/* micro_task_switch_yield.c - measure task context switch time using yield */

/*
 * Copyright (c) 2012-2014 Wind River Systems, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * DESCRIPTION
 * This file contains the benchmark that measure the average time it takes to
 * do context switches between microkernel tasks using task_yield () to force
 * context switch.
 */

#include <zephyr.h>
#include "timestamp.h"  /* reading time */
#include "utils.h"      /* PRINT () and other macros */

/* <stdlib.h> is not supported */
static int abs(int i) { return (i >= 0) ? i : -i; }

/* context switch enough time so our measurement is precise */
#define NB_OF_YIELD     1000

static uint32_t helper_task_iterations;

/**
 *
 * @brief Helper task for measuring task switch latency using yield
 *
 * This task is define in .mdef as SEMYIELDTSK
 *
 * @return N/A
 */
void yieldingTask(void)
{
	while (helper_task_iterations < NB_OF_YIELD) {
		task_yield();
		helper_task_iterations++;
	}
}

/**
 *
 * @brief Entry point for task context switch using yield test
 *
 * @return N/A
 */
void microTaskSwitchYield(void)
{
	uint32_t iterations = 0;
	int32_t  delta;
	uint32_t timestamp;

	PRINT_FORMAT(" 5- Measure average context switch time between tasks"
		     " using (task_yield)");

	bench_test_start();

	/* launch helper task of the same priority than this routine */
	task_start(YIELDTASK);

	/* get initial timestamp */
	timestamp = TIME_STAMP_DELTA_GET(0);

	/* loop until either helper or this routine reaches number of yields */
	while (iterations < NB_OF_YIELD &&
	       helper_task_iterations < NB_OF_YIELD) {
		task_yield();
		iterations++;
	}

	/* get the number of cycles it took to do the test */
	timestamp = TIME_STAMP_DELTA_GET(timestamp);

	/* Ensure both helper and this routine were context switching back &
	 * forth.
	 * For execution to reach the line below, either this routine or helper
	 * routine reached NB_OF_YIELD. The other loop must be at most one
	 * iteration away from reaching NB_OF_YIELD if execute was switching
	 * back and forth.
	 */
	delta = iterations - helper_task_iterations;
	if (bench_test_end() < 0) {
		errorCount++;
		PRINT_OVERFLOW_ERROR();
	} else if (abs(delta) > 1) {
		/* expecting even alternating context switch, seems one routine
		 * called yield without the other having chance to execute
		 */
		errorCount++;
		PRINT_FORMAT(" Error, iteration:%lu, helper iteration:%lu",
			     iterations, helper_task_iterations);
	} else {
		/* task_yield is called (iterations + helper_task_iterations)
		 * times in total.
		 */
		PRINT_FORMAT(" Average task context switch using "
			     "yield %lu tcs = %lu nsec",
			     timestamp / (iterations + helper_task_iterations),
			     SYS_CLOCK_HW_CYCLES_TO_NS_AVG(timestamp,
			     (iterations + helper_task_iterations)));
	}
}