[linux-dvb] Re: Tuning with driver 2001-05-28

[Johannes Stezenbach <js@convergence.de>]

Klaus Schmidinger wrote:
> 
> I have been running a lot of tuning tests and found that there is
> one channel that most of the time doesn't get tuned to correctly:
> 
> CNN:12168:v:0:27500:165:100:0:0:28512
> 
> (that's in VDR's channels.conf notation).
> 
> According to the latest issue of Infosat's channel listing these
> values should be ok (and sometimes it does tune correctly).

I don't have any problems tuning to CNN.


> Could there be a problem in the tuning mechanism of the driver?
> When trying to tune to this channel I sometimes get the error code
> for "Device or resource busy" whe trying to set the PIDs.

Well, there is a catch associated with setting the PIDs:
Assuming channel A has video/audio PIDs 100/101, and channel
B has PIDs 101/102 (on a different transponder, obviously).
Then when switching from A to B you will get "device or resource
busy" when trying to set the video PID because the old audio PID
is still active (the demux hardware allows only one PES filter per PID).

If the driver is loaded with pids_off=0 (default in the Makefile
from the CVS distribution), DMX_STOP and/or closing the demux file
descriptor will *not* free the hardware filter.
(pids_off=0 is meant to be used with tuxzap/tuxview, so you can
continue to watch with tuxview after you have quit tuxzap.)

OTOH, when you try to set a PID filter and it fails, the hardware
filter formerly associated with this demux file descriptor will be freed.

Solution: If one of the DMX_SET_PES_FILTER ioctls returned EBUSY,
retry them all (i.e. set A/V/TT, and when one failed, set A/V/TT again).
If you have set a teletext PID for some channel, and then tune to a
channel w/o teletext PID, reset the teletext PID to 0x1fff (which will
generate an error, but the hardware filter will be freed).
If you tune to a radio channel, be shure to reset the video PID to
0x1fff, too.


> Once a channel hasn't been tuned to correctly, other channels also
> start failing. This is probably the reason why it runs so unstable
> on my system, because I have three DVB cards, two of which are
> permanently switching channels to scan for EPG data.

I haven't checked it with multiple DVB cards, but with a single
card it works quite reliably here.


HTH,
Johannes


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