Jan Kiszka wrote:
Gilles Chanteperdrix wrote:
On Fri, Apr 4, 2008 at 12:45 PM, Jan Kiszka <[EMAIL PROTECTED]> wrote:
Sebastian Smolorz wrote:

Jan Kiszka wrote:

Sebastian Smolorz wrote:

Jan Kiszka wrote:

This patch may do the trick: it uses the inverted tsc-to-ns function
instead of the frequency-based one. Be warned, it is totally untested inside
Xenomai, I just ran it in a user space test program. But it may give an
Your patch needed two minor corrections (ns instead of ts in functions
xnarch_ns_to_tsc()) in order to compile. A short run (30 minutes) of latency
-t1 seems to prove your bug-fix: There seems to be no drift.
That's good to hear.

If I got your patch correctly, it doesn't make xnarch_tsc_to_ns more
precise but introduces a new function xnarch_ns_to_tsc() which is also less
precise than the generic xnarch_ns_to_tsc(), right?
Yes. It is now precisely the inverse imprecision, so to say. :)

So isn't there still the danger of getting wrong values when calling
xnarch_tsc_to_ns()  not in combination with xnarch_ns_to_tsc()?
Only if the user decides to implement his own conversion. Xenomai with
all its skins and both in kernel and user space should always run through
the xnarch_* path.
OK, would you commit the patch?

 Will do unless someone else has concerns. Gilles, Philippe? ARM and
Blackfin then need to be fixed similarly, full patch attached.

Well, I am sorry, but I do not like this solution;
- the aim of scaled math is to avoid divisions, and with this patch we
end up using divisions;

Please check again, no new division due to my patch, just different parameters for the existing one.

- with scaled math we do wrong calculations, and making a wrong
xnarch_ns_to_tsc only works for values which should be passed to

IMHO, the error is within the range of the clock's precision, if not even below. So struggling for mathematically precise conversion of imprecise physical values makes no sense to me. Therefore I once proposed the scaled-math optimization.

But this does not mean that I'm opposing even faster division-less ns_to_tsc with scaled-math parameters, i.e. combining best of both worlds!


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