Best way of implementing stopwatch

[paramasivan]

Posted on March 31, 2015 at 08:20

Hi,

Which one is the best way of implementing stopwatch in stm32f429? Currently i am using soft timers for stopwatch. But it has time  drift in long period when compared into my mobile stopwatch. I have using RTC also. Is there any method using with RTC module for stopwatch. Thanks in advance. #timer #stm32 #interrupt #!stm32f4-disco #exti

[Tesla DeLorean]

Posted on March 31, 2015 at 15:03

Neither the LSI or HSI are particularly accurate, use crystals?

[paramasivan]

Posted on April 02, 2015 at 09:50

Hi Clive,

i am using external crystal 8MHz and my system core clock is 180MHZ. Even I have tried timer 2 for stopwatch. But still my stopwatch is little bit faster than mobile stopwatch. TIM_TimeBaseStructure.TIM_Prescaler = 1799; //timer input  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  TIM_TimeBaseStructure.TIM_Period = 1000;  TIM_TimeBaseStructure.TIM_ClockDivision = 0;  TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);    NVIC_SetPriority(TIM2_IRQn,0);    TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE); TIM_ARRPreloadConfig(TIM2, ENABLE);void TIM2_IRQHandler(void){   TIM2->SR &=0xFFFE;    SW_Update = 1; SW_MSecs ++;   if(SW_MSecs == 100)   {     SW_MSecs =0;          if(GPIO_ReadOutputDataBit(GPIOB,GPIO_Pin_12))      // for test, its exactly switch                                                                                                          1secs         GPIOB->BSRRH = GPIO_Pin_12;       else           GPIOB->BSRRL = GPIO_Pin_12;          SW_Secs ++;     if(SW_Secs == 60)     {       SW_Secs =0;       SW_Mins ++;       if(SW_Mins == 60)       {         SW_Mins =0;       }     }   } //}}

[paramasivan]

Posted on April 02, 2015 at 13:07I have also tried in the following manner TIM_TimeBaseStructure.TIM_Prescaler = 1799; //timer input  TIM_TimeBaseStructure.TIM_Period = 1000 -1;timer has generate interrupt at every 9.900 ms only. I couldn't understand why the timer did't get 10 ms interrupt.

[AvaTar]

Posted on April 02, 2015 at 13:23

10 ms isn't really very demanding.

I usually handle such tasks with the SysTick timer:

RCC_ClocksTypeDef RCC_Clocks;
/* SysTick event each 10ms */
RCC_GetClocksFreq (&RCC_Clocks);
SysTick_Config (RCC_Clocks.HCLK_Frequency / 100);

[Tesla DeLorean]

Posted on April 02, 2015 at 15:23

Round here we'd use an oscilloscope.

Would confirm the input HSE clock, and PLL/CPU clock, via the MCO (PA8) pin.

[paramasivan]

Posted on April 07, 2015 at 14:11I am getting 181.4 MHZ output on MCO2 pin.I am using 32.768 Mhz crystal for RTC. Shall i create timer interupt using the LSE clock input? or any other way to calibrate the HSE with LSE crystal clock?What about the sub seconds in RTC? Is it create any interrupt to update my sub seconds in my stopwatch?