Timer Update Interrupt clarification

[STuser2]

This is a line of code i don't understand, 

 /* Force the TIMx prescaler with immediate access (gen update event)
    */
    LL_TIM_SetPrescaler(TIMx, pHandle->HALLMaxRatio);
    LL_TIM_GenerateEvent_UPDATE(TIMx);

The code is part of the __weak void HALL_Init(HALL_Handle_t *pHandle) function

when the second line of code is executed does it mean that i get the interrupt timer over flow interrupt immediately. Please clarify. The TIM4 is configured in XOR / Hall mode.

[KnarfB]

The timer pre-scaler register is buffered. The pre-scaler value set in line 3 is only effective after an update event.

Line 4 generates that update event.

hth

KnarfB

[TDK]

> does it mean that i get the interrupt timer over flow interrupt immediately

Generating an update event will cause an interrupt if the update interrupt is enabled.

[STuser2]

Thank you for your time and clarification

If i verify the complete code (MCSDK) for enabling the interrupts 

/* Force the TIMx prescaler with immediate access (gen update event)
    */
    LL_TIM_SetPrescaler(TIMx, pHandle->HALLMaxRatio);
    LL_TIM_GenerateEvent_UPDATE(TIMx);

    /* Clear the TIMx's pending flags */
    WRITE_REG(TIMx->SR, 0);

    /* Selected input capture and Update (overflow) events generate interrupt */

    /* Source of Update event is only counter overflow/underflow */
    LL_TIM_SetUpdateSource(TIMx, LL_TIM_UPDATESOURCE_COUNTER);

    LL_TIM_EnableIT_CC1(TIMx);
    LL_TIM_EnableIT_UPDATE(TIMx);
    LL_TIM_SetCounter(TIMx, HALL_COUNTER_RESET);

    LL_TIM_CC_EnableChannel(TIMx, LL_TIM_CHANNEL_CH1);
    LL_TIM_EnableCounter(TIMx);

The update interrupt is enabled in line 15. So, i really don't understand why line 4 is written? Does the reason is as suggested by @KnarfB is to update the pre-scaler but still not generate the interrupt as the interrupt is not enabled. Please clarify.  

[TDK]

Line 4 is written to do the thing it says it does in the comments.

/* Force the TIMx prescaler with immediate access (gen update event)
    */

In other words: to update the prescaler. event is generated because prescaler is preloaded.

[STuser2]

But the interrupt is not enabled, does it go to the interrupt as well? Please help.

[TDK · Accepted solution]

If the interrupt is not enabled, it won't go to the interrupt. It doesn't need to enter an interrupt to reset the prescaler.

Are you debugging a larger problem? What is the larger context here? Why are we talking about the interrupt at all?

[STuser2]

Thank you for the clarification, at present i am trying to understand the code of how input capture works and the speed measurement of the motor, as per the user manual the pre-scaler will be adjusted based on the speed of the motor.

After your explanation i can understand that the pre-scaler register value will be loaded into the pre-scaler buffer after the update event and it is not required to generate interrupt. I was of the impression that event always causes an interrupt.    

[waclawek.jan]

> I was of the impression that event always causes an interrupt.

As @TDK said above, if the interrupt is enabled, it will; if it's not enabled, it won't.

It will set TIMx_SR.UIF, though, so you want to clear this bit before interrupts are enabled.

Read the TIM chapter in RM.

JW