Re: NI 6602 - comedi_data_read(..) takes 4ms (RTAI 3.3)

Hello Derek,

I think this could just be very much helpful.

Infact, I just acquired a slightly older computer with less integrated
devices.
Tomorrow or during next week I will install the same setup on that machine
and see whether things work better. Also, I will probably remove the
graphics
card alltogether if a similiar 4ms issue is detected.

In any case, it seems more evident that this is a hardware/RTAI issue
than Comedi. So I should probably turn to that mailing-list.
   However, I will of course reply to this thread after further testing and
report
if everything works well, and hopefully to confirm that there's no issues
with
the NI 6602.

regards,
Camino



On 3/29/06, Derek Foreman <Derek.Foreman_at_nrc-cnrc.gc.ca> wrote:
>
> This might not be at all helpful, but I've seen fairly large latencies
> created by lots of hardware...
> (I use different cards, and one of my acquisition cards isn't driven by
> comedi at all)
>
> Specifically:
> an on board (but still on the same bus as the pci slots, disgusting) sata
> chip (on chipset IDE controller has no such issue).
>
> an intel pci gigabit ethernet card on the same bus as the acquisition
> cards (removed, on chipset 100mbit NIC is tolerable.)  I suspect a lot of
> on-board chips are on the pci bus with the slots and can cause latency.
>
> an agp geforce 4 card.  I had to disable all textual output as well as the
> console blanker to fix this.
>
> To me, untolerable latency is > 50uS in servicing the NMI.
>
> The graphics card was creating several hundred, maybe several thousand uS
> delays.
>
>
> On Wed, 29 Mar 2006, janne wrote:
>
> > Hello Arno,
> >
> > The procedure is to simply call rt_get_cpu_time_ns(); in the beginning
> of
> > the task,
> > immediately before and after reading encoder values, and subracting the
> > difference.
> > Same thing with Analog out,  and finally at the end of the task for
> total
> > Task execution-time.
> >
> > Another interesting issue was found. Reading the encoder also has
> ~~200us
> > execution time
> > every two seconds if the ethernet cable is connected during boot time.
> The
> > analog out or the
> > rest of the task's execution times are not affected.
> >   It really seems like there's a conflict of some sort. Whether this has
> to
> > do with the comedi-driver
> > or the hardware, I do not know.
> >   I will e-mail you a graph shortly showing the behavior of the task.
> (If
> > someone else is interested to
> > see it, notify me).
> >
> > Worth mentioning is that unlike the regular 2 second ~~200us execution
> > times, the really nasty 4ms
> > delays are not regular at all.  But usually comes 1-3 times within 20
> > seconds without much pattern.
> >
> > Regards,
> > Camino
> >
> > On 3/28/06, Stienen, A.H.A. (CTW) <a.h.a.stienen_at_utwente.nl> wrote:
> >>
> >> janne wrote:
> >>> I'm running a single task (about 4KHz) that reads encoder values and
> >>> ouputs an analog signal.
> >>> When running for 20 seconds, there are usually a few instances ( 1 -
> 3)
> >>> where reading values
> >>>  from the encoder takes about 3800 - 4000 us. Which is, of course
> awful.
> >>
> >> How do you measure this? What is the procedure?
> >>
> >> FWIW, I'm using the same card and haven't noticed similar problems.
> Then
> >> again, I haven't looked either...
> >>
> >> Arno.
> >> --
> >>    ____
> >>   /  |_| <<< IR. ARNO H.A. STIENEN >>>
> >> |_ O  | Biomechanical Engineering | http://www.bw.ctw.utwente.nl
> >> |_|__/  a.h.a.stienen_at_utwente.nl  | +31-(0)53-489-4778
> >> UTwente "There are alternatives: Firefox, Thunderbird & OpenOffice!"
> >>
> >>
> >>
> >
>