[mythtv] Debugging Unreliable DCT-6200 Recording

Jim Westfall jwestfall at surrealistic.net
Fri Sep 23 15:53:00 UTC 2005

You have mythtv setup using broadcast firewire connection type?

test-mpeg2 -r 1 > blah.ts uses a peer to peer connection type.  Doing this 
seems to initialize something in the driver or dct-6200 and it ends up 
making a boardcast connection work 100% after that.

I know a few people that use the workaround that I do and it works for 
them as well.


jrandall at ftrd.us <jrandall at ftrd.us> wrote [09.23.05]:
> Jim,
> Thanks for the input on this.
> For me, your fix only works for live tv.  I had been doing basically  
> the same thing before, although it's usually faster for me to skip  
> using test-mpeg2 and just go for a few tries with mythfrontend.  The  
> timeout is longer, but I haven't observed any relationship between  
> getting things going correctly with test-mpeg2 and then having them  
> subsequently work in myth.  I am seeing about 50% failure and haven't  
> detected any sort of pattern, although perhaps I will write up a  
> little script and let it go a few hundred trials just to check on that.
> Once livetv starts working, it is true that you are "all set" in the  
> sense that you can (it seems) continue to watch live tv indefinitely,  
> change channels, etc without any problem.  However, if you want to  
> record it is still 50% odds that it works.  Even if you are watching  
> livetv and push the 'r'ecord button, it seems that it resets the  
> connection when switching to record mode and there's a good chance it  
> won't work.
> I suppose another option for a workaround would be to just keep the  
> transport stream open once it is working (just like live tv does when  
> changing channels).  We could look for a way to hand off the open  
> firewire stream to the recording process rather than having it  
> reinitialized every time.
> But that would still require human intervention to get things going  
> in the first place.  I'm going to try to hack up a way for the  
> firewire code to detect when the transport stream connection isn't  
> working and give a few tries at reinitializing it before giving up.
> It looks like libs/libmythtv/firewirerecorder.cpp is the place to do  
> this, so that's where I'm headed.
> I just noticed that there is a bug tracking system, but didn't see a  
> bug for this yet.  Should we add one so we'll have a place to submit  
> the patch?  It'll be good to have others who have this problem to  
> test and make sure it solves it for more than just me.
> Josh.
> On Sep 22, 2005, at 8:16 PM, Jim Westfall wrote:
> >Hi Josh
> >
> >I have this issue as well on one of my dct-6200's.  I havent had time
> >to see what the exact cause it, but the following work around gets it
> >working 100% for me.
> >
> >make sure your firewire connection type is set to broadcast in  
> >mythsetup.
> >
> >run 'test-mpeg2 -r 1 > test.ts' over and over until you get  
> >output.  once
> >you get output stop test-mpeg2 then attempt to watch livetv in  
> >myth.  If
> >livetv works you should be all set.  If not, you will need to  
> >repeat the
> >process until it does.  It will usually take me a few (less then  
> >10) tries
> >to get it in a working state.
> >
> >This process should only be required if you reboot your box or  
> >dct-6200.
> >
> >jim
> >
> >jrandall at ftrd.us <jrandall at ftrd.us> wrote [09.22.05]:
> >
> >>I'm having intermittent trouble recording with my DCT-6200 cable box
> >>connected via firewire.  Basically it seems like about half the time
> >>the program/live tv doesn't start coming in.  For example, when you
> >>select "Watch TV" the screen just goes blank for a little while and
> >>then returns.  If you try a few times, it always starts working
> >>eventually, but it is much more of a problem for recording -- which
> >>fails completely half the time.
> >>
> >>I have seen other people posting similar issues, so I know it is not
> >>just me.
> >>
> >>I suspect that it is not an issue with MythTV per se.  I have also
> >>observed this phenomenon when using the test-mpeg2 utility that comes
> >>with libiec61883.  Basically, running "test-mpeg2 -r 1 > /tmp/foo.ts"
> >>will either start to fill up the file or will leave a 0 byte file
> >>"forever".  Either way, test-mpeg2 says "...Established
> >>Connection..." and "Starting to receive" -- it doesn't seem to know
> >>whether data is actually coming or not.  I also have my DCT-6200
> >>connected directly to a TV for debugging, and I note that it always
> >>glitches a little whenever you start capturing from it (picture
> >>freezes and audio stops for a second, then continues).  This happens
> >>whether the data is transmitted or not.
> >>
> >>When the connection is not working, mythbackend says:
> >>"Firewire: No Input in 15 seconds [P:1 N:1] (select)"
> >>followed by:
> >>"RingBuffer: Couldn't read data from the capture card in 15 seconds.
> >>Stopping."
> >>
> >>Once data starts flowing, I have never observed any problems, but as
> >>I said, it has this problem about 50% of the time.  When using test-
> >>mpeg2 to capture, it isn't really a problem, since I note right away
> >>that no data is flowing and retry until it works.  But, mythtv fails
> >>much harder.  It takes many seconds to timeout on live tv before
> >>letting you retry, and has the problem on channel changing as well.
> >>And recording shows only works about half the time, because it is
> >>either go or no-go... there seems to be no retry possible.
> >>
> >>How should I go about debugging/fixing this?
> >>
> >>We could probably add a way to detect that no data is flowing over
> >>firewire after the receive connection has been established and then
> >>retry the connection, but should this problem be fixed here or at a
> >>lower level (such as in libiec61883?).  Unfortunately, the
> >>linux1394.org server still seems to be down, so I can't check the
> >>buglist there to see if this is a known problem or not.
> >>
> >>It seems probable that the real problem here is with the firmware in
> >>my cable box, but since it is not up to me to update that, I'd rather
> >>see a workaround in software.
> >>
> >>Could someone who is familiar with the firewire STB support in mythtv
> >>let me know where the best place would be to put the fix?  I can
> >>start hacking around, but I'd rather do it "right" the first time.
> >>
> >>Thanks,
> >>
> >>Josh.
> >>
> >>
> >>
> >
> >
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> >>
> >
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