[mythtv-users] Problem with a second DVB card, help needed

Henry A Harper III hah at alumni.rice.edu
Fri Sep 22 20:57:56 UTC 2006

> I have a following DVB cards related problem and I'm not sure if it's
> related to Myth or DVB drivers / kernel.
> I've used one Technisat Airstar 2 DVB-T card succesfully with Myth for
> many months. Now I'm trying to get two of these cards to work at the
> same time (FC5, 2.6.17-1.2187_FC5smp) but haven't succeeded yet.
> With all the other apps (dvbscan, dvbstream, kaffeine, mplayer) I can
> successfully tune to channels, and watch programs with both cards. With
> mplayer I can succesfully watch two different programs from separate
> cards at the same time.
> Problem is that when I try to use these two cards *at the same time*
> with Myth, the second card is not working. First card records program
> fine but although Myth starts to record a program, the recording is
> never made with the second card (the file does not exist).
> And more strangely, after this kind of failure, if I stop the backend
> I'm not anymore able to use any other apps with the failed card. Tuning
> doesn't work etc. After reboot everything is okay again. How is this
> possible? Could apps using DVB API misuse the card somehow so that it is
> leaved to non-working state? Or does this clearly show that this is
> kernel / driver issue?
> Both cards work separately with Myth. I can record a show with card 1,
> stop backend, update card priority so that second card gets higher
> priority, start backend again and successfully record a show with the
> second card.
> The problem is simultaneous usage of cards. I know that there are lots
> and lots of people using multiple DVB cards without problems. And it
> feels like driver / kernel  issue.. but how is mplayer able to use both
> cards then and myth not?
> Any ideas what is going on or how to troubleshoot this further?

What are your logfiles (mythbackend particularly) showing?  Is there an
error message when the second card tries to start a recording? What size is
your ringbuffer setting? What does /proc/meminfo show for free/used vmalloc
space? I have just been through something similar (perhaps - I didn't notice
that particular backend lockup) with 3 DVB cards, the 3rd one wouldn't work
at the same time as the other two. All three are able to record
simultaneously now though, with a larger vmalloc kernel parameter.


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