MQX Watchdogs for Multiple Tasks

brentwilliams — Tue, 28 Jan 2014 20:40:08 GMT

Hi David,

The MQX RTOS documentation states the following:

The MQX watchdog component provides a software watchdog for each task. If a single

task starves or runs beyond certain timing constraints, the watchdog provides a way to

detect the problem. Initially, the task starts its watchdog with a specific time value, and if

the task fails to stop or restart the watchdog before that time expires, MQX calls a

processor-unique, application-supplied expiry function that can initiate error recovery.

Before a task can use the watchdog component, the application must explicitly create it

by calling _watchdog_create_component() with the interrupt vector of the periodic

timer device and a pointer to the function that MQX will call, if a watchdog expires.

When first reading this it states “the interrupt vector” implying that you can have multiple watchdog expiry functions (one for each task) associated with BSP_TIMER_INTERRUPT_VECTOR.

But this is not the case, the watchdog component can register only one function to the interrupt vector. The second time it fails because it was initialized already.

_lwsem_wait((LWSEM_STRUCT_PTR)(&kernel_data->COMPONENT_CREATE_LWSEM));
if (kernel_data->KERNEL_COMPONENTS[KERNEL_WATCHDOG] != NULL) {
_lwsem_post((LWSEM_STRUCT_PTR)(&kernel_data->COMPONENT_CREATE_LWSEM));
_KLOGX2(KLOG_watchdog_create_component, MQX_OK);
return(MQX_OK);
} /* Endif */

I am not sure how this would work for multiple tasks with just the one associated timer interrupt vector (BSP_TIMER_INTERRUPT_VECTOR)??

If you have multiple tasks running and they are all "petting" the same watchdog timer, one task could be stuck while others are just fine and refresh the watchdog. As a result, a stuck task will not cause the watchdog to go off.

Any insight would be appreciated.

Thanks,

Brent

Re: MQX Watchdogs for Multiple Tasks

DavidS — Thu, 30 Jan 2014 17:26:41 GMT

Hi Brent,

It has been awhile since I have played with the MQX watchdog.

MQX has a capability to implement task watchdog timers (reference ~mqx/examples/watchdog) that will ensure task do not fail and if they do then an ISR routine is called and decision as what to do can be done (ex: reset device, kill task and try reset, log stuff, etc.). The example simply logs to terminal which task failed. I enhanced the code to work with multiple tasks as originally it was working with only one.
I've attached that example. Note it is old and I last ran it on a ColdFire using MQX3.6 so it may need tweaking.

Regards,

David

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MQX Watchdogs for Multiple Tasks

Re: MQX Watchdogs for Multiple Tasks