5KHz acquisition control

[Matt Rippa]

Hi folks -

It sounds like one way forward would be to benchmark my 
performance with a higher resolution system clock. I'm leaning 
towards an external interrupt source because my worry is 
excessive, unnecessary, processor load. With that said it may 
not be an issue with my particular system requirements and may 
in fact be a benefit as Till and Eric suggest. Is there some 
guideline or limit for cranking up the system clock resolution? 
  (System failure being an obvious limit ;)). I'll play around 
and see, but it looks like a safe bet is to have external timers 
available just in case.

My current proposed PC104 board doesn't have an onboard 
interrupt timer. Can anyone suggest one that does? I'd prefer 
this to be onboard. Otherwise I'll go for something on the pci bus.

Thanks again for the input.
-Matt


On 06/07/2010 01:29 PM, Eric Norum wrote:
> Indeed.
> I suspect that many of us expressing concern about kHz and up system
> clock rates are showing our age -- 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.
>
>
> 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
>>> <mailto: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
>>>     <mailto: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 <mailto: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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>>>
>>>
>>>
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>>
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> --
> Eric Norum
> wenorum at lbl.gov <mailto:wenorum at lbl.gov>
>
>
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