[mythtv-users] HDTV digital static with DVB

[Patrick Wagstrom]

> On Tue, 2005-11-08 at 17:14 +1000, ffrr wrote:
> > I chased video glitches from my DVB setup for ages, and with a lot of 
> > help from the list, I finally nailed it.  It was the Si 3112  SATA 
> > controller chip doing nasties on the PCI bus and corrupting the mpeg 
> > stream from the DVB card.
> > 
> > This would correlate with your observation that it is worse with system 
> > load, in particular disk access.
> 
> I have two hard drives.  If I simply cat /dev/dvb/adapter0/dvr0 to a
> file on the SATA drive, I get some glitches.  If I do the same to a file
> on the PATA drive, I get tons of glitches.  If I do it to a ram disk, I
> get a perfect recording.
> 
> So it doesn't look like it's the SATA chipset doing something nasty.  In
> fact, the SATA drive, being on a faster bus, gives me a better recording
> than the PATA drive.  This makes it look more like my original theory of
> being an issue that can be solved in the DVB driver.  Of course, it
> could be the SATA chipset or anything else on the PCI bus, but if
> something were corrupting the DVB traffic, wouldn't it also corrupt
> other traffic, like disk I/O?
> 
> Instead of it being a kernel buffer that is too small, perhaps it is too
> slow to pull the data off of the card?
> 
> --PC

I'm also experiencing the same behavior after a system upgrade from a
low end athlon to a nice new Athlon64.  I just had a chance to do a
little debugging and I found that disabling the SiI chip and all of my
SATA ports did nothing.  Furthermore, for me dumping it to a ram disk
did NOT produce a perfect recording or anything even close to it.  It
was pretty sad indeed.

I also observed the signal levels on the card while I was getting the
stream and I noticed that signal levels dropped noticeable (from f8c4 -
near perfect) to cXXX and bXXX (where XXX varied), causing the signal to
lose out.  This is very interesting and it suggests that the cards are
susceptible to some form of interference related to the bus.  When I
leave the system idle it happily reports a perfect signal all the time.

Here's the hardware that I've got right now that may be relevant:
Athlon 64 3200+, MSI K8N-Neo4 Platinum, pcHDTV HD3000, wintv PVR250, a
bunch of IDE disk drives.

Before when the tuner was in an Athlon 700 with an Epox k7-kxa
motherboard the recordings were crisp and clean.  Maybe it should just
back in there and I need to stream recordings over the network or
something.

I also started a thread on the pchdtv message board about this issue.
You can find it at: http://pchdtv.com/forum/viewtopic.php?p=6378

Unfortunately, I don't think that I'm skilled enough to do this sort of
debugging.  Should we file this bug with pcHDTV or the DVB folks?

--Patrick