Posted on November 30, 2017 at 10:53Hi everyone!
I've been recently using the LPTIMER, along with the compare and autoreload interrupts. Microcontroller is an STM32L073.
It has been working fine, mostly, but I realized that if I remove a delay (which used to be a printf to uart) I get thousands of interrupts one after the other.
To be honest I don't see how I could get so many interrupts if flags are being cleared, and what does it have to do with the delay (race condition?).
Let me show you some code:
This is the init function. Default values for autoreload are 1 second (32767) and half of that for the compare.
// Initializes the Low Power Timer with default values. Timer is ready to be used after calling this function.
void lpTim_Init(void)
{
//Enable clock to the Low Power Timer
RCC->APB1ENR |= RCC_APB1ENR_LPTIM1EN;
//Settings can only be changed when the LPTIM is disabled
LPTIM1->CR = 0x00000000;
//Set the Configuration Register
//Encoder mode disabled, Registers updated after write access, normal polarity,
//Set-once deactivated, trigger while running is ignored, Software trigger selected,
//ext_trig_0 selcted (though ignored), Divide by 1 prescaler, No digital filter for trigger,
//No digital filter for external clock, rising edge of clock polarity, use internal clock
LPTIM1->CFGR = 0x00000000;
//Clear interrupt clear register from previous use
LPTIM1->ICR |= 0x3F;
//Enable LPTIM. LPTIM ready to start
LPTIM1->CR = LPTIM_CR_ENABLE;
//Set the autoreload register to its default value.
//Must only be modified when the LPTIM is enabled
LPTIM1->ARR = LPTIM_DEFAULT_ARR;
//Set compare value
//Must only be modified when the LPTIM is enabled
LPTIM1->CMP = LPTIM_DEFAULT_CMP;
//Autoreload match and compare interrupt enable
LPTIM1->IER = LPTIM_IER_ARRMIE | LPTIM_IER_CMPMIE;
//Set the interrupt priority
NVIC_SetPriority(LPTIM1_IRQn,0);
//Enable interrupt
NVIC_EnableIRQ(LPTIM1_IRQn);
TRACE_DBG_H('LPTIMER initialized\n');
}
And this is my interrupt handler, where I put some pin up/down just to see the interrupts being triggered.
//Interrupt handler
void LPTIM1_IRQHandler(void)
{
GPIOH->BSRR = GPIO_PIN_0;
//If there was an autoreload
if(LPTIM1->ISR & LPTIM_ISR_ARRM)
{ //If the interrupt was enabled
if(LPTIM1->IER & LPTIM_IER_ARRMIE)
{ //Clear interrupt bit
LPTIM1->ICR = LPTIM_ICR_ARRMCF;
//Timer_OverflowCallback();
}
}
//If there was a compare match
if(LPTIM1->ISR & LPTIM_ISR_CMPM)
{ //If the interrupt was enabled
if(LPTIM1->IER & LPTIM_IER_CMPMIE)
{ //Clear interrupt bit
LPTIM1->ICR = LPTIM_ICR_CMPMCF;
//Timer_CompareCallback();
}
}
GPIOH->BRR = GPIO_PIN_0;
}
If I do this, it works fine.
void main(void)
{
//Some init..
lpTim_init();
//Start timer
LPTIM1->CR = LPTIM_CR_ENABLE | LPTIM_CR_CNTSTRT;
while(1);
}
If I do this I get a bazilion interrupts one after the other:
void main(void)
{
//Some init..
lpTim_init();
LPTIM1->ARR = 28000; //Random value 28000
//Start timer
LPTIM1->CR = LPTIM_CR_ENABLE | LPTIM_CR_CNTSTRT;
while(1);
}
But if I do this, it works fine again:
void main(void)
{
//Some init..
lpTim_init();
HAL_Delay(1);
LPTIM1->ARR = 28000; //Random value 28000
//Start timer
LPTIM1->CR = LPTIM_CR_ENABLE | LPTIM_CR_CNTSTRT;
while(1);
}
Any clues as to why I might have this behavior? Seems pretty strange to me. Maybe doing LPTIM1->ARR modifications right after interrupt enable ruins everything?
Cheers, and thanks for your help!
Andrés
