[linux-dvb] Re: DVB-C tuning problems caused by inittab changes in ves1820.c since 2003-05-24

["Robert Schlabbach" <robert_s@gmx.net>]

From: "Peter Bieringer" <pb@bieringer.de>
> Both not working, but following is working:
>
> CLKCONF = 0x12

Good, as this is the default value from the data sheet.

> CARCONF = 0x52

BAD, as this is the bit responsible for most VES1820 locking problems. From
the documentation on this bit:

"CAR_P[2] CAR_P[2] determines whether the carrier acquisition range is ±
2.5% of
the Symbol Rate (CAR_P[2]=0) or ± 8% (CAR_P[2]=1). Default is

CAR_P[2]=0."

So this bit really should not be needed. Your problem may actually be a
different one:

> I'm not sure about your comment that frequencies in cable systems are
> usually correct. Earlier versions display AFC information somewhere
> and I saw a not very small difference.

Aha! Your card may be mis-tuned. The Siemens cards have a TDA9819 IF
amplifier on them, with a VCO-controlled output frequency. That frequency
is modified by using the infamous "PWM" output, which is supposedly
measured INDIVIDUALLY for each card after manufacturing and then written to
the EEPROM on the card.

The PWM value for your card may be incorrect, or maybe your card's
characteristics changed due to aging.

As to why you are no longer seeing the AFC displayed, the CVS comment says:

- printk() -> dprintk() for AFC in ves1820.c

So you could just change it back to get the AFC displayed again (or somehow
enable dprintk output...)

Then take a look at read_pwm() in VES1820.C. Also enable the dprintk output
there (e.g. by changing it to printk as well). What PWM value is displayed?
If it's 0xFF, your EEPROM is damaged.

Either way, try inserting a line to override the PWM value and try a few
values and see if you can minimize the AFC output. What optimum value do
you come up with?

After you have found an optimal PWM value, try changing the CARCONF
register back to 0x12 again. Does it work now?

If it does, a way to fix/override the PWM value should be added. After all,
even if it can be "fixed" by extending the carrier acquisition range, this
would still lead to longer channel lock-in times than properly tuning the
board. And you'd want to minimize the channel change times, wouldn't you?
:)

Regards,
--
Robert Schlabbach
e-mail: robert_s@gmx.net
Berlin, Germany



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