Mailing List Archive: MythTV: Dev

Backend crash on tuning to any DVB channel

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daniel at 34SP

Mar 17, 2006, 8:33 AM

Post #1 of 5 (1068 views)
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Backend crash on tuning to any DVB channel

I'm seeing a problem since updating past revision 9305 with tuning to
any channel on DVB causing mythbackend to crash. This is showing up
either with tuning to record/watch TV or with the BE tuning to do EIT
scanning.

This problem is not present in revision 9300 but is in 9310 and later,
the following is tested today using 9398.

Attached is the information mentioned in 22.2 of the HOWTO, a backtrace
and the myth.log from starting up the backend to it crashing shortly
afterwards.

--
Daniel Foster
Technical Director
34SP.com

Attachments:

myth.log.gz (1.81 KB)

gdb.txt.gz (3.22 KB)

mocm at mocm

Mar 17, 2006, 9:10 AM

Post #2 of 5 (989 views)
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Backend crash on tuning to any DVB channel [In reply to]

>>>>> "Daniel" == Daniel Foster <daniel[at]34SP.com> writes:

Daniel> I'm seeing a problem since updating past revision 9305
Daniel> with tuning to any channel on DVB causing mythbackend to
Daniel> crash. This is showing up either with tuning to
Daniel> record/watch TV or with the BE tuning to do EIT scanning.

Daniel> This problem is not present in revision 9300 but is in
Daniel> 9310 and later, the following is tested today using 9398.

Daniel> Attached is the information mentioned in 22.2 of the
Daniel> HOWTO, a backtrace and the myth.log from starting up the
Daniel> backend to it crashing shortly afterwards.

I don't know if this is related, but I always get a segfault, when the
backend tries to read the EIT. I trakced it back to the CalcCRC call
in pespacket.c. Apparently the ProgramAssociationTable class inherits
the PesPacket class vioa the PSIPTable class and CalcCRC crashes when
it wants to calculate the Length() of the PesPacket. I haven't traced
it all through. I guess the reason is that the Finalize call is made
without checking if there even is a CRC. I am also not sure if
treating a TS section as PES is the right choice, but I haven't worked
through all the classes, so I can't really comment on that.

Marcus

--
/--------------------------------------------------------------------\
| Dr. Marcus O.C. Metzler | |
| mocm[at]metzlerbros.de | http://www.metzlerbros.de/ |
\--------------------------------------------------------------------/
|>>> Quis custodiet ipsos custodes <<<|
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danielk at cuymedia

Mar 18, 2006, 8:53 AM

Post #3 of 5 (988 views)
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Re: Backend crash on tuning to any DVB channel [In reply to]

On Fri, 2006-03-17 at 16:33 +0000, Daniel Foster wrote:
> I'm seeing a problem since updating past revision 9305 with tuning to
> any channel on DVB causing mythbackend to crash. This is showing up
> either with tuning to record/watch TV or with the BE tuning to do EIT
> scanning.
>
> This problem is not present in revision 9300 but is in 9310 and later,
> the following is tested today using 9398.
>
> Attached is the information mentioned in 22.2 of the HOWTO, a backtrace
> and the myth.log from starting up the backend to it crashing shortly
> afterwards.

Can you try the latest SVN, and create a ticket if the problem is
still present there? We just did a ffmpeg resync which broke the
CRC functions, but it should be fixed now.

-- Daniel

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danielk at cuymedia

Mar 18, 2006, 9:12 AM

Post #4 of 5 (974 views)
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Re: Backend crash on tuning to any DVB channel [In reply to]

On Fri, 2006-03-17 at 18:10 +0100, Marcus Metzler wrote:
> I don't know if this is related, but I always get a segfault, when the
> backend tries to read the EIT. I trakced it back to the CalcCRC call
> in pespacket.c. Apparently the ProgramAssociationTable class inherits
> the PesPacket class vioa the PSIPTable class and CalcCRC crashes when
> it wants to calculate the Length() of the PesPacket. I haven't traced
> it all through. I guess the reason is that the Finalize call is made
> without checking if there even is a CRC.
Marcus this sounds like a different problem, Daniel Foster's problem
was/is due to a recent SVN resync.

The Finalize() call should only be called on PES packets we construct,
which should always have a CRC. The VerifyCRC() call is called on
packets we read in, but should just return true if there is no CRC.

> I am also not sure if
> treating a TS section as PES is the right choice, but I haven't worked
> through all the classes, so I can't really comment on that.
AddTSPacket was supposed to be a temporary hack until Taylor Jacob
got the pes packet constructor he was using working correctly. But
since he hasn't had time for MythTV coding in a while, so a proper
pes packet assembler is now on my TODO. At the time he had copies
of the MPEG specs, while my AddTSPacket was just reverse engineered
in 20 minutes from the streams I had. I now have a copy of the
important bits of the MPEG-2 spec, but haven't had a chance to look
at it yet.

-- Daniel

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daniel at 34SP

Mar 20, 2006, 2:14 AM

Post #5 of 5 (961 views)
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Re: Backend crash on tuning to any DVB channel [In reply to]

Hi Daniel,

> Can you try the latest SVN, and create a ticket if the problem is
> still present there? We just did a ffmpeg resync which broke the
> CRC functions, but it should be fixed now.

Seems to be fine - the BE is happily running SVN 9410 and tuning and EIT
scanning now. I can't check anything else until I get home later on but
thanks for that one at least :-)

--
Daniel Foster
Technical Director
34SP.com
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