Any updates on HRT for the ts-7800?
--- In "charliem_1216" <> wrote:
>
>
> Hi Eric -
>
> --- In "Eric Robishaw" <eric@> wrote:
> >
> > Charlie,
> >
> > Now I'm a little confused.
> > W/o the usleep I can read 20*k*hz easily. I was expecting a
maximum of
>
> Yes, with the CPU in a tight loop.
>
> > 100hz. So as I understand it then, the "10ms for the process to
become
> > runnable again" refers to a system delay that is caused only by
issuing
> > sleep that evidently doesn't occur otherwise...
>
> Here http://marc.info/?l=linux-arm-kernel&m=118789182024254&w=2 is an
> attempt to explain this not-very-intuitive behaviour. Remember that a
> 100 Hz clock (w/o HRT) means the scheduler only wakes runnable threads
> or processes every 10 mS.
>
> >
> > But of-course w/o a sleep, the cpu use goes way up!
> >
> > *Is there any other way you know of to effectively sleep w/o killing
> the cpu
> > and not being impeeded by the timer resolution?*
>
> Well, the options are:
> * increase HZ in the kernel to something more than 100 Hz. Not
> recommended
> * Write your own kernel module to use an available HW timer. Hard for
> mortals, not portable.
> * Use HRT. Highly recommended if available. Portable across most
> platforms & architectures, easy as rebuilding the kernel.
>
> I looked through archived discussions here and unfortunately HRT is
> not available for the TS-7800 kernel. TS-7800 and HRT should be
> available in the next vanilla kernel release, when Alexander
> Clouter's board support patches hit. (They are in 2.6.27rc2 now).
> Orion CPU is now quite well supported in mainline, but it wasn't when
> TS branched their 7800 kernel.
>
> So, sorry, looks like 50 Hz will have to do for now. Perhaps after
> 2.6.27 hits someone can post a step-by-step guide to compiling a
> vanilla kernel with HRT for the TS-7800, and still using the binary TS
> SD card drivers.
>
> Regards, ......... Charlie
>
> >
> > Eric
> >
> >
> > On Fri, Aug 8, 2008 at 7:54 AM, charliem_1216 <charliem_1216@>wrote:
> >
> > > Hi Eric --
> > >
> > >
> > > --- In <ts-7000%40yahoogroups.com>, "Eric
> > > Robishaw" <eric@> wrote:
> > > >
> > > > It doesn't appear to be a sleep issue... as I believe usleep calls
> > > nanosleep
> > >
> > > It shows up as a sleep issue, ...
> > >
> > > > anyhow.
> > > > I just can't read the registers any faster than 50hz (see Jim's
> > > message if
> > > > you haven't already).
> > >
> > > And I have ... The issue is timer resolution. As Jim correctly said,
> > > the timer resolution is 10 mS in normal cases. You asked for a sleep
> > > period of at least 10 mS, so the delay ends up being 10 mS, plus
> > > another 10 mS for the process to become runnable again. Your total
> > > delay is 20 mS, and 1/.02 = 50 Hz.
> > >
> > > The high resolution timers in recent kernels is clean way to solve
> > > this problem, *transparently* giving timers resolution of 1 nS,
> > > without having to write a special kernel driver to use an
available HW
> > > counter. It works great on the other TS boards (ep93xx based), but I
> > > don't know if a) it was available when the TS ts=7800 kernel was
> > > branched, or b) if TS enabled it; hence my suggestion.
> > >
> > > Jim is also right that it is a FAQ, and you can find lots more
> > > discussion about it in the archives and the site I gave you.
> > >
> > > But in any case, good luck with your project!
> > >
> > > Regards, ........ Charlie
> > >
> > > >
> > > > Eric
> > > >
> > > >
> > > >
> > >
> > >
> > >
> >
>
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