After a code review, I think I now know what is going on there. My program contains two parts, a user-space rt_task, and a kernel-space task. While the user-space task is waiting for its next release point (rt_task_wait_period), the kernel task calls rt_task_suspend and rt_task_resume to suspend and resume that user-space task occasionally, which should not be done. I don't know whether rt_task_suspend or rt_task_resume causes the user-space rt_task_wait_period() to return prematurely, but it seems that where the cause is. And after I fixed this bug, the problem was gone.
Thanks a lot! ________________________________ From: Philippe Gerum <[email protected]> To: Tom Z <[email protected]> Cc: "[email protected]" <[email protected]> Sent: Friday, 26 April 2013 5:16 AM Subject: Re: [Xenomai] rt_task_wait_period returns -11 (-EAGAIN) On 04/23/2013 07:42 PM, Tom Z wrote: > Hi Philippe, > > Thanks for answering my previous question. However, I encountered > another one regarding rt_task_wait_period(). NowI fixed a problematic > parameter in rt_task_set_periodic(), and add the checking of the return > values of rt_task_wait_period() and rt_task_set_periodic(). I use > rt_task_set_periodic()to set a period of 500 ms for a rt_task, and call > rt_task_wait_period() later. It seems that sometimes > rt_task_wait_period()works good, but sometimes it just returns 0 > immediately. Here is what my code looks like: > > unsigned long overrun; > RTIME release_time; > > if (0 != rt_task_set_periodic(NULL, TM_NOW, 500000000){ > rt_printf("Error\n"); > } > .... > while (1){ > release_time = rt_timer_read(); > //Store release_time in an array for offline analysis > //Some computation taking about 100 ms > if (0 != rt_task_wait_period(&overrun)){ > rt_printf("Error\n"); > } > } > > > I noticed that, during the program's execution, no "Error" was printed, > but some consecutive values of release_time is about 100 ms which is the > computation time and far less than the period 500 ms. > > This problem seems weird to me. Did I possibly overlook something? > What does "some consecutive values" mean in this report, what about the other values? Also, how do you observe this behavior, by looking at the pace of rt_printf's output? If so, I would suggest to log all release times and wait_period() return codes in an array, performing the sampling loop silently. Then check the array for spurious samples, i.e. error returns or weird intervals between samples. -- Philippe. _______________________________________________ Xenomai mailing list [email protected] http://www.xenomai.org/mailman/listinfo/xenomai
