[linux-dvb] Re: More V4 Demux API Q's

[Rob.McConnell@Zarlink.Com]

                      Johannes                                                                                                   
                      Stezenbach               To:       linux-dvb@linuxtv.org                                                   
                      <js@convergence.d        cc:                                                                               
                      e>                       Subject:  [linux-dvb] Re: More V4 Demux API Q's                                   
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                      12-Apr-2004 06:30                                                                                          
                      PM                                                                                                         
                                                                                                                                 
                                                                                                                                 










Hi Johannes,

Thanks for getting back to me on this ; )

> After some discussion we decided that the bandwidth handled by
> section filters is usually low, so that we can afford the overhead
> of keeping a flexible section filter layer in the driver core.

True.

> - one section filter per fd
> - multiple section filters for the same PID (on different fds)
> - section data is copied from hw DMA buffer of the PID filter
>   to the output buffer of the corresponding section filter fd

This certainly is more s/w + CPU overhead for h/w that has a single buffer
for all section filters associated with a common PID to drop into.

> Note: The (non-av7110) hw I know puts tags into the section ringbuffer
> of the PID filter, so software can determine which section filter
> matched.

The h/w that I am familiar with also performs tagging.  Is there any h/w
out there that actually has multiple section filters attached to a single
PID with a single h/w output buffer *WITHOUT* tagging?  If this were the
case, then it would make the task of demuxing the h/w circular buffer much
more CPU intensive/a nightmare.  I wonder if there is more h/w out there
that matches what I am used to rather than the AV7110?  If this were the
case, wouldn't it make more sense to support the majority of h/w rather
than legacy h/w such as the AV7110?

Incidentally, it looks as though I will have to diverge from the V4 API to
support customers who insist on having a single fd to read back all the
section tables associated with a single PID :(

Thanks Anyway,

Rob : )




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