[linux-dvb] Re: Driver problems

[Jussi Alanärä <jalanara@dc.turkuamk.fi>]

On Tue, 3 Feb 2004, Robert Schlabbach wrote:

> "DVB mixer
>
> The VCO can be controlled by an external DC signal to
> provide a carrier for the down-conversion of the DVB-IF
> signal. The VCO frequency as a function of the voltage at
> pin 16 is given in Figs 10 and 11."
>
> In the end, this makes the PWM value an _AFC_ value. You can find the
> optimum value by checking the VES1820 VAFC register - if it reads a
> negative value, increase the PWM value, if it reads a positive value,
> decrease the PWM value - until you get VAFC as close to 0 as possible.

Is it that simple? I assume VAFC is same as AFC reported by ves1820 with
verbose=1. And all this is with QAM128 channels, which seems to have
something to do with all these problems here. Can't test QAM64 channels
anymore.

Now I adjusted PWM to 0x53 (eeprom value is 0x52) so that I get: DVB:
VES1820(1): AFC (0) 0Hz

and then tune to 146MHz and start monitoring:

video:~# dvbtune -c 1 -f 146000000 -qam128 -I0 -m
Signal=65535, Verror=142970, SNR=59881dB, BlockErrors=-1, (S|L|C|V|SY|)
Signal=65535, Verror=139460, SNR=59367dB, BlockErrors=6, (S|L|C|V|SY|)
Signal=65535, Verror=139460, SNR=58853dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=135590, SNR=59881dB, BlockErrors=5, (S|L|C|V|SY|)
Signal=65535, Verror=135590, SNR=59110dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=138920, SNR=59624dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=138920, SNR=59881dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=135730, SNR=59367dB, BlockErrors=1, (S|L|C|V|SY|)
Signal=65535, Verror=135730, SNR=59881dB, BlockErrors=3, (S|L|C|V|SY|)
Signal=65535, Verror=131630, SNR=59624dB, BlockErrors=0, (S|L|C|V|SY|)

As you can see, Verror rate is HIGH and BlockErrors start to appear.

Then when tuning to some higher frequencies, 410MHz for example:

video:~# dvbtune -c 1 -f 410000000 -qam128 -I0 -m
Signal=65535, Verror=4110, SNR=60395dB, BlockErrors=-1, (S|L|C|V|SY|)
Signal=65535, Verror=4110, SNR=61166dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=4230, SNR=60652dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=4230, SNR=60909dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=3950, SNR=60652dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=3950, SNR=60138dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=4030, SNR=60652dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=4030, SNR=60909dB, BlockErrors=0, (S|L|C|V|SY|)

Verror rate is reasonable and no BlockErrors.

Then I'll change the PWM to much higher, which i've been using for couple
of months and that's PWM=0x64 giving me: DVB: VES1820(1): AFC (29) -195410Hz

and also monitoring the signal the Verror rate is down even in 146MHz

video:~# dvbtune -c 1 -f 146000000 -qam128 -I0 -m
Signal=65535, Verror=8630, SNR=61423dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=8630, SNR=60652dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=7690, SNR=60395dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=7690, SNR=60652dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=9320, SNR=60909dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=9320, SNR=60138dB, BlockErrors=0, (S|L|C|V|SY|)

and with the same PWM in 410MHz:

video:~# dvbtune -c 1 -f 410000000 -qam128 -I0 -m
Signal=65535, Verror=690, SNR=61680dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=690, SNR=61166dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=690, SNR=61937dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=740, SNR=61937dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=740, SNR=61937dB, BlockErrors=0, (S|L|C|V|SY|)
Signal=65535, Verror=680, SNR=61680dB, BlockErrors=0, (S|L|C|V|SY|)

PWM I'm using at the moment is a compromise between Verror rate and tuning
speed. Optimal value for small Verror rate is PWM=0x66 but then channel
changes are too slow. But with PWM=0x64 time to tune is reasonable.


/Jussi


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