[mythtv] Help: trying to trace channel/DVB problem

[Simon Watson]

I'm trying to get to the bottom of a problem I'm experiencing with Myth and my
DVB card. I originally posted the problem here:
http://www.gossamer-threads.com/archive/MythTV_C2/Users_F11/DVB_setup_problem_P67696/

(and have sinced realised that the videodevice field should be "0", although
this doesn't fix my problem)

Essentially, when I run mythbackend, I see:
Starting up as the master server.
trying to change to channel 1

and when I try to watch TV in the frontend, I get "Backend stuffed up in
RequestRingBufferBlock".

Figuring that this might be a symptom of no data from the DVB card, I've now
dusted off my C++ skills and am trying to track down the problem. I'm not sure
if I'm on the right track but the code seems to be returning false from
CheckChannel in DVBChannel::SetChannelByString and not progressing to the
tuning stage.

The query that gets constructed in TVRec::CheckChannel is:
SELECT channel.chanid FROM channel,capturecard,cardinput WHERE channel.channum
= "1" AND channel.sourceid = cardinput.sourceid AND cardinput.inputname = ""
AND cardinput.cardid = capturecard.cardid AND capturecard.cardid = "1" AND
capturecard.hostname = "shuttle";

Running the query with cardinput.inputname = "Television" produces the correct
chanid, but I don't understand the code that sets this query argument. The line
"QString channelinput = chan->GetCurrentInput();" seems fair enough but I don't
understand what

QString ChannelBase::GetCurrentInput(void)
{
    return channelnames[currentcapchannel];
}

is designed to do. What is the channelnames structure designed to contain? Why
would a map of channel names return an input source? And, more importantly, I
can't see how this structure or currentcapchannel gets initialised by the
DVBChannel class. From what I can see, the TVRec object creates a DVBChannel
object in its constructor and immediately calls SetChannelByString.

As you can see, I'm confused! My C++ is rusty and I'm new to Myth, so be gentle
with me but any pointers/solutions would be much appreciated.

Thanks,

Simon.

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