5KHz acquisition control

[Daron Chabot]

On Mon, Jun 7, 2010 at 7:29 PM, Eric Norum <wenorum at lbl.gov> wrote:

> Indeed.
> I suspect that many of us expressing concern about kHz and up system clock
> rates are showing our age --
>

Hey, I resent that notion! I'm no where near as old as you :)

Or is denial just one of the symptoms of getting old ?


>  we used 50 Hz to 100 Hz system clocks back in the days of MVME167 cards
> (25 MHz 68040).   Machines are a lot faster now -- perhaps a 5 kHz clock is
> not unreasonable nowadays.
>

For the record, I also use 1 kHz ticks on our MVME3100 (667 MHz) boards and
on various x86 platforms (from 450 MHz to 3 GHz). No problems.

But, if one can utilize the time-base provided by a sampling ADC, that may
be the right choice to drive this application.

Just a thought.


>
>
> On Jun 7, 2010, at 3:18 PM, Till Straumann wrote:
>
>  Not sure. Having a higher resolution system clock can be quite useful
> since it allows you to use finer-grained timeouts (on semaphores, queues,
> sockets, ...)
> or RTEMS timers etc. which can be desirable.
>
> I have started to use a 1kHz clock by default on our MVME6100 boards
> (1GHz powerpc) without noticeable impact on CPU load.
>
> -- Till
>
>
> On 06/07/2010 05:00 PM, Daron Chabot wrote:
>
> Matt,
>
>  I've used a 455 MHz Pentium 3 interrupting at over 20 kHz as part of a
> VME-based data acquisition system.
>
>  I agree with Robert: if you can generate interrupts at the frequency you
> need, _without_ using system's "ticks", that's the better approach.
> Hopefully your ADC hardware can generate interrupts upon conversion, or upon
> a "high-water-mark", or something similar...
>
>  If that's not an option, you may be able to use one of the spare timers
> on the i8254 chip (if your system is so equipped).
>
>
>  -- dc
>
> On Mon, Jun 7, 2010 at 4:23 PM, Robert Deschambault <
> robert.deschambault at gmail.com> wrote:
>
>> Hi,
>>
>> In my opinion, I wouldn't run the RTEMS with a clock tick like that, I
>> would find a way to generate an external interrupt based on a hardware
>> timer.  I have successfully run RTEMS on a 40 MHz LEON2, with no changes to
>> the RTEMS clock ticks, to accept a 16 KHz interrupt signal for a fuzzy logic
>> control loop to control a gimbal.  Worked very well.
>>
>>
>> On Mon, Jun 7, 2010 at 4:12 PM, Matt Rippa <mrippa at gemini.edu> wrote:
>>
>>> Hi -
>>>
>>> I would like to know your thoughts regarding common practices for an
>>> RTEMS system requiring a 5 KHz sample rate. The hardware is 600MHz
>>> i386/PC-104 based. Reading through the RTEMS C users guide the Rate
>>> Monotonic Scheduler appears to be what I'm interested in. Basically I need
>>> to read inputs from hardware, filter and process results, then write outputs
>>> with a period of 200 us.
>>>
>>> I understand I can set the RTEMS system clock ticks to get this
>>> resolution. My question is, is this a common and recommend practice for this
>>> kind of sample rate? Or do people favor using on-board programmable
>>> interrupt timers for this purpose? Is using an external interrupt timer on
>>> the pci bus a common practice if your SBC doesn't provide any timers?
>>>
>>> Thanks for any input.
>>>
>>> -Matt Rippa
>>> _______________________________________________
>>> rtems-users mailing list
>>> rtems-users at rtems.org
>>> http://www.rtems.org/mailman/listinfo/rtems-users
>>>
>>
>>
>>
>>  --
>> Bob Deschambault
>> 6614 Astro Court, Mississauga
>> Ontario, Canada L5N 7J2
>> home: 905 824 7159
>> cell: 416 457 7163
>>
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>> rtems-users at rtems.org
>> http://www.rtems.org/mailman/listinfo/rtems-users
>>
>>
>
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>
>  --
> Eric Norum
> wenorum at lbl.gov
>
>
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