[linux-dvb] Re: It works!

[Marcus Metzler <mocm@metzlerbros.de>]

Johannes Stezenbach writes:
 > Holger Waechtler wrote:
 > > Brad Campbell wrote:
 > > >
 > > >I thought the easy way to do it would be to add a second
 > > >dvb_dmx_swfilter() designed around 204 byte packets..
 > > >I can't see an *easy* and reliable way to autodetect the incoming 
 > > >stream, particularly one that is not succeptible to trying to switch 
 > > >formats when a corrupt packet is recieved.
 > > 
 > > It would be possible if you tolerate a increased syncronisation latency 
 > > and a more complex detection state machine, but it's probably much 
 > > easier to add a frontend notifier to the demux which announces the 
 > > actual stream format. In this case change the notifier semantic so that 
 > > the passed argument is an enum 
 > > (LOCKED/UNLOCKED/STREAM_FMT_188BYTES/STREAM_FMT_204BYTES/STREAM_FMT_130BYTES) 
 > > instead of fe_status. Thenafter you need to export the 
 > > dvb_call_frontend_notifiers() function symbol so that it's accessible from 
 > > the lowlevel frontend driver.
 > 
 > There are no 204 byte TS packets, the extra bytes are read solomon
 > error correction data (which are useless for us). See EN 300 429.
 > 
 > What you did in your first "hack" was exactly the right thing to do:
 > - invert the sync byte if necessary
 > - discard the bytes after the 188th
 > 
 > IMHO there's no need to complicate the dvb-core layer because of this.
 > 
 > Johannes
 > 

There could be a problem if the presence of the error correction bytes
indicates that error correction has not been performed, so he may have
to add error correction before discarding the extra bytes.
All this should be done before feeding the data to the demux layer and
would not require a change of the core layer. 
In any case, it would be much better if the hardware can be persuaded
to do those things itself. 

Marcus

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| Dr. Marcus O.C. Metzler        |                                   |
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