AnsweredAssumed Answered

Interrupt pending registers not cleared

Question asked by carter.bob on Dec 20, 2012
Latest reply on Dec 23, 2012 by knik
I have a number of switches which generate interrupts. When I Flick switch A it goes from High to Low
and the A interrupt occurs(EXTI_PR is now 0x00000200 as expected). I then clear the pending register (EXTI_PR is now 0x00000000).
At this time switch A is still at low which is what I require.

Now while switch A is still low, I switch B from High to Low. Instead of entering the B interrupt routine,
which is what I expect, the processor still enters the A routine. I can understand this because when I
check EXTI_PR, its value is 0x00000600. How can I avoid this situation? I need to keep A switched low while
B is switched. I would not have expected this as the interrupts are edge triggered. What is keeping the pending registers
from being properly cleared?

The pending register only changes to 0x00000400 when I switch A on and off. When I activate the switches by
flicking them ON and OFF, the interrupts behave accordingly. However, my system doesn't allow this.

I appreciate any help.


  /* Configure PC9 pin as input floating */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9|GPIO_Pin_10;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOC, &GPIO_InitStructure);
  /* Connect EXTI0 Line to PC9 pin */
  SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOC, EXTI_PinSource9);
  /* Connect EXTI0 Line to PC10 pin */
  SYSCFG_EXTILineConfig(EXTI_PortSourceGPIOC, EXTI_PinSource10);
  /* Configure EXTI9 line */
  EXTI_InitStructure.EXTI_Line = EXTI_Line9;
  EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt;
  EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Falling;
  EXTI_InitStructure.EXTI_LineCmd = ENABLE;
  /* Configure EXTI10 line */
  EXTI_InitStructure.EXTI_Line = EXTI_Line10;
  /* Enable and set EXTI4_15 Interrupt */
  NVIC_InitStructure.NVIC_IRQChannel = EXTI4_15_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelPriority = 0x00;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;


void EXTI4_15_IRQHandler(void)
   if(EXTI_GetITStatus(EXTI_Line9) != RESET)        
     printf("\n\r Interrupt A");
   else if (EXTI_GetITStatus(EXTI_Line10) != RESET)
     printf("\n\r Interrupt B");