Re: How to tune one shot time period

Paolo,

A little bit of the set up and function calls are below. This is based 
on the vgttime sample code from rtai.dk.
long ticks_per_second=0;
   ticks_per_second = (long)nano2count((RTIME)(1000000000));
....
   rt_set_oneshot_mode()
....
   start_rt_timer(0);
....
rt_task_make_periodic(hrttsk, rt_get_time() 
/*+(RTIME)(period*ticks_per_second+.5)*/, (RTIME)(period*ticks_per_second));
....
   time=rt_get_time()/ticks_per_second;

During initialization, an offset between the timer and the system time 
is calculated and applied thereafter, so system and counter times start 
close and drift.

Randy

On 12/18/2015 04:49 PM, Paolo Mantegazza wrote:
> How do you set the period, i.e:  what RTAI timing function do you use for that?
> Paolo
> ________________________________________
> From: Rtai [[email protected]] on behalf of Randy Ricklefs [[email protected]]
> Sent: Friday, December 18, 2015 7:37 PM
> To: [email protected]
> Subject: [Rtai] How to tune one shot time period
>
> Hi,
>
> I am working on a project that requires a 100msec loop that has a drift
> of no more than about 100usec per hour. I am using the oneshot mode with
> RTAI 4.1 with kernel 3.10.32 on an i7 computer, and the 100msec period
> is very stable (+/- a few usec), but compared to the system time and UTC
> is actually larger than 100msec by an amount than creates a drift rates
> close to 10msec every 10 or 20 minutes. I have tried varying the 100msec
> period by small amounts to compensate, but the results are not
> satisfactory. I understand there is a method of calibrating the timer
> used for oneshots, but I have not found documentation of the procedure.
> Once calibrated, will the period remain stable, or are there temperature
> variations? Any help would be appreciated!
>
> Thanks!
>
> Best regards,
> Randy Ricklefs
> _______________________________________________
> Rtai mailing list
> [email protected]
> https://mail.rtai.org/cgi-bin/mailman/listinfo/rtai


-- 
  -----------------------    Randy Ricklefs    ------------------------
                        [email protected]
      Center for Space Research,  The University of Texas at Austin
                            Austin TX 78712

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