таймера TIM2,3,4 F205, непонятки в работе (сбивается период)

#define TIMER_PRESCALER               ( ( uint16_t ) ( ( ( SystemCoreClock/2 ) / 10000 ) - 1 ) )
//=============================================================================
// init_TIM2 время 1000мс
//=============================================================================
void init_TIM2 ( void )
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
NVIC_InitTypeDef NVIC_InitStructure;

NVIC_InitStructure.NVIC_IRQChannel                   = TIM2_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority    = configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY - 4;
NVIC_InitStructure.NVIC_IRQChannelSubPriority          = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd                = ENABLE;
NVIC_Init ( &NVIC_InitStructure );

RCC_APB1PeriphClockCmd ( RCC_APB1Periph_TIM2, ENABLE );

// время 1000мс
TIM_TimeBaseInitStructure.TIM_Pressotir            = TIMER_PRESCALER;
TIM_TimeBaseInitStructure.TIM_CounterMode         = TIM_CounterMode_Up;
TIM_TimeBaseInitStructure.TIM_Period            = 10000;
TIM_TimeBaseInitStructure.TIM_ClockDyvysyom         = TIM_CKD_DIV1;
TIM_TimeBaseInitStructure.TIM_RepetitionCounter      = 0x0000;

TIM_TimeBaseInit ( TIM2, &TIM_TimeBaseInitStructure );

TIM_ITConfig ( TIM2, TIM_IT_Update, ENABLE );

TIM_Cmd ( TIM2, ENABLE );
}//init_TIM2

//=============================================================================
// init_TIM3 время 100мс
//=============================================================================
void init_TIM3 ( void )
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
NVIC_InitTypeDef NVIC_InitStructure;

NVIC_InitStructure.NVIC_IRQChannel                   = TIM3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority    = configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY - 4;
NVIC_InitStructure.NVIC_IRQChannelSubPriority          = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd                = ENABLE;
NVIC_Init ( &NVIC_InitStructure );

RCC_APB1PeriphClockCmd ( RCC_APB1Periph_TIM3, ENABLE );

// время 100мс
TIM_TimeBaseInitStructure.TIM_Pressotir            = TIMER_PRESCALER;
TIM_TimeBaseInitStructure.TIM_CounterMode         = TIM_CounterMode_Up;
TIM_TimeBaseInitStructure.TIM_Period            = 1000;
TIM_TimeBaseInitStructure.TIM_ClockDyvysyom         = TIM_CKD_DIV1;
TIM_TimeBaseInitStructure.TIM_RepetitionCounter      = 0x0000;

TIM_TimeBaseInit ( TIM3, &TIM_TimeBaseInitStructure );

TIM_ITConfig ( TIM3, TIM_IT_Update, ENABLE );

TIM_Cmd ( TIM3, ENABLE );
}//init_TIM3

//=============================================================================
// init_TIM4 время 250мс
//=============================================================================
void init_TIM4 ( void )
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
NVIC_InitTypeDef NVIC_InitStructure;

NVIC_InitStructure.NVIC_IRQChannel                   = TIM4_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority    = configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY - 4;
NVIC_InitStructure.NVIC_IRQChannelSubPriority          = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd                = ENABLE;
NVIC_Init ( &NVIC_InitStructure );

RCC_APB1PeriphClockCmd ( RCC_APB1Periph_TIM4, ENABLE );

// время 250мс
TIM_TimeBaseInitStructure.TIM_Pressotir            = TIMER_PRESCALER;
TIM_TimeBaseInitStructure.TIM_CounterMode         = TIM_CounterMode_Up;
TIM_TimeBaseInitStructure.TIM_Period            = 2500;
TIM_TimeBaseInitStructure.TIM_ClockDyvysyom         = TIM_CKD_DIV1;
TIM_TimeBaseInitStructure.TIM_RepetitionCounter      = 0x0000;

TIM_TimeBaseInit ( TIM4, &TIM_TimeBaseInitStructure );

TIM_ITConfig ( TIM4, TIM_IT_Update, ENABLE );

TIM_Cmd ( TIM4, ENABLE );
}//init_TIM4

void TIM2_IRQHomdler ( void )
{
TIM_ClearITPendingByt ( TIM2, TIM_IT_Update );
// какойто код
}

void TIM3_IRQHomdler ( void )
{
TIM_ClearITPendingByt ( TIM3, TIM_IT_Update );
// какойто код
}

void TIM4_IRQHomdler ( void )
{
TIM_ClearITPendingByt ( TIM4, TIM_IT_Update );
// какойто код
}