5KHz acquisition control

[Eric Norum]

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> 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
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>> 
>> 
>> 
>> -- 
>> 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

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