Disabling interrupts and clearing flags (TIM8 CC4) - Only working when interrupts are enabled?

[Tobe]

I have quite a complicated case, where a interrupt is beeing executed, allthough it has been disabled, and its flag beeing cleared. At the same time interrupts are disabled, and i put a few nops in between just to rule out any delay related issues. The disabling of the interrupt works, but there is just one afterwards that i cant get rid of.

For now i just would like to know, if anyone has any idea if the title can be answered with yes. (And if there is a explanation why that is)

I would have liked to try a minimal code, but its quite complicated and i am afraid the error can then not be reproduced. Timers are interconnected too.

[waclawek.jan]

If you disable the interrupt at the source (e.g. in TIMx_DIERx), it takes time until this gets propagated into NVIC.

There may be a strange effect with the interrupt "reappearing" in NVIC, if it was cleared too soon after disabling the interrupt source.

JW

[Tobe]

This is how i clear it:

CLEAR_BIT(TIM8->DIER, TIM_DIER_CC4IE);

30 NOP´s

TIM8->SR = ~TIM_SR_CC4IF;

30 NOP´s

other code

SET_BIT(TIM8->EGR, TIM_EGR_COMG); //should not matter here

delayMicros(2);

When i enable interrupts before the delay, the interrupt does not get fired again, if i enable interrupts after, it does get fired again. See the picture for timing illusatration:

• PC4 is the actual clearing (first 5 lines of code above).
  
• PB11 is the problem interrupt
• Pink lines show interrupt times
• PA12 is the interrupt, that (should) disables the problem interrupt
• Ignore the "IRQ Disabled" channel, as it has some issue and is not valid

[waclawek.jan]

There is no direct relationship between commutation event and CC4 event, so it can't be judged from this description without knowing your entire program.

JW

[Tobe]

Any ideas what i could look into? What registers, or what tactic could be done?

What about the enabling of interruts, why does it make a difference of when the are enabled?

[Tobe]

Allthough your link is not the exact problem i have (i think), it helped me (reading pending states) to get further: clearing the TIM_SR_CC4IF flag did not clear the pending interrupt, i had to clear the pending interrupt too.

Is this something that has to be done in general? I did not stumble upon this issue yet with my other interrupts.

[Tobe]

I have now finished my investigation:

It is, as i expected, and wrote in the title of this topic:

In order for the pending status to be cleared with clearing the TIM_SR_CC4IF flag, interrupts have to be enabled at the same time. This also applies to reading the TIM_SR_CC4IF register.

That is NOT something i would expect. Usually i would disable interrupts, and then clear flags, to have a clean state of my program.

NOTE: It is necessary to have enabled interrupts in general, AND the CC interrupt itself, in order for the reading and clearing of the CC4IF flag to work properly!

I went down the rabbit hole, and i was there for quite a few days...

Huge thanks @waclawek.jan for pushing me into the right track, and using the array to debug the pending state!

Here the code as it was last used by me:

//__enable_irq();
	//while(READ_BIT(TIM8->SR, TIM_SR_CC4IF));	// Wait for flag to cause issue //TODO: Debug remove

	//IRQ_DISABLE_SAVE_PREV
	NVIC_EnableIRQ(TIM8_CC_IRQn);

	SEVEN_NOPS
	stateArray[2] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);

	TEST_CLEAR_TIM8_CC4_IRQ_DIS_ON
	CLEAR_BIT(TIM8->DIER, TIM_DIER_CC4IE);	// Disable interrupts (from ADC trigger) for kind of sine wave generation

	SEVEN_NOPS
	stateArray[3] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);

	TIM8->SR = ~TIM_SR_CC4IF;				// Clear any pending interrupts that were already pending.

	stateArray[4] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);
	SEVEN_NOPS
	stateArray[5] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);

//	NVIC_ClearPendingIRQ(TIM8_CC_IRQn);
//
//	stateArray[6] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);
//	SEVEN_NOPS				// Account for delay, that a signal could arrive after clearing the pending interrupt.


	stateArray[7] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);




	if(millis() > 100)
		stopNow = true;
	updateDuty();


	delayMicroseconds(6);	// delay and test if interrupt cleared
	TEST_CLEAR_TIM8_CC4_IRQ_DIS_OFF
	//__enable_irq();
	NVIC_EnableIRQ(TIM8_CC_IRQn);
	stateArray[8] =  NVIC_GetPendingIRQ(TIM8_CC_IRQn);

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