Posted on November 24, 2012 at 15:09Hi,
please have a look at the following code (STM32F407):
volatile long long vllPosition;
void TIM1_UP_TIM10_IRQHandler(void){
... do interrupt stuff ...
vllPosition ++;
... do interrupt stuff ...
}
int main( void){
... do some init stuff ...
for(;;){
... do the loop stuff ...
if( ...){ // from time to time it is necessary to assing some value to llPosition
vllPosition= llSomeValue;
}
... do the loop stuff ...
}
}
As long long is 64 bit, the access to vllPosition is non-atomic. So an assignment like vllPosition= llSomeValue is dangerous: it might be interrupted by my interrupt and then the complete thing will mix up.
In an easy access, I would like to disable the interrupt temporarily. There would be 3 different possibilities I see:
1.:
NVIC_DisableIRQ( TIM1_UP_TIM10_IRQn);
vllPosition= llSomeValue;
NVIC_EnableIRQ( TIM1_UP_TIM10_IRQn);
2. (The TIM1_UP_TIM10_IRQ is entered exclusively by the UIE):
TIM1->DIER = 0;
vllPosition= llSomeValue;
TIM1->DIER = TIM_DIER_UIE;
3.
__disable_irq();
vllPosition= llSomeValue;
__enable_irq();
Is any of these methods 100% safe (of course I would prefer method 1 or 2, as 3 disables all interrupts)? (Due to the prefetch delay I am not sure about this - I did not find a guarantee anywhere and it is difficult to decide only by testing). (Or would I need some more elaborate methode to ensure this in a secure way, e. g. with semaphores or so?)
#stm32
