STM32F0 TIM17 prescale settings has no effect on update interrupt

[Kurt Alber]

Posted on February 21, 2018 at 10:02

I generated my code from STM32CubeMx and wanted to generate a update event every 1µs. I work with the internal clock at 48MHz, which should be with Prescaler:0 and Autoreload:47 result to 1µs.

I use a STM32F030 with TrueStudio V.9.0.0

**generated code**

/* TIM17 init function */

    static void MX_TIM17_Init(void)

    {

      LL_TIM_InitTypeDef TIM_InitStruct;

      /* Peripheral clock enable */

      LL_APB1_GRP2_EnableClock(LL_APB1_GRP2_PERIPH_TIM17);

      /* TIM17 interrupt Init */

      NVIC_SetPriority(TIM17_IRQn, 3);

      NVIC_EnableIRQ(TIM17_IRQn);

      TIM_InitStruct.Prescaler = 0;

      TIM_InitStruct.CounterMode = LL_TIM_COUNTERMODE_UP;

      TIM_InitStruct.Autoreload = 47;

      TIM_InitStruct.ClockDivision = LL_TIM_CLOCKDIVISION_DIV1;

      TIM_InitStruct.RepetitionCounter = 0;

      LL_TIM_Init(TIM17, &TIM_InitStruct);

      LL_TIM_EnableARRPreload(TIM17);

    }

I added in my init:

 

LL_TIM_EnableIT_UPDATE(TIM17);

    LL_TIM_EnableCounter(TIM17);

In the IRQ_Handler i toggle a PIN:

void TIM17_IRQHandler(void)

    {

      /* USER CODE BEGIN TIM17_IRQn 0 */

        LL_GPIO_TogglePin(LED_D2_2_GPIO_Port,LED_D2_2_Pin);

      /* USER CODE END TIM17_IRQn 0 */

      /* USER CODE BEGIN TIM17_IRQn 1 */

      /* USER CODE END TIM17_IRQn 1 */

    }

After flashing my device with the code it generates a Signal with Frequency 889kHz with Pulsewidth of 564ns measured with Oscilloscope. Changes on Prescaler or Autoreload does not affect this output, it stays right away at T_Pulse=564ns or F=889kHz.

Any idea what I am missing here?

Register output from debugging:

    CR1:0x81              CR2:0

    DIER:0x01             SR:0x03

    CCMR1_O/I:0        CCER:0

    PSC:0                    ARR:0x2f

    RCR:0                   CCR1:0

    BDTR:0                 DCR:0    

    DMAR:0x81

[Tesla DeLorean]

Posted on February 21, 2018 at 13:02

Well 0x2F == 47, so you'd likely want to look at why you aren't changing PSC or ARR with whatever interaction you are having with them.

[Kurt Alber]

Posted on February 21, 2018 at 13:23

Sorry I do not  understand your suggestion. I have no further interactions with ARR and PSC except the posted code.

Hopefully this explains it further:

I have two issues:

1st:

  ARR=0x2f with PSC=0 with 48MHz Clock should give me 1µs ticks, but it doesn't, instead I get 564ns ticks.

2nd:

 When I enter different settings to ARR and PSC it does not change a bit, it remains at 564ns ticks.

[Tesla DeLorean]

Posted on February 21, 2018 at 14:07

Ok, yes at 48 MHz I'd expect a clean 1 MHz 

Problem likely that you can't interrupt at that rate,you'd want the TIM in PWM or TOGGLE mode to output a signal directly on a TIMx_CHx pin.

You're observing the processor saturate with the task given it.

[Kurt Alber]

Posted on February 21, 2018 at 16:43

Thank you!

I have a configured PWM Timer on TIM3 which is successful working with 4MHz output. Therefore I assume the system clock is at 48MHz because it works as designed;

But, If I enable UIE on TIM17:

LL_TIM_EnableIT_UPDATE(TIM17);

my 4MHz output on TIM3 (CH4) stops working too.

[Kurt Alber]

Posted on February 22, 2018 at 08:46

The solution was the clearance of the FLAG UIE in TIM17->SR. I was stuck permanently in the IRQ routine.