[mythtv-users] recommend PCI DVB-T Tuner Card?

Ed W lists at wildgooses.com
Thu May 13 18:18:09 UTC 2010


> Do you have any other devices plugged into the USB (for example, a USB
> hard drive).  It's possible there is bus contention which results in
> packet loss.

Yes I have a USB keyboard plugged in so I guess it's possible, but the 
keyboard has been there for years and I'm not sure what tools there are 
in linux to check for such contention.  I will briefly unplug it to 
check though

> Which tuner product is it?  Knowing what product will tell us what
> chips it contains, which might offer some insight.

It's the afatech 9013 which uses the afatech_9015 linux driver.  I 
actually replied to the thread where I posted some dmesg results 
previously, but I think the chipset alone probably defines it's problems?
> Also, do you *ever* see the SNR/BER count change?

Actually yes, if I flick to certain muxes then I see non zero BER and 
the occasional UNC increase which corresponds with a visual gremlin.  
However, I am seeing additional breakup which is NOT correlated with UNC 
increasing and additionally it occurs on other channels which aren't 
showing anything other than zero BER count...

Having investigated further I'm wondering if it might be a bug in trunk 
which I also updated when I swapped the hardware.  The symptoms are that 
the glitches only occur after recording for a few minutes.  If I 
literally simply retune to the same channel then the glitches disappear 
for another few mins.  Feels like perhaps a bug in the recording code, 
but I can't see anything interesting in the commit logs?

> You may also which to run top when you are seeing the problem, and
> make sure there is not some batch job coming around during recording
> which is starving the CPU.

Sure - used top and also checked for other similar issues.  Actually I 
can run a "make -j4" in the background and it doesn't change the basic 
params of the several mins before glitches start.  Also hdparm gives 
sensible write speeds.

I have only just thought about using tzap and mplayer to compare, but 
will test this next...

> It's possible there is a bug in the tuner driver which causes the
> tuning to drift over time.  Are you sure this exact tuner product
> works correctly in your old system?

I have a several days of recordings using the same card on my old atom 
system, so yes I believe the same card has worked previously.  However, 
I now have three similar cards and I have now mixed them up - very 
possibly I have a duff card and certainly a tuning drift might also 
explain this...

I will test with tzap and mplayer

Thanks for any notes on other ways to test the output of the card is 
perfect or not and where the glitches could be being introduced?


Ed W

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