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

[Peter Bieringer <pb@bieringer.de>]

--On Saturday, August 16, 2003 05:46:02 PM +0200 Robert Schlabbach
<robert_s@gmx.net> wrote:

>> 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.

Interesting...

> 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

Can be done easily by changing "if 0" -> "if 1" on top of 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.

First card: pwm=52
f 354000000:
ves1820.c: AFC (32) -215625Hz

f 362000000:
ves1820.c: AFC (32) -215625Hz

f 370000000:
ves1820.c: AFC (32) -215625Hz

f 394000000:
ves1820.c: AFC (-33) 222364Hz

f 410000000:
ves1820.c: AFC (32) -215625Hz

f 426000000:
ves1820.c: AFC (-33) 222364Hz


Second card: pwm=48
f 354000000:
ves1820.c: AFC (1) -6738Hz

f 362000000:
ves1820.c: AFC (1) -6738Hz

f 370000000:
ves1820.c: AFC (1) -6738Hz

f 394000000:
ves1820.c: AFC (-2) 13477Hz

f 410000000:
ves1820.c: AFC (1) -6738Hz

f 426000000:
ves1820.c: AFC (-2) 13477Hz


Are these jumps in AFC depending on frequency normal? Is my first card
buggy?


> 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.

Hmm, in which direction? And how per card?

Will wait for further tests now in which direction I should change pwm

> 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? :)

They are fast enough I think, not an issue here.

        Peter
-- 
Dr. Peter Bieringer                     http://www.bieringer.de/pb/
GPG/PGP Key 0x958F422D               mailto: pb at bieringer dot de 
Deep Space 6 Co-Founder and Core Member  http://www.deepspace6.net/


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