[maemo-developers] [maemo-developers] OGG support

[From: Nils Faerber]

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Clemens Eisserer schrieb:
> Hello,
>>Of course it is not fast enough for the standard Ogg Vorbis
>>decoder. But there exists an integer-only version called
>>Tremor (http://www.xiph.org/vorbis/) which is usable on the
>>device.
> What I wonder is that it seems FP is really slow on the Nokia770,
> although the ARM9 built in seems to support FP operations in hw.
> I am just a bit curious about that, any ideas why its still that slow?
> Take the fp-instructions that much cycles?

I am quite sure that the ARM9 does not support FP at all. What is IMHO
supported are some FP traps that would trap into kernel or other FP
software implementations. But that dies not speed up anything. There is
to my knowledge no embedded CPU that has hw FP built in.

All software FP implementations are of course very CPU intensive. You
have to calculate the FP result in software which takes several hundred
cycles while in hardware it would only take just a few cycles. So FP on
emebdded devices will probably always be dead slow - at least for the
next future.

Concerning OGG the Vorbis people took integer only into account from the
very early beginning of the development. As a result the finaly codec
was quite easy to be optimised for integer, the result is Tremor which
was released just a few weeks after final OGG/Vorbis release.

Concerning the 770 the integer version could be a first start for having
OGG capabilities at all. The OMAP DSP device is open to a certain
extend. The tools to develop code for it are freely available, some
documentation is too. The DSP in the 770 is controlled by the also free
DSP gateway project. So there is no big reason why there cannot be a
free DSP OGG code any time in the near future. I guess on of the major
problems here is that developing code for DSPs is not very well known in
the open source community... on the other that could be a very
interesting software project ;)

> lg Clemens
Cheers
  nils faerber

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