1Hz interrupt from TIM3 ?

[antonius]

Dear Members,

How can I get exactly 1Hz interrupt from TIM3 ?

I use STM32F4 Discovery and looking at TIM_TimeBase Example, but I can not get exactly 1Hz yet...

Thanks

Code :

TIM_OCInitTypeDef  TIM_OCInitStructure;
__IO uint16_t CCR1_Val = 54618;
__IO uint16_t CCR2_Val = 27309;
__IO uint16_t CCR3_Val = 13654;
__IO uint16_t CCR4_Val = 6826;
 
 
/* -----------------------------------------------------------------------
    TIM3 Configuration: Output Compare Timing Mode:
    
    In this example TIM3 input clock (TIM3CLK) is set to 2 * APB1 clock (PCLK1), 
    since APB1 prescaler is different from 1.   
      TIM3CLK = 2 * PCLK1  
      PCLK1 = HCLK / 4 
      => TIM3CLK = HCLK / 2 = SystemCoreClock /2
          
    To get TIM3 counter clock at 50 MHz, the prescaler is computed as follows:
       Prescaler = (TIM3CLK / TIM3 counter clock) - 1
       Prescaler = ((SystemCoreClock /2) /50 MHz) - 1
                                              
    CC1 update rate = TIM3 counter clock / CCR1_Val = 9.154 Hz
    ==> Toggling frequency = 4.57 Hz
    
    C2 update rate = TIM3 counter clock / CCR2_Val = 18.31 Hz
    ==> Toggling frequency = 9.15 Hz
    
    CC3 update rate = TIM3 counter clock / CCR3_Val = 36.62 Hz
    ==> Toggling frequency = 18.31 Hz
    
    CC4 update rate = TIM3 counter clock / CCR4_Val = 73.25 Hz
    ==> Toggling frequency = 36.62 Hz
 
/* Compute the prescaler value */
  //PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 500000) - 1;
	PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 6826) - 1;  //TIM3 counter clock at 6826Hz
 
  /* Time base configuration */
  TIM_TimeBaseStructure.TIM_Period = 65535;
  TIM_TimeBaseStructure.TIM_Prescaler = 0;
  TIM_TimeBaseStructure.TIM_ClockDivision = 0;
  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
 
  TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
 
  /* Prescaler configuration */
  TIM_PrescalerConfig(TIM3, PrescalerValue, TIM_PSCReloadMode_Immediate);
 
  /* Output Compare Timing Mode configuration: Channel1 */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_Timing;
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = CCR1_Val;
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
 
  TIM_OC1Init(TIM3, &TIM_OCInitStructure);
 
  TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Disable);
 
  /* Output Compare Timing Mode configuration: Channel2 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = CCR2_Val;
 
  TIM_OC2Init(TIM3, &TIM_OCInitStructure);
 
  TIM_OC2PreloadConfig(TIM3, TIM_OCPreload_Disable);
 
  /* Output Compare Timing Mode configuration: Channel3 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = CCR3_Val;
 
  TIM_OC3Init(TIM3, &TIM_OCInitStructure);
 
  TIM_OC3PreloadConfig(TIM3, TIM_OCPreload_Disable);
 
  /* Output Compare Timing Mode configuration: Channel4 */
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
  TIM_OCInitStructure.TIM_Pulse = CCR4_Val;
 
  TIM_OC4Init(TIM3, &TIM_OCInitStructure);
 
  TIM_OC4PreloadConfig(TIM3, TIM_OCPreload_Disable);
   
  /* TIM Interrupts enable */
  TIM_ITConfig(TIM3, TIM_IT_CC1 | TIM_IT_CC2 | TIM_IT_CC3 | TIM_IT_CC4, ENABLE);

This example shows how to configure the TIM peripheral in Output Compare Timing 
mode with the corresponding Interrupt requests for each channel in order to generate
4 different time bases.
 
The TIM3CLK frequency is set to SystemCoreClock / 2 (Hz), to get TIM3 counter 
clock at 500 KHz so the Prescaler is computed as following:
   - Prescaler = (TIM3CLK / TIM3 counter clock) - 1
 
SystemCoreClock is set to 168 MHz for STM32F4xx Devices Revision A.
 
The TIM3 CC1 register value is equal to 54618, 
CC1 update rate = TIM3 counter clock / CCR1_Val = 9.154 Hz,
so the TIM3 Channel 1 generates an interrupt each 109.2ms
 
The TIM3 CC2 register is equal to 27309, 
CC2 update rate = TIM3 counter clock / CCR2_Val = 18.31 Hz
so the TIM3 Channel 2 generates an interrupt each 54.6ms
 
The TIM3 CC3 register is equal to 13654, 
CC3 update rate = TIM3 counter clock / CCR3_Val = 36.62 Hz
so the TIM3 Channel 3 generates an interrupt each 27.3ms
 
The TIM3 CC4 register is equal to 6826, 
CC4 update rate = TIM3 counter clock / CCR4_Val =  73.25 Hz
so the TIM3 Channel 4 generates an interrupt each 13.65ms.
 
When the counter value reaches the Output compare registers values, the Output 
Compare interrupts are generated and, in the handler routine, 4 pins(PD.12, PD.13,
PD.14 and PD.15) are toggled with the following frequencies: 
 
- PD.12:  4.57 Hz (CC1)
- PD.13:  9.15 Hz (CC2)
- PD.14: 18.31 Hz (CC3) 
- PD.15: 36.62 Hz (CC4)

[antonius]

The file : STM32F4-Discovery_FW_V1.1.0\Project\Peripheral_Examples\TIM_TimeBase\readme.txt

[prain]

Getting 1Hz is not possible with this prescaler value. Increase prescaler value. for example set timer clock to 1KHz:

PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 1000) - 1;

then set your desired CCx channel to 1000 :

__IO uint16_t CCR1_Val = 1000;

[TDK]

The CCR values for TIM1 are 16-bit (max of 65535), so you need to increase the prescaler if you want a 1Hz interrupt.

Use

PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 50000) - 1;

to set the timer clock to 50kHz and use TIM_Period = 49999 to have an update interrupt at 1 Hz.

That example is showing how to toggle LEDs multiple times within an update period. Doesn't seem like what you're asking for.

[TDK]

> PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 1000) - 1;

At a clock of 168 MHz, this will overflow 16 bits.

[S.Ma]

The precision also depends on clock tolerances, so don t use HSI internal oscillators. Ideally use 32.768khz LSE clock as RTC purpose is calendar and time clock. In some products like STM32L4 48MHz can be generated by MSI from LSE.

[antonius]

How​ to avoid overflow ? I want to get 1Hz, 0.5Hz, 0.1Hz and 0.05Hz Thanks

[TDK]

Read my answer below.

[antonius]

I don't understand, if I want to get 0.5 Hz ?

What's the value for

__IO uint16_t CCR1_Val = 49999; // 1Hz

__IO uint16_t CCR2_Val = 49999*2; // to get 0.5Hz ==> correct me ?

if

TIM_Period = 49999

and

TIM3 counter clock at 50 KHz, I'm thinking to reduce TIM3 counter clock to 1KHz, but I can't get a good result ?

Cheers,

[TDK]

> 49999*2

This overflows. What did you have to do before to prevent it from overflowing?