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[linux-dvb] Re: High BER's & Glitching with 2.6 kernel, better with 2.4 and 1.0.0-pre2 (Nova-T)
Dave Smith wrote:
>
> Using release 1.0.1 and a 2.4.20 kernel, I have modified the
> tsa5060_set_tv_freq function in the grundig_29504-401 frontend to match
> 1.0.0.-pre2.
>
> Changing the frequency offset from the -pre2 value of 36000000 to the 1.0.1
> value of 36125000 made no apparent difference.
>
> In the -pre2 code, there are no values for cpump or band_select, meaning that
> buf[3] in that function is always set to 0xc0. If I change this to 0x43
> (which I think would be the value when the frequency of the BBC mux from
> Crystal Palace is given) leads to the higher BER rates and many UNConcealed
> errors when tuned to a channel in the BBC mux.
>
> I must admit that my understanding of C is pretty weak, and so I may have
> evaluated the cpump and band_select errors incorrectly. However it does
> appear that the setting of buf[3] (whatever that does) is causing the errors
> on my card.
>
> I hope this helps.
Hm, I had a look at the code and the tsa5060 data sheet.
The band_select stuff is beyond me, as it just sets a few
general purpose output pins. I'm not sure if it does
anything at all, and the only way to find out is to
look at a grundig_29504-401 data sheet or poke around in
the metal box.
The charge pump stuff is also not clear to me. What is
the logic behind that formula?
I would think that either
- the charge pump current depends on the voltage used to drive
the VCO, so: high freq -> low capacitance -> high voltage
at the varactor diode (or is it the other way round?)
-> high cpump
- or one uses a high cpump to change the frequency, and
sets the cpump to a low value afterwards (less noise)
Does anyone know for sure?
Anyway, the current cpump formula look bogus to me:
cpump = freq < 175000000 ? 2 : freq < 390000000 ? 1 :
freq < 470000000 ? 2 : freq < 750000000 ? 1 : 3;
Comments?
Johannes
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