[linux-dvb] Re: Budget DVB-C tuning problems

[Johannes Stezenbach <js@convergence.de>]

Robert Schlabbach wrote:
> 
> When developing my Windows VES1820 driver, I found the following: The
> VES1820 AFC logic is a bit flawed and can get "stuck" at a high off-center
> value. At this stage, you have to reset the VES1820 (set register 0 bit 0
> to 0 then to 1) to reset the AFC, which will make the VES1820 lock.
> 
> I found a way to both optimize the channel changing times and to make
> channel changes reliable at the same time: When only the tuning frequency
> has changed (i.e. the demodulator settings are unchanged), do _NOT_
> immediately reset the demodulator. Instead, wait 10 milliseconds and then
> read the VAFC register. If it is outside the range [-4 ... +4], reset the
> demodulator.
> 
> This way, channel changes will typically occur in less than 10 ms (if no
> reset was necessary), and if the AFC gets stuck, it will lock in typically
> less than 50ms (after a reset, the VES1820 needs at least 35ms to lock).
> 
> If you're up to it, try implementing this in the Linux driver. It is
> working very well in my Windows driver.

Hmm, that sounds interesting. Thanks a lot for the information.

I think the delay bug in the frontend thread might have caused the
problems (see "Slow Channel Switch with latest CVS (again)"), but
with your input the ves1820 driver could be improved.
Does someone have time to work on it?

Too bad you're not a Linux guy :-(

Johannes


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