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ARM Cortex-A9 FreeRTOS_IRQ_Handler

Posted by kamejoko80 on February 20, 2017

Hello everyone,

Regarding to ARM cortex-a9 porting, I see the IRQ handler as below code :

FreeRTOSv9.0.0FreeRTOSSourceportableGCCARM_CA9portASM.S

~~~ .align 4 .type FreeRTOSIRQHandler, %function FreeRTOSIRQHandler:

...

/* Call the interrupt handler. */
PUSH	{r0-r3, lr}
LDR		r1, vApplicationIRQHandlerConst
BLX		r1
POP		{r0-r3, lr}
ADD		sp, sp, r2

CPSID	i
DSB
ISB

.... ~~~

This code intends to allow nested interrupt but IRQ enable instruction "CPSID i" is bellow application IRQ handler, I think this is not correct. In order to higher priority IRQ can preamt lower priority IRQ, IRQ enable instruction should be placed before application IRQ handler.

~~~

...

/* save registers */ PUSH {r0-r3, lr}

CPSID	i
DSB
ISB

/* Call the interrupt handler. */
LDR		r1, vApplicationIRQHandlerConst
BLX		r1

POP		{r0-r3, lr}
ADD		sp, sp, r2

.... ~~~

Please correct me if I'm wrong.

Thanks and Best Regards, Phuong Dang


ARM Cortex-A9 FreeRTOS_IRQ_Handler

Posted by rtel on February 20, 2017

This code intends to allow nested interrupt but IRQ enable instruction "CPSID i" is bellow application IRQ handler, I think this is not correct. In order to higher priority IRQ can preamt lower priority IRQ, IRQ enable instruction should be placed before application IRQ handler.

The IRQ enable instruction is in the application IRQ handler. It is done that way to allow the application writer to decide if they want an interrupt to be nestable or not. CPSID i is disabling the IRQ again, not enabling it, which is why it appears after the application handler.


ARM Cortex-A9 FreeRTOS_IRQ_Handler

Posted by kamejoko80 on February 20, 2017

Hello FreeRTOS,

Got it,

Sorry for my miss reading regarding to CPSID i command. Thanks so much for your quick reply.

Best regards


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