[vorbis-dev] How many MIPS for Vorbis Decoder?

[Dan Conti]

Note that this was just an example, one which i have worked with in the
past, but comments inline.

> -----Original Message-----
> From: owner-vorbis-dev at xiph.org [mailto:owner-vorbis-dev at xiph.org]On
> Behalf Of John Ripley
> Sent: Friday, March 19, 2004 4:51 PM
> To: vorbis-dev at xiph.org
> Subject: Re: [vorbis-dev] How many MIPS for Vorbis Decoder?
>
> The 7312 is a fantastic embedded CPU, but it's quite dated, and 48KB is
> way too little RAM. I believe the internal SRAM on the Cirrus 7312 is
> also half speed, and very many cycles to access. I ran some benchmarks
> on it a while back and discovered to my horror that it was about 5
> cycles random access and 2-3 cycles sequential depending on core clock
> speed. It wasn't actually worth the programming effort to put anything
> in internal RAM because cache was way faster, and internal vs external
> made very little difference to power consumption or performance.

There are AAC, WMA, and MP3 libraries available that require less than 24K
of ram; i was able to get each of these running on the on-chip ram on that
processor. Along with a relatively full fat filesystem, audio buffering,
simple UI, etc. For that part, SRAM is actually a saving grace, since random
access to sram is about half as many cycles as random access to sdram, but
still, it's not an ideal setup in many ways.

Do people really put more than ~50K of sram on chip these days? Guess i'm
out of the loop :)

> If all you want is to play a low quality stream, then 48KB might shave
> by, but you're looking at a LOT of optimisation and even then quality
> tradeoffs. Let's put it this way - having only 288KB of RAM and an
> arcane DSP architecure is what is preventing me from adding Vorbis
> support to the remaining Rio platforms out there are the moment. That's
> 288KB before a rather complex UI eats a chunk. It's possible to fit the
> rest, but it'll take way longer than my spare time :)

I just noticed you work at rio. I thought you guys switched to the 7312 for
most of your stuff? Maybe that was just a few of the handhelds. And that rio
boombox product that never came to be :)

I agree though, in general, if you have a complex UI to support it's going
to be difficult to fit it in a small memory footprint. Also i dont really
know how much ram tremor wants these days.

> I think over the next year we may see a lot of "MP3" player chips which
> have plenty of internal RAM, e.g 256KB+. Embedded DRAM (refreshed 1T)
> seems to be the next big thing. Makes my life easier anyway :)

I really doubt it. The success of the ipod mini throws the whole flash based
player market into question. Why would chip manufacturers add more on chip
ram, which results in significantly more expensive parts, when people are
buying HD based products which have off-chip memory for buffering?

>
> - John Ripley.
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