[linux-dvb] DVB API update

Manu Abraham abraham.manu at gmail.com
Tue Sep 18 14:54:40 CEST 2007


Georg Acher wrote:
> On Tue, Sep 18, 2007 at 03:33:25PM +0400, Manu Abraham wrote:
>  
>>> I have h.264 playback running on a really slow Geode with 300MHz. For a
>>> 15Mbit/s stream, the TS path from the DMA buffers into user space needs
>>> about 5% CPU with traditional memcpy(). I wouldn't call that optimization
>>> worthy... What really counts is the postprocessing in user space (remuxing,
>>> repacking, etc.). The API may support this with single PIDs per
>>> read filedescriptor, but I don't think it makes a difference where the data
>>> is actually filtered...
>>>
>> You are looking at a single DVB-S2 demod. There are dual S2 demods in a
>> single chip config.
>> Consider that with multiple adapters, even if you ignore post processing.
> 
> But you wouldn't use a 300MHz CPU for that anyway, because it has no CPU
> power to do something else with the stream. I'm certainly the last who is
> against optimization, but I don't see the case here to put much effort in
> that.

Consider a situation, even for a STB (I am not stating that a STB is the
only application)

Dual config demod cores on a single chip, the device having more than
one demod. This results in a minimum of 4 streams, with the remux
overhead considered (i am not saying here is that it will kill your
embedded CPU) but it will *be* a significant overhead.




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