On Sun, 16 Sep 2007, fabianmejia wrote:
> Hi All,
>
> I am under development of a capture system. I need to sample about
> 200Hz. That is, about sampling each 0.005 seconds.
>
> I have it working using the Jim Jackson's adc_logger.
>
> Unfortunatelly, this can't accomplish the job as it's accurate about 10ms.
>
> So, I decided using gettimeofday. Oh surprise!!! It doesn't work
> properly. microsecond precision? Forget about it. Readings give me
> mumbers like this:
>
> 510000
> 530000
> 550000
>
> It sounds like 10msec precision.
It is. If the HZ value for the kernel is 100 then the timing resolution
(not accuracy by the way :-) is 10ms.
One option would be to recompile the kernel with a higher HZ value.
The kernel arranges for a regular clock tick at this freq. and uses the
tick for updating system timers, scheduling etc. So beware, upping the HZ
value will up the system load. A value of 500 may be ok for your purposes.
another option is to use the ADC kernel driver by Phillip McCarley. It
uses a spare hardware counter to provide timing for doing repetitive
readings. Phil reckons it will do upto 8KHz. It used to be in the files
section of the group. If not there anymore just ask on list.
> Next step, checking the TS7000 group. I downloaded the file:
> linux24_ts8-lck1-cpufreq-230705.patch.gz
cpufreq is a kernel interface to vary the clock rate of the processor -
basically slowing it down to save electrical power. It's of no help with
your problem.
> I have a ts11 version. Will this work?
>
> A noob question: How to have this working? I suppose using the "patch"
> command. I ran "patch -p0 lin.......". By the time I am writing this,
> the command is still running without showing any message.
>
> If this command finishes, what will be the outcome? Having the
> "gettimeofday" working properly?
>
> Can I get cpu ticks or something like that in order to have the real
> microsecond precision?
>
> Regards.
>
>
>
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/ts-7000/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/ts-7000/join
(Yahoo! ID required)
<*> To change settings via email:
<*> To unsubscribe from this group, send an email to:
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
|