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

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

On Thu, 2 Jan 2003, Jaakko Hyvätti wrote:
> 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.

Testing further.. These AFC values I recorded when IF was 36.000MHz:

tuning     AFC
MHz        MHz
161.875    +0.0483
161.937    -0.0138
162.000    -0.0828
162.125    -0.2070

The average of the tuning+AFC frequencies is 161.92 MHz in the above
example.  This would mean that the closest IF that would work with AFC
closest to zero would be 35.9375 MHz.

> 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 must retract this statement.. now I got good afc values from QAM128
streams too.  The same IF = 35.9375 MHz seems to hold here too, all
frequencies from 138MHz carrier up to 297MHz carrier in Helsinki cable
network.  I have new patch at http://www.iki.fi/hyvatti/dvb/ with these
tweaks.

  Anyway, the most important thing is that zigzag is disabled.  The tuning
takes 1-2 seconds in worst case.  I guess it is the slow afc, maybe it
takes time to settle.  Are there any parameters to make that a bit faster?
Charge pump currents or such?

Jaakko

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


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