5KHz acquisition control

Mon Jun 7 23:45:59 UTC 2010

On 06/07/2010 06:43 PM, Matt Rippa wrote:
> 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.
>
>    
Run ticker with progressively smaller and smaller
ticks until it quits running.  That's too low. :)

If you intend to do some RTEMS operations in the
interrupt, set up an RTEMS Classic timer to do them
and a task to receive them.  If you are adding a context
switch at each ISR, the overhead will go up.
> 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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