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ISR handling with PIOs

Posted by Nobody/Anonymous on May 10, 2005

I am having problems with getting the PIO interrupt to work properly. I have made a wrapping function in assembler and the interrupt is called properly, but when processor is about to leave the ISR and the portRESTORE_CONTEXT is called I get a data abort exception. Why is this?? My ISR is pasted below:

__arm void pio_ISR( void )
portCHAR cContextSwitchRequired;

int dummy;
dummy=dummy; //Suppress compiler warning
//* Read the output state
if ( (AT91F_PIO_GetInput(AT91C_BASE_PIOA) & INPUT_SERVO2_CAP) == INPUT_SERVO2_CAP); //Don't do anything, rising edge
else //Falling edge -> capture value in
measure.duty_channel_2 = TimerBaseCPWM->TC_CV;

cContextSwitchRequired = pdFALSE;

portEND_SWITCHING_ISR( ( cContextSwitchRequired ) );

/* End the interrupt in the AIC. */

Interrupt initialization:

//* set the interrupt by software

Wrapping file:


; Wrapper for the USB interrupt service routine. This can cause a
; context switch so requires an assembly wrapper.

; Defines the portSAVE_CONTEXT and portRESTORE_CONTEXT macros.
#include "ISR_Support.h"


portSAVE_CONTEXT; Save the context of the current task.

blpio_ISR; Call the ISR routine.

portRESTORE_CONTEXT; Restore the context of the current task -
; which may be different to the task that
; was interrupted.


Thanks in advance!

RE: ISR handling with PIOs

Posted by Richard on May 11, 2005
I cannot see anything obviously wrong by looking at the code. Unfortunately I will not be able to try it until Sunday but here are a couple of pointers:

+ Could it be a stack problem? Try increasing the stack size a bit - or inspecting the stack in the debugger.

+ Currently the code is always set to pass false to portEND_SWITCHING_ISR. If you are not wanting to cause a context switch from within the ISR then you do not require any special syntax, and the standard IAR syntax can be used. You also then don’t then require the wrapper either (see the "interrupt service routines" section of http://www.freertos.org/portsam7iar.html for detail).

Even if you are intending on adding a context switch within the ISR at a later time it might be worth trying it without the wrapper to start with to check that there is nothing else wrong.

Let me know how you get on. If you are still having problems on Sunday I should be able to setup a test.


RE: ISR handling with PIOs

Posted by Nobody/Anonymous on May 12, 2005
I tried to increase stack size without success, when I try the standard syntax it will enter the ISR but never leave it. Problem seems to be that when it tries to leave ISR it jumps back to top of ISR. It seems like the stack pointer gets lost somewhere?!

RE: ISR handling with PIOs

Posted by Richard on May 12, 2005
Would it be possible to send me a small project that demonstrates the problem? The smallest amount of code that still has the problem, along with the IAR project file. I could then test to see if I can identify the solution.

If so please you the email address from the contact page of the FreeRTOS.org WEB site (r.barry at ...) as the SourceForge address will strip the attachment.


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