--- In "hans.schillstrom" <> wrote:
>
>
>
>
>
>
> --- In "j.chitte" <j.chitte@> wrote:
> >
> >
> >
> >
> >
> > --- In "mccarl1978" <mccarl1978@> wrote:
> > >
> > >
> > > >
> > > > The one big downside is that it seems to be set (non adjustable) at
> > > > +/-10V and I need 0-5V
> > > >
> > > > The readme says it's set in the code but at a first reading I can't see
> > > > where. Anyone looked at this?
> > > >
> > >
> > > The lines that you are looking for are lines 168 & 188 of adc_hwtimer.c
> > >
> > > Check adc_hwtimer.h for the defines that you can use for different
> > > ranges, etc.
> > >
> > > Cheers
> > > Phil
> > >
> >
> > Thanks , it was a great help knowing that's all I needed to look at.
> >
> > I now have the platform and /dev drivers and my userland C code to work
> > with.
> >
> > Am I correct in thinking that the primary limit on sampling freq is the
> > timer resolution? It seems it can't do much better than 10kS/s on single
> > channel readings.
> >
> > What would be the best strategy for approaching the 100k limit of the MAX
> > chip? I know I won't get there but I'm interested in the limits of the
> > board.
> >
> > Oh, and thanks for a nice clean example of how to write a kernel driver. ;)
> >
>
> The timer resolution on the EP93xx is normally 508kHz for Timer1-3, and
> that's not the limit in this case.
>
> My experience from the board is that the jitter will be 1-15ms
> The kernel will turn off interrupts for several ms, (up to 15ms on a 7250
> board with 2.6.29 kernel)
> The requirements in my case was a sampling rate of 2.5 kHz with jitter less
> than 200us. I guess that you can figure it out the limitations of the kernel.
>
> I implemented Xenomai (a Real time Linux patch) to the 7250 board with
> dynamic timer ticks. It works great, with an interrupt latency of ~20-120us
> Right now I'm running Max197 at 5kHz with RMS calc on 4 channels and it gives
> a CPU load of 1.5%.
>
> Regards
> Hans
>
Thanks for the info. It's interesting to see what others have managed to get
out of the board.
MAX197.pdf says:
6us conversion time , 100ksps sample rate.
TS manual states:
After the write cycle to location 0x10F0_0000, the MAX197 completes the A/D
conversion in about 12 mS
Three orders of magnitude slower that the chip spec. (Did they mean 12us ?!)
Your results on jitter suggest it can not sample reliably faster then 8ksps
(120us) , a Nyquist freq of 4kHz even with a RT layer.
That's rather disappointing.
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