPLICATION = xtimer_now64_continuity
+include ../Makefile.tests_common
+
+FEATURES_REQUIRED = periph_timer
+
+USEMODULE += xtimer
+
+include $(RIOTBASE)/Makefile.include

tests/xtimer_now64_continuity/README.md

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+Description
+===========
+
+This test measures the difference of two consecutive calls to xtimer_now64() 10k times.
+Should the difference be larger then 1000us, the test fails, otherwise it succeeds.

tests/xtimer_now64_continuity/main.c

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+/*
+ * Copyright (C) 2015 Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       xtimer_now64 continuity test application
+ *
+ * @author      Kaspar Schleiser <kaspar@schleiser.de>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+
+#include "xtimer.h"
+
+#define ITERATIONS (100000LU)
+#define MAXDIFF 1000
+
+int main(void)
+{
+    uint32_t n = ITERATIONS;
+    uint64_t now;
+    uint64_t before = xtimer_now64();
+
+    while(--n) {
+        now = xtimer_now64();
+        if ((now-before) > MAXDIFF) {
+            puts("TEST FAILED.");
+            break;
+        }
+        before = now;
+    }
+
+    if (!n) {
+        puts("TEST SUCCESSFUL.");
+    }
+
+    return 0;
+}