[mythtv] DVB, HD-2000, and CRCs

Taylor Jacob rtjacob at earthlink.net
Mon Mar 21 14:07:19 UTC 2005


Quoting Doug Larrick <doug at ties.org>:

<snip>

> Then explain to me how I'm seeing log entries like this:
> Title [4001][003B] = Lixe With Rewis and Kel,y\uffff\uffff         Mon
> Mar 21 09:00:00 2005 - Mon Mar 21 10:00:00 2005

Probbably the errors are slipping past CRC32.. There isn't any validation on the
ATSC tables like there is for the DVB ones in my code yet.. If the guide on
those shows is huffman compressed then its even more likely you will get worse
results by 1 bit being off.. I need to write some more robust table validation
(checking for all the possible fixed bits in the tables before processing them)
since these can get through from time to time..  I was actually thinking about
that earlier today.. I have had my backend segv a few times on bad channels
becasue of getting lost processing MGTs..

> Is this likely to be a bug in the driver?

No.  You see this all the time. CRC32 isn't very robust.. You will see PATs
screwed up more often than not if you have a bad signal.. I rarely see problems
like this with DVB, which I suspect is just due to the low quality of the
demodulators used on any of the cards here in comparison to the rest of the
world..

> I'm also seeing "MSS WITH MORE THAN 1 SEGMENT" messages; I'll see if I
> can do something about that.

Thats just a matter of concating the multiple strings together.. Shouldn't be
too hard to fix, at the time I think i was more interested in just getting
something working..

Taylor


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