NuttX cpuload monitoring optimization

- Nuttx only process all suspend & resume scheduling notes when top is running, otherwise only track IDLE
 - convert cpuload and print load to c++
 - delete unused fields from print_load struct
 - update hrt_store_absolute_time (previous unused)

platforms/common/include/px4_platform_common/printload.h

@@ -0,0 +1,79 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2015 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file printload.h
+ *
+ * Print the current system load.
+ *
+ * @author Lorenz Meier <lorenz@px4.io>
+ */
+
+#pragma once
+
+#include <px4_platform_common/px4_config.h>
+
+#include <stdint.h>
+
+#ifndef CONFIG_MAX_TASKS
+#define CONFIG_MAX_TASKS 64
+#endif
+
+struct print_load_s {
+	uint64_t total_user_time{0};
+
+	int running_count{0};
+	int blocked_count{0};
+
+	uint64_t new_time{0};
+	uint64_t interval_start_time{0};
+	uint64_t last_times[CONFIG_MAX_TASKS] {};
+	float interval_time_us{0.f};
+};
+
+__BEGIN_DECLS
+
+__EXPORT void init_print_load(struct print_load_s *s);
+
+__EXPORT void print_load(int fd, struct print_load_s *print_state);
+
+
+typedef void (*print_load_callback_f)(void *user);
+
+/**
+ * Print load to a buffer, and call cb after each written line (buffer will not include '\n')
+ */
+void print_load_buffer(char *buffer, int buffer_length, print_load_callback_f cb, void *user,
+		       struct print_load_s *print_state);
+
+__END_DECLS