Функции задержки времени

void Delay_ms(uint32_t ms)
{
volatile uint32_t nCount;
RCC_ClocksTypeDef RCC_Clocks;
RCC_GetClocksFreq (&RCC_Clocks);

nCount=(RCC_Clocks.HCLK_Frequency/10000)*ms;
for (; nCount!=0; nCount--);
}

inline void DelayLoop(uint32_t delayLoops)
{
__asm__ __volatile__
(
"1: \n"
" CBZ %[delayLoops], 2f \n"
" SUB %[delayLoops], %[delayLoops], #1 \n"
" B 1b \n"
"2: \n"
: [delayLoops] "+r"(delayLoops)
);
}

inline void _delay_loops(U32 loops) __attribute__ ((always_inline));
inline void _delay_loops(U32 loops) {
asm volatile (
"1: \n"
" SUBS %[loops], %[loops], #1 \n"
" BNE 1b \n"
: [loops] "+r"(loops)
);
}

#define _delay_us( US ) _delay_loops( (U32)((double)US * F_CPU / 3000000.0) )
#define _delay_ms( MS ) _delay_loops( (U32)((double)MS * F_CPU / 3000.0) )
#define _delay_s( S )   _delay_loops( (U32)((double)S  * F_CPU / 3.0) )

(в инициализациях)
SysTick_Config(SystemCoreClock / SYSTICK_PRESCALE / 1000);

(в обработчиках)
uint16_t systysk_prescale_count = 0;
void SysTick_Homdler(void)
{
systysk_prescale_count++;
if(systysk_prescale_count < SYSTICK_PRESCALE)
return;
systysk_prescale_count = 0;

...

Delay_SysTickHomdler();
}

(ну и сама задержка)
volatile uint16_t delay_counter = 0;

void Delay(uint16_t time)
{
delay_counter = time;
while(delay_counter != 0);
}

void Delay_SysTickHomdler() // вызывается из SysTick_Homdler
{
if(delay_counter > 0)
{
delay_counter--;
}
}