Re: [Xenomai-help] no-brainer realtime issue

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka wrote:
> Steven Seeger wrote:
> 
>>I have a xenomai userspace application that does the following:
>>
>>A thread of priority 90 toggles a bit (outb) to move a stepper motor.
>>
>>A thread of priority 10 updates the display once a second.
>>
>>The motor thread is periodic and uses rt_task_wait_period(). The display
>>thread just uses sleep(1).
>>
>>My question is this: the priority 90 thread is higher priority, and doesn't
>>do anything relating to linux system calls. Whenever the display thread
>>updates the display, the motor thread stalls momentarily.
>>
>>Any idea why this is?
> 
> 
> If your motor thread really looks like
> 
> while (1) {
> 	toggle_bit();
> 	rt_task_wait_period();
> }
> 
> you may suffer from contentions of the related bus towards your motor
> (what kind of interface do you use?).
> 
> To test this, just put some instrumentation around the toggle_bit()
> (take timestamps and look for abnormal delays). What frequency is your
> motor thread running at?
> 
> If there is more code in your loop, please post the program (or a
> simplified but still failing version).

Additionally, the output of /proc/xenomai/stat for a failing run might give some 
useful information.

> 
> Jan
> 
> 
> 
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-- 

Philippe.