[linux-dvb] Re: LinuxDVB V4 API questions (3)

[Alasdair FARMER <alasdair.farmer@st.com>]

> >  
> > I also think that using the demux for memory input does not make much
> > sense. Usually you have demux unit with several demuxes and several
> > inputs and each demux can choose the input it wants to use, 
> > including memory input. 
> > So, the "frontend" devices, whether there is an actual frontend, 
> > memory DMA hardware or something else connected to it (other parallel
> > or serial inputs from other devices), should correspond to these
> > inputs.
> 
> Both solutions (playback trough demux or playback through memory 
> frontend device) are basically the same, but with one exception.
> 
> Suppose you have 1 "memory frontend", two demuxes and two decoding units 
> in hardware. If you make the playback through a memory frontend, then 
> for certain hardware it's possible to connect the output of 
> the frontend to both demuxes and both demuxes to one mpeg decoder each.
> 
> This may be not possible if you playback the data through the demux 
> directly, because usually you cannot connect both mpeg 
> decoders to one demux.
> 
> If it comes to dedicated firewire inputs and other nice things, it 
> really might be worth to extend the "memory frontend" approach.
> 
> > These devices should then offer calls for rate control as some memory 
> > DMA interfaces offer them and other calls for other hardware like 
> > firewire, etc. The question is how general you want to make this. 
> > Should the device enumerate capabilities and possible settings (like 
> > e.g. V4L2 devices) or is it enough to support a standard set of input 
> > devices?
> 
> Hm, I'm not sure. I'm currently reconstructing the frontend handling in 
> dvb-core for the v4 api, so I'm going to enfore the memory frontend 
> stuff to see how it's going to be.
> 
> > Ralph
> 
> CU
> Michael.
> 

Sounds promising...  For our purposes we have no option but to feed data in
through a frontend, our hardware does not allow writing directly to the
demux.  A demux takes an input from a frontend, that frontend might have as
its source either a tuner, data fed directly to an IO port (we refer to this
as a SW transport stream) or a 1394 port.

We have no other way to deal with 'memory frontends', in addition,
obviously, the CA is directly coupled to the data passing through the demux
hardware - so we couldn't fake something up either.

Ali.




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