[linux-dvb] Re: Is this legal/safe to open a demuxer before opening the frontend ?

[Gerd Knorr <kraxel@bytesex.org>]

Johannes Stezenbach <js@convergence.de> writes:

> It should be legal, but it cannot be made failsafe for some hardware :-(
> 
> (av7110 may crash if you have a frontend which outputs noise when
> not tuned to signal; this is probably a bug in the RTSL or in the
> firmware error handling. Anyway, the host should not crash when the
> av7110 crashes, this is a bug in the av7110 drivers error handling.
> Note that most newer frontends mute their TS output when they cannot
> sync to a signal).

Shouldn't the driver be able to deal with that?  Re-setup the filters
after the arm crashed?  Maybe delay that until the frontend is locked
to avoid the arm crash instantly again?

> To be safe you should 1. tune, 2. wait for FE_GET_EVENT to return
> success, 3. set filters. Before tuning, stop all filters.

I really don't like that.  It's simply impossible to do if frontend
tuning and filtering is done by different applications.

If you want a real-life example for that have a look at the mtt
teletext browser of current xawtv 4.x snapshots.  It doesn't touch the
frontend, it simply opens the demux, sets up some filters and looks
out for teletext streams.  Works fine in parallel to some TV
application running.  If you tune some station on another transponder
with your TV app mtt will notice (because the PAT changes) and adapt
automagically.

  Gerd

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