What is the interrupt behavior in Cortex M3

Aamir,

In answer to your questions:

1) if the same interrupt is triggered after you have cleared the flag but before the interrupt has finished then the interrupt will finish processing, return, and then immediately be thrown back into the interrupt again. The interrupts would happen one after the other.

2) correct, assuming the high and low refer to the priority of the interrupt and not the number (keep in mind the lower the number the higher the priority, 0 has the highest priority)

3) if a higher priority interrupt comes in then it will preempt the current interrupt and the context will be switched to it and then be returned to the lower priority interrupt when it is finished. It would look like this

____

|

|

Low Priority Int

|

|

________

      |

      High Priority Int

      |

________

|

Finish Low Priority Int

|

____

Regards,

Austin

@ TI Austin:  Believe your verbage - and especially the amplifying drawing - make your response superb.  Well done - thanks...

Perhaps one slight addition - should the particular interrupt service be of great importance - upon entry to that "key interrupt service" - all interrupts can be disabled - insuring that this special interrupt is serviced w/out any disruption.  Last entry w/in this key interrupt service must then "re-enable" all interrupts.

Joseph Yiu, "The Definitive Guide to the ARM Cortex-M3, 2nd Edition"

http://store.elsevier.com/product.jsp?isbn=9781856179638

Thanks Austin for the explanation.

Can you please provide some example code to demonstrate how to increase the priority of Interrupt so that it pre-empts the current interrupt and then NVIC restores it ?

Thanks,

Sanchit Mehra 

Hello Sanchit,

You may want to go through the following TIVAWare example

C:\ti\TivaWare_C_Series-2.1.0.12573\examples\boards\ek-tm4c123gxl\interrupts

Regards

Amit

Ok . 

Thanks Amit .

Now, i am setting the following priorities 

ROM_IntPrioritySet(INT_GPIOQ1,0x40); // low priority
ROM_IntPrioritySet(INT_TIMER2A,0x00); // high priority

So, if the Timer(timeout interrupt) interrupt comes in between the GPIOQ1 Pin interrupt , then pin Interrupt should be Pre-empted and TIMER2A Interrupt should be handled first and then Pin Interrupt should be restored.

Am I right ?

Thanks,

Sanchit

Hello Sanchit

Yes, I confirm your statement.

Regards

Amit

Hello Amit, 

Actually I am starting the timer in between the GPIOPin Q1 interrupt routine.

int timerdone = 0;

void GPIOPIntHandler(void) // interrupt handler for GPIO event

{ 

ROM_IntEnable(INT_TIMER2A);
ROM_TimerIntEnable(TIMER2_BASE, TIMER_TIMA_TIMEOUT);
ROM_TimerEnable(TIMER2_BASE, TIMER_A); // enable the timer in the routine

while(timerdone == 0) {UARTprintf("waiting for timer interrupt");  ......}

}

the Timer interrupt doesnot execute in between the GPIOINT routine ..

void Timer2IntHandler(void)

{

UARTprintf( "in timer routine \n";

timerdone = 1;....

}

Please suggest.

Thanks,

Sanchit

Hi, 

I just printed the following things:

UARTprintf("\nPriority of Timer 2A is %d\n",ROM_IntPriorityGet(INT_TIMER2A));
UARTprintf("\nPriority of GPIOQ1 is %d\n",ROM_IntPriorityGet(INT_GPIOQ1));
UARTprintf("\npreemtable priority bits is %d \n",ROM_IntPriorityGroupingGet());
UARTprintf("\n Priority Masking : %d \n",ROM_IntPriorityMaskGet());

Priority of Timer 2A is 0

Priority of GPIOQ1 is 128

preemtable priority bits is 7

Priority Masking : 0

Masking is 0, So Will there be any effect on Interrupt prioritization ?