Re: [Xenomai-help] Xenomai 2.5-rc2 clock_gettime bad tv_nsec value

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Steve wrote:
> 2009/8/20 Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org
> <mailto:gilles.chanteperdrix@xenomai.org>>
> 
>     Steve wrote:
>     > On 19/08/2009, Gilles Chanteperdrix
>     <gilles.chanteperdrix@xenomai.org
>     <mailto:gilles.chanteperdrix@xenomai.org>> wrote:
>     >> Steve wrote:
>     >>> Were you going to delay handling this until later, or were you
>     hoping
>     >>> it wouldn't be a problem?  If it's the former then this is not my
>     >>> number one priority at the moment, so from my perspective I can wait
>     >>> until the next release candidate / release.
>     >> To be completely frank, I was not really worried about this
>     issue, since
>     >> you had not answered, I thought that maybe the issue was in your test
>     >> program.
>     >>
>     >>> Linux kernel: 2.6.29.4
>     >>> Xenomai: 2.5-rc2
>     >>> Adeos: adeos-ipipe-2.6.29.4-x86-2.4-01
>     >>>
>     >>> OS: Ubuntu (8.04 with updates)
>     >>> Hardware:
>     >>> Intel Core 2 CPU, kernel compiled using processor family
>     'Pentium-4/etc'
>     >> compiled for 32 or 64 bits?
>     >>
>     >> --
>     >>                                           Gilles
>     >>
>     >>
>     >
>     > 32 bit,
> 
>     Ok. It turns out that the error is portable, and there is no other way
>     than to fix the result after the multiplication (trying to round
>     differently leads to the converse error). So, could you try the
>     following patch:
> 
>     diff --git a/include/asm-generic/bits/timeconv.h
>     b/include/asm-generic/bits/time
>     index 79060b3..aa595fe 100644
>     --- a/include/asm-generic/bits/timeconv.h
>     +++ b/include/asm-generic/bits/timeconv.h
>     @@ -60,10 +60,17 @@ long long xnarch_ns_to_tsc(long long ns)
>      unsigned long long xnarch_divrem_billion(unsigned long long value,
>                                             unsigned long *rem)
>      {
>     -       unsigned long long r;
>     -       r = xnarch_nodiv_ullimd(value, bln_frac.frac, bln_frac.integ);
>     -       *rem = value - r * 1000000000;
>     -       return r;
>     +       unsigned long long q;
>     +       unsigned r;
>     +
>     +       q = xnarch_nodiv_ullimd(value, bln_frac.frac, bln_frac.integ);
>     +       r = value - q * 1000000000;
>     +       if (r >= 1000000000) {
>     +               ++q;
>     +               r -= 1000000000;
>     +       }
>     +       *rem = r;
>     +       return q;
>      }
>      #else /* !XNARCH_HAVE_NODIV_LLIMD */
>      long long xnarch_ns_to_tsc(long long ns)
> 
> 
>     --
>                                                Gilles.
> 
> Hi,
> 
> I have applied the patch and it works - the kernel messages from the
> previous patch are no longer produced, and my test program works without
> clock_gettime tv_nsec checks.  Thank you.
> 
> Just for completeness, are we sure that the value given by r is never
> more than 2 billion?  I only ask because the patch only deals with one
> second worth of overrun.

Yes. The multiplication used to compute q may only be off by one.

-- 
                                          Gilles