Re: [Xenomai-core] Watchdog/Interrupt management

[Philippe Gerum <rpm@xenomai.org>]

ROSSIER Daniel wrote:
> Hi all,
> 
> I've a - probably small ;-) - issue regarding the way how the watchdog and interrupt management are working together.
> I'd like to implement a watchdog in a task to ensure that a task is well alive at periodic interval. For doing some tests, I've
> implemented a small ISR which interceipts the keyboard interrupts (IRQ 1). The ISR is simply doing some busy wait burning CPU time,
> but with a delay greater than the task period.
> I assume that the ISR locks the rescheduling procedure as it is stated in the API doc (BTW; many thanks for having solved the doc issue).
> So, the task switching is temporarly suspended and the watchdog should raise up an alarm after the ISR has been completed, right?
> It doesn't.

Because Adeos disables interrupts by default when calling an ISR from a non-Linux 
domain (like Xenomai's). You can re-enable them to get nested interrupts by doing 
this in your ISR:

unsigned long flags;

rthal_local_irq_sync(flags);
<spin>
rthal_local_irq_restore(flags);

> I've attached the code below (I've removed the function return check for readibility reasons, but all objects are fine).
> 
> Another question:  the ISR is called on behalf of the interrupted stack context: does it mean that the ISR always runs in the stack context of the highest priority task, i.e. the running task (assume no inversion priority), or could it in some cases the kernel stack context (if ADEOS is currently doing some interruptible stuff..)
> 

I-pipe Adeos versions always run interrupt handlers over the stack of the 
preempted context.

> Many thanks for your feedback.
> 
> Cheers
> Daniel
> 
> 
> -----------------------------------------------------
> #include <native/task.h>
> #include <native/intr.h>
> #include <native/alarm.h>
> 
> #define STACK_SIZE 8192
> #define MS         1000000
> 
> RT_INTR isrDesc;
> RT_TASK highPrioTask;
> RT_ALARM alarm;
> 
> int isrKbdHandler(struct xnintr* _idesc) {
> 
>   printk("#IRQKeyb\n\n");
> 
>   rt_timer_spin(100*MS); // Arg. in ns
>   return RT_INTR_CHAINED;
> }
> 
> void __exit cleanup_module (void) {
> 
>   rt_intr_delete(&isrDesc);
>   rt_task_delete(&highPrioTask);
>   rt_alarm_delete(&alarm);
> 
>   printk("Bye bye!\n");
> }
> 
> void alarmHandler(RT_ALARM *alarmDesc, void *cookie) {
>   printk("#ALERT:\n\n");
> }
> 
> void periodicTaskHigh(void *cookie) {
> 
>   while (1) {
>     rt_alarm_start(&alarm, 51, TM_INFINITE);
>     rt_task_wait_period();
>   }
> }
> 
> int __init init_module (void) {
> 
>   rt_timer_set_mode(MS);   /* So, one tick will be equal to 1 ms */
>   rt_intr_create(&isrDesc, 1, isrKbdHandler, NULL);
>   rt_alarm_create(&alarm, "ALARM", alarmHandler, NULL);
>   rt_task_create(&highPrioTask, "highPrioTask", STACK_SIZE, 10, 0);
> 
>   rt_task_set_periodic(&highPrioTask, TM_NOW, 50);
>   rt_task_start(&highPrioTask, periodicTaskHigh, NULL);
> 
>   return 0;
> }
> 
> MODULE_LICENSE("GPL");
> 
> -----------------------------------------------------------------------------------
> 
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-- 

Philippe.