Timer error

[gocchan]

I accidentally posted it blank.

I'm using TIM4 to develop a prototype product application, and the interval between interrupt events is about 0.4%.

With the minimum required implementation as shown below, the interrupt event occurrence interval was 1.004 ms (The ideal is just 1 ms).

For a 15 minute timer, there will be a large gap of +3.6 seconds.

INTERRUPT_HANDLER(TIM4_UPD_OVF_IRQHandler, 23)
{
	GPIO_WriteReverse(GPIOD, GPIO_PIN_5);
	TIM4_ClearITPendingBit(TIM4_IT_UPDATE);
}
 
void main(void)
{
	CLK_ClockSwitchConfig(CLK_SWITCHMODE_AUTO, CLK_SOURCE_HSE, DISABLE, CLK_CURRENTCLOCKSTATE_ENABLE);
	GPIO_Init(GPIOD, GPIO_PIN_5, GPIO_MODE_OUT_PP_LOW_FAST);
 
	TIM4_DeInit();
	TIM4_TimeBaseInit(TIM4_PRESCALER_64, 250);
	TIM4_ITConfig(TIM4_IT_UPDATE, ENABLE);
	TIM4_Cmd(ENABLE);
 
	enableInterrupts();
 
	while (1)
	{
	}
}

The MCU is STM8S003F3U6TR.

I am using a 16MHz external oscillator with a deviation of ± 30ppm.

What causes this gap? Can software handle it?

Regards,

Gotoda

[AA1 · Accepted solution]

Hi,

ARR value should be one less than the desired value. In your case instead of 250 use 249.

TIM4_TimeBaseInit(TIM4_PRESCALER_64, 249);