HAL_Linux: add methods for native clock info methods

libraries/AP_HAL_Linux/system.cpp

@@ -79,4 +79,43 @@ uint64_t millis64()
                    (state.start_time.tv_nsec*1.0e-9)));
 }
 
+
+uint32_t native_micros()
+{
+    return native_micros64() & 0xFFFFFFFF;
+}
+
+uint32_t native_millis()
+{
+    return native_millis64() & 0xFFFFFFFF;
+}
+
+/*
+  we define a millis16() here to avoid an issue with sitl builds in cygwin
+ */
+uint16_t native_millis16()
+{
+    return native_millis64() & 0xFFFF;
+}
+    
+
+uint64_t native_micros64()
+{
+    struct timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    return 1.0e6*((ts.tv_sec + (ts.tv_nsec*1.0e-9)) -
+                  (state.start_time.tv_sec +
+                   (state.start_time.tv_nsec*1.0e-9)));
+}
+
+uint64_t native_millis64()
+{
+    struct timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    return 1.0e3*((ts.tv_sec + (ts.tv_nsec*1.0e-9)) -
+                  (state.start_time.tv_sec +
+                   (state.start_time.tv_nsec*1.0e-9)));
+}
+
+
 } // namespace AP_HAL