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

[John Ripley]

> From: Jens Prüfer [mailto:jens.pruefer at gmx.de]
> Sent: 19 March 2004 18:39
> To: vorbis-dev at xiph.org
> Subject: Re: [vorbis-dev] How many MIPS for Vorbis Decoder?
> 
...
> > If you're looking for ultra-low-cost that probably rules 
> out anything ARM
> > based. (Grumble - ARM cores are great but they're always too damn
> > expensive). You don't need anything as powerful (or expensive) as a
> > StrongARM, but there's plenty of other microcontrollers 
> around that might
> > do the job a bit less marginally. Don't forget development 
> time when you
> > compare these things for cost :)
> 
> OK, so which device would you chose for the lowest cost 
> solution? Since I also 
> want to implement part of an IP Stack on the same chip (there 
> is the uIP that 
> fits in 40k but again I have no idea how "expensive" that 
> implementation is 
> concerning CPU cycles), it has to leave a bit of headroom 
> when crunching on those DCT :)

I don't know much about the "ultra low cost" market. The only stuff I've
really played with is targetted for MP3 players in the first place, and
those are at least several times faster than the MSP430. It's usually just a
case of optimisation to get Vorbis to fit and run real time on them. For
arcane low power / low cost DSP architectures, it might be a case of never
fitting or running real time.

> There is the C2000 DSP/Microcontroller fusion series at TI 
> that has about 40 
> MIPS at an affordable price/1000 u. But it does not have to 
> be TI of course!

Sounds a bit more realistic, that one.

> I am so totally clueless (but that will change), I don't have 
> any idea about 
> memory usage either. You mentioned 128KB could be a hard 
> constraint? I was 
> hoping to get away cheap and just use the on board memory of 
> the Chip. Ok, go ahead, call me an idiot :)

There's a fairly large amount of RAM needed for the codebooks and MDCT
decoding. I don't know how much Tremor-lowmem is at these days, but I'd say
about 64-128KB. If you don't have the internal RAM available, you'll need
external RAM. And if it's an arcane DSP architecture, you'll probably need
to DMA external RAM on demand. Fun :)

> Just imagine a stand-alone IP ready device that has to decode 
> a mono UDP Vorbis stream as cheap as humanly possible.

I hate to say it, but I think a lower profile codec might be a better idea
than cramming Vorbis into an ultra-low-cost device. Something like Speex,
perhaps?

- John Ripley.
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