i.MX 7 Cortex-M4 FreeRTOS C micro benchmark

main.c

#include <math.h>
#include "FreeRTOS.h"
#include "task.h"
#include "board.h"
#include "debug_console_imx.h"

double squareroot(double x)
{
    double it = x;
    while (fabs(it*it - x) > 1e-13) {
        it = it - (it*it-x)/(2*it);
    }
    return it;
}

void benchmark(void)
{
    const int num_iter = 1000;
    TickType_t t = xTaskGetTickCount();
    volatile double sum_real = 0;
    for (int i = 0; i < num_iter; i++) {
        sum_real += squareroot(10000.0);
    }
    TickType_t ttot = xTaskGetTickCount() - t;
    PRINTF("%d milliseconds\n\r", ttot);
}

void BenchmarkTask(void *pvParameters)
{
    PRINTF("\r\nBenchmark!\n\n\r");

    while(1)
    {
	    benchmark();
    }
}

int main(void)
{
    // Initialize demo application pins setting and clock setting.
    hardware_init();

    // Create a demo task which will print Hello world and echo user's input.
    xTaskCreate(BenchmarkTask, "Benchmark Task", configMINIMAL_STACK_SIZE,
                NULL, tskIDLE_PRIORITY+1, NULL);

    // Start FreeRTOS scheduler.
    vTaskStartScheduler();

    // Should never reach this point.
    while (true);
}