[freertos - Open Discussion and Support] vApplicationStackOverflowHook cannot wake ...

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By: wella

Hi,

please, could someone help me, what I am doing wrong? I have created two tasks,
the first is used to generate stack overflow the latter to detect it. In the
function vApplicationStackOverflowHook, I am trying to send something (even
uninitialized, does not matter) to the queue. The variable pxHigherPriorityTaskWoken
is pdTRUE and portYIELD_FROM_ISR() is called. However the
vApplicationStackOverflowHook is called again and again. How should I end the
vApplicationStackOverflowHook to wake up the function detect_stack_error?

Thank you for your advices.

Regards
Martin

ARM7 - LPC2478 - v7.0.2

[code]xQueueHandle xQueue;
void stack_error( void * pvParameters ) // priority normal
{
uint32_t stack[40];

for (int i = 0; i < 50; ++i)
{
stack[i] = i;
}

while (1)
{
vTaskDelay(1);
}
}


void detect_stack_error( void * pvParameters ) // priority highest
{
xQueue = xQueueCreate(10, sizeof(unsigned char));
unsigned char a;
while (1)
{
xQueueReceive(xQueue, &a, portMAX_DELAY);
__asm ("NOP\n");
}
}

void vApplicationStackOverflowHook(void *pxTask, char *pcTaskName)
{

(void)pxTask;
portBASE_TYPE pxHigherPriorityTaskWoken;
unsigned char pvItemToQueue;
xQueueSendFromISR( xQueue, & pvItemToQueue, &pxHigherPriorityTaskWoken );

if(pxHigherPriorityTaskWoken)
portYIELD_FROM_ISR();
}
[/code]

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By: richard_damon

If you are not running on a system with an MMU, once you have experienced a
stack overflow, the system may well be now in an unstable state and not able
to continue.

I am also not sure what parts of the API are allowed to be called from the stack
overflow routine, and I suspect trying to force a task switch may not be allowed
there, as the stack check is happening within the task switch routine.

Normally the overflow hook will be code to somehow output an error message somewhere
if possible with primitive code, and then restart the processor.

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By: richardbarry

Generally, unless you are using an MPU port, you cannot recover from a stack
overflow. When you have an MPU, you get notification of the stack overflow
before any corruption happens as a trap is triggered as soon as a write outside
of the region allocated to the stack is attempted. Most ports don't use an
MPU, and you only know a stack overflow has happened some time after it has
happened - and at that point you don't know what the system state is so all
you know is you know nothing. Generally a stack overflow will corrupt a TCB,
so the task you are trying to yield from is already corrupt. Even if you are
lucky enough that something sensible happens, you will just re-enter the context
switch and detect the stack overflow again.

Regards.

Also consider that the stack overflow is called from the context switch mechanism.
You cannot attempt to re-enter the context switch by requesting a context switch
when you are already in a context switch (if that makes any sense at all ;o).