[linux-dvb] DVB-C driver (Re: More thoughts on coldboot driver crash)

[Jaakko Hyvätti <jaakko@hyvatti.iki.fi>]

  I believe there are two problems:

1.  The IF frequency in ves1820.c:tuner_set_tv_freq() is wrong, the
correct value I suspect is 36.000MHz.  It used to be 36.125MHz up to
-r1.7.  Back then there was a -0.125MHz frequency offset needed when
tuning QAM64 channels on Helsinki cable.  In revision 1.8 it was changed
to 36.250MHz, after which there has been a -0.250MHz freq offset needed.
Also some random documents from web which describe interfacing with the
Mitel SP5659 (found on Hauppage DVB-C) mention 36.000MHz frequency.

With this the QAM64 stream is solid.  I have been reading the AFC register
of ves1820, and it stays within about 0.02MHz.

Are there networks, cards, tuners or combinations of them anywhere in the
world where the IF frequency must be something other than 36.000MHz?

2.  QAM128 settings are wrong.  I know they are according to the
datasheet, checked myself, but something seems wrong with Hauppage DVB-C
at least.  The strongest evidence is I think the AFC register, which jumps
back and forth +-0.7MHz !!  I'll investigate further later when this flu
releases me from its grib and I have some free time.

  I would guess if these problems are fixed, the zigzag may be disabled
for DVB-C.  Maybe even bending can go, afc moves the tuner back to the
exact freq anyway.  Maybe it can stay as a bending step of 0.06MHz is no
problem for AFC to correct.

  Btw it would be nice to have the ves1820 frontend store the freq it was
tuned to so that ..GET_FRONTED could be implemented to return the true AFC
corrected freq.  Isn't this how it is meant to work?  I'll make a patch
some day to implement this.

Jaakko

-- 
Foreca Ltd                                           Jaakko.Hyvatti@foreca.com
Pursimiehenkatu 29-31 B, FIN-00150 Helsinki, Finland     http://www.foreca.com


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