NVIC: Systick Timer

The HAL_Delay function allows us to insert delays in milliseconds by counting through the interrupt of the Systick timer configured by the HAL library to occur every millisecond ( this is done in the HAL_InitTick function called in HAL_Init ). But we can also use it to establish time periods with a "seed" variable.

#include "bsp.h"

int main(void)
{
    /*seed variable to track the last time we check the systick count*/
    uint32_t tickstart;
    
    /*Init library and the systick timer*/
    HAL_Init();           
    
    /*get the current tick for the first time*/
    tickstart = HAL_GetTick();      

    while (1)
    {
        /* query if already pass 200ms (ticks) since we got the current tick value*/
        if( (HAL_GetTick() - tickstart) >= 200 )
        {
            /*at this point 200ms has been elapsed and we need to take the current tick count again*/
            tickstart = HAL_GetTick();
            /*we do anything we want here every 200ms.             
            but is important the code we wrote here DO NOT spend more than 200ms,
            otherwise periodicity will be affected */        
        }
    }
}

ints.c

/*To track the tick count we need to call the function HAL_IncTick on the vector interrupt*/
void SysTick_Handler( void )
{
    HAL_IncTick( );
}