[linux-dvb] Re: High BER's & Glitching with 2.6 kernel, better with 2.4 and 1.0.0-pre2 (Nova-T)

[Johannes Stezenbach <js@convergence.de>]

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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