<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Indeed.<div>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.</div><div><br></div><div><br><div><div>On Jun 7, 2010, at 3:18 PM, Till Straumann wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
<div bgcolor="#ffffff" text="#000000">
Not sure. Having a higher resolution system clock can be quite useful<br>
since it allows you to use finer-grained timeouts (on semaphores,
queues, sockets, ...)<br>
or RTEMS timers etc. which can be desirable.<br>
<br>
I have started to use a 1kHz clock by default on our MVME6100 boards<br>
(1GHz powerpc) without noticeable impact on CPU load.<br>
<br>
-- Till<br>
<br>
<br>
On 06/07/2010 05:00 PM, Daron Chabot wrote:
<blockquote cite="mid:AANLkTimcRH8L6MOphHibx6kmJ5YXiJAAhmF9eetYnIwX@mail.gmail.com" type="cite">Matt,
<div><br>
</div>
<div>I've used a 455 MHz Pentium 3 interrupting at over 20 kHz as
part of a VME-based data acquisition system.</div>
<div><br>
</div>
<div>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...</div>
<div><br>
</div>
<div>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).</div>
<div><br>
</div>
<div><br>
</div>
<div>-- dc<br>
<br>
<div class="gmail_quote">On Mon, Jun 7, 2010 at 4:23 PM, Robert
Deschambault <span dir="ltr"><<a moz-do-not-send="true" href="mailto:robert.deschambault@gmail.com">robert.deschambault@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi,<br>
<br>
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.
<div>
<div class="h5"><br>
<br>
<div class="gmail_quote">On Mon, Jun 7, 2010 at 4:12 PM, Matt Rippa
<span dir="ltr"><<a moz-do-not-send="true" href="mailto:mrippa@gemini.edu" target="_blank">mrippa@gemini.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hi
-<br>
<br>
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.<br>
<br>
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?<br>
<br>
Thanks for any input.<br>
<font color="#888888"><br>
-Matt Rippa<br>
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<font color="#888888">-- <br>
Bob Deschambault<br>
6614 Astro Court, Mississauga<br>
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home: 905 824 7159<br>
cell: 416 457 7163<br>
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