[linux-dvb] TDA10086 fails? DiSEqC bad? TT S-1401 Horizontal transponder fails
hartmut.hackmann at t-online.de
Fri Apr 11 23:12:18 CEST 2008
Oliver Endriss schrieb:
> 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.
> Please test and report whether it works for you.
I intended to do the same.
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 ;-)
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