[linux-dvb] TDA10086 fails? DiSEqC bad? TT S-1401 Horizontal transponder fails

Oliver Endriss o.endriss at gmx.de
Fri Apr 11 23:36:12 CEST 2008


Hartmut Hackmann wrote:
> Hi,
> 
> Oliver Endriss schrieb:
> > Hi,
> > 
> > Manu Abraham wrote:
> >> Oliver Endriss wrote:
> >> ...
> >>> Ok, some calculations according your formula
> >>>
> >>>>>>> BW = (1 + RO) * SR/2 + 5) * 1.3
> >>> 45 MSPS:
> >>> BW = ((1 + 0.35) * 45/2 + 5) * 1.3 = 46
> >>>
> >>> -> cutoff 36 MHz (maximum value supported)
> >>>
> >>> 27 MSPS:
> >>> BW = ((1 + 0.35) * 27/2 + 5) * 1.3 = 30,2
> >>>
> >>> -> cutoff 31 MHz
> >>>
> >>> 22 MSPS:
> >>> BW = ((1 + 0.35) * 22/2 + 5) * 1.3 = 25,8
> >>>
> >>> -> cutoff 26 MHz
> >>>
> >>> Are these calculations correct, or did I miss something here?
> >>
> >> It looks fine, just round it off to the next integer. ie always round it
> >> up, rather than rounding it down. For the cutoff at 36MHz, it is fine as
> >> well, since at the last step, you will not need an offset, since it
> >> would be the last step in the spectrum.
> >> ...
> >>> Afaics a simple pre-calculated lookup table with 32 entries should do
> >>> the job. At least for the cut-off frequency.
> >> That's possible, since you need only 32 precomputed entries, rather than
> >> continuous values. That would be much better too, without any runtime
> >> overheads. Just the table needs to be done nice.
> > 
> > Now I found some time to come back to this issue,
> > 
> > I prepared a small patch to set the cutoff according to Manu's formula.
> > The calculation is simple enough for integer arithmetic, so it is not
> > worth to prepare a lookup-table.
> > 
> > @ldvb:
> > Please test and report whether it works for you.
> > 
> > CU
> > Oliver
> > 
> I intended to do the same.

If I had been aware of that, I would have done something else. ;-)
My time is rather limited these days...

> Since I have a patch for tda10086 which needs public testing as well, i
> would like to propose this:
> I do a static check and integrate the patch in my repository together
> with my patch and ask for public testing.
> Hope this will not overstress the few testers we have ;-)

Ok. Since I don't have the hardware I ran the code with common symbol
rates. The results looked ok.

CU
Oliver

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