Function to return the number of microseconds since the ESP32 board began running

micros.c

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "esp_system.h"
#include "esp_attr.h"
#include "sdkconfig.h"

portMUX_TYPE microsMux = portMUX_INITIALIZER_UNLOCKED;
unsigned long IRAM_ATTR micros()
{
    static unsigned long lccount = 0;
    static unsigned long overflow = 0;
    unsigned long ccount;
    portENTER_CRITICAL_ISR(&microsMux);
    __asm__ __volatile__ ( "rsr     %0, ccount" : "=a" (ccount) );
    if(ccount < lccount){
        overflow += UINT32_MAX / CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ;
    }
    lccount = ccount;
    portEXIT_CRITICAL_ISR(&microsMux);
    return overflow + (ccount / CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ);
}