os/time: Add windows impl of os_realtime_get_ns

src/xrt/auxiliary/os/CMakeLists.txt

@@ -9,7 +9,14 @@
 # by applications like the OpenXR runtime library.
 #
 
-add_library(aux_os STATIC os_documentation.h os_hid.h os_hid_hidraw.c os_threading.h)
+add_library(
+	aux_os STATIC
+	os_documentation.h
+	os_hid.h
+	os_hid_hidraw.c
+	os_threading.h
+	os_time.cpp
+	)
 target_link_libraries(aux_os PUBLIC aux-includes xrt-pthreads)
 
 # Only uses normal Windows libraries, doesn't add anything extra.

src/xrt/auxiliary/os/os_time.cpp

@@ -0,0 +1,31 @@
+// Copyright 2023, Collabora, Ltd.
+// SPDX-License-Identifier: BSL-1.0
+/*!
+ * @file
+ * @brief  Wrapper around OS native time functions.
+ *
+ * These should be preferred over directly using native OS time functions in
+ * potentially-portable code. Additionally, in most cases these are preferred
+ * over timepoints from @ref time_state for general usage in drivers, etc.
+ *
+ * @author Christoph Haag <christoph.haag@collabora.com>
+ *
+ * @ingroup aux_os
+ */
+
+#include "xrt/xrt_config_os.h"
+
+#ifdef XRT_OS_WINDOWS
+
+#include <inttypes.h>
+#include <chrono>
+
+extern "C" uint64_t
+os_realtime_get_ns(void)
+{
+	auto now = std::chrono::system_clock::now();
+	auto nsecs = std::chrono::time_point_cast<std::chrono::nanoseconds>(now);
+	auto ret = nsecs.time_since_epoch().count();
+	return ret;
+}
+#endif

src/xrt/auxiliary/os/os_time.h

@@ -165,6 +165,16 @@ static inline uint64_t
 os_realtime_get_ns(void);
 #endif
 
+#if defined(XRT_OS_WINDOWS)
+/*!
+ * Return a realtime clock in nanoseconds
+ *
+ * @ingroup aux_os_time_extra
+ */
+uint64_t
+os_realtime_get_ns(void);
+#endif
+
 #if defined(XRT_OS_WINDOWS) || defined(XRT_DOXYGEN)
 /*!
  * @brief Return a qpc freq in nanoseconds.