Add conversions and mixer tests. Work in progress

Tools/tests-host/hrt.cpp

@@ -0,0 +1,13 @@
+#include <sys/time.h>
+#include <inttypes.h>
+#include <drivers/drv_hrt.h>
+#include <stdio.h>
+
+uint64_t hrt_absolute_time()
+{
+    struct timeval te; 
+    gettimeofday(&te, NULL); // get current time
+    unsigned long long us = static_cast<uint64_t>(te.tv_sec) * 1e6 + te.tv_usec; // caculate us
+    printf("us: %lld\n", us);
+    return us;
+}