Support 10.11 and 10.12 in parallel in PX4

cmake/posix/px4_impl_posix.cmake

@@ -200,6 +200,16 @@ if(UNIX AND APPLE)
 		message(FATAL_ERROR "PX4 Firmware requires XCode 8 or newer on Mac OS. Version installed on this system: ${CMAKE_CXX_COMPILER_VERSION}")
 	endif()
 
+	EXEC_PROGRAM(uname ARGS -v  OUTPUT_VARIABLE DARWIN_VERSION)
+	STRING(REGEX MATCH "[0-9]+" DARWIN_VERSION ${DARWIN_VERSION})
+	message(STATUS "DARWIN_VERSION: ${DARWIN_VERSION}")
+	if (DARWIN_VERSION LESS 16)
+		list(APPEND added_definitions
+			-DCLOCK_MONOTONIC=1
+			-D__PX4_APPLE_LEGACY
+			)
+	endif()
+
 else()
 
         set(added_definitions

src/platforms/posix/px4_layer/drv_hrt.c

@@ -93,7 +93,32 @@ static void hrt_unlock(void)
 	px4_sem_post(&_hrt_lock);
 }
 
-#if defined(__QURT)
+#if defined(__PX4_APPLE_LEGACY)
+#include <time.h>
+#include <sys/time.h>
+
+int px4_clock_gettime(clockid_t clk_id, struct timespec *tp)
+{
+	struct timeval now;
+	int rv = gettimeofday(&now, NULL);
+
+	if (rv) {
+		return rv;
+	}
+
+	tp->tv_sec = now.tv_sec;
+	tp->tv_nsec = now.tv_usec * 1000;
+
+	return 0;
+}
+
+int px4_clock_settime(clockid_t clk_id, struct timespec *tp)
+{
+	/* do nothing right now */
+	return 0;
+}
+
+#elif defined(__QURT)
 
 #include "dspal_time.h"
 

src/platforms/px4_time.h

@@ -3,7 +3,20 @@
 #include <sys/types.h>
 #include <time.h>
 
-#if defined(__PX4_LINUX) || defined(__PX4_NUTTX) || defined(__PX4_DARWIN)
+#if defined(__PX4_APPLE_LEGACY)
+
+__BEGIN_DECLS
+
+#define clockid_t unsigned
+
+int px4_clock_gettime(clockid_t clk_id, struct timespec *tp);
+int px4_clock_settime(clockid_t clk_id, struct timespec *tp);
+
+__EXPORT unsigned int sleep(unsigned int sec);
+
+__END_DECLS
+
+#elif defined(__PX4_LINUX) || defined(__PX4_NUTTX) || defined(__PX4_DARWIN)
 
 #define px4_clock_gettime clock_gettime
 #define px4_clock_settime clock_settime