Re: [microblaze-uclinux] 10 msec number of ticks bug..

["DeviPrasad Natesan" <ndprasad@xxxxxxxxx>]

John,
I rechecked the microblaze timer document, it does say it correctly
(matches whatever i calculated). So the code should have been

count = ((unsigned)-1) - CONFIG_XILINX_CPU_CLOCK_FREQ / rate + 2;

instead of "count = ((unsigned)-1) - CONFIG_XILINX_CPU_CLOCK_FREQ / rate - 2;"

I also retested in our board with a free running clock. So please
apply the change.

Also, please correct the following in the do_settimeofday() in the
time.c. The "#if 0" should be removed. Otherwise, it wouldn't count
the elapsed ticks whenever settimeofday() called potentially leading
to the fixed offset.

#if 0
       tv->tv_usec -= mach_gettimeoffset ();
#endif


Thanx
- Prasad
On 6/4/06, John Williams <jwilliams@xxxxxxxxxxxxxx> wrote:
> Hi Prasad,
>
> DeviPrasad Natesan wrote:
>
> > I had 10msec accuracy problem in my system (ntpd had many drift). Then
> > i could figure out 300 ticks drift happening every second becos of the
> > wrong initial value in the timer register i belive. We verified my
> > change with the free running counter implemented in the fpga and
> > comparing the value every one second and we could see a drift of
> > around 6 ucsec.
> >
> > The change is in the microblaze_timer.c
> >
> > From
> >      count = ((unsigned)-1) - CONFIG_XILINX_CPU_CLOCK_FREQ / rate - 2;
> >
> > to
> >       count = -(CONFIG_XILINX_CPU_CLOCK_FREQ / rate) + 1;
> >
> > One extra tick is required (might be bcos of an extra tick happening
> > while loading the value back to the comparator register.
>
> Interesting - it's a long time since I looked at that code, but from memory I
> did the timer counter load value based on the formula in the opb_timer
> datasheet.  As you say, perhaps it's necessary to compensate for the time it
> takes to actually reset the counter?
>
> > Please confirm this and if it is right apply the change.
>
> You say you tested with with ntpd / ntpclient?  Can you please post a few
> details about your test, and I'll try to replicate it here.
>
> Thanks for your efforts,
>
> John
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