[speex-dev] Introduction...

A. J. Baker Andrew at teledesign.co.uk
Wed Feb 19 12:02:44 PST 2003

> 3. I'm interested in the methodology for creating a fixed point
> implementation and guaging how "good" it is relative to the floating 
> point golden standard

My methodology at this stage is to get it working on the floating point 
DSP first and to gain recent experience in both Speex and the TI DSP 
range while I do so. Then I'll enter into serious discussions about the 
fixed point version - see below.

> 4. I think the codec is portable to more fixed point embedded devices 
> if you stick to C rather than C++ code.  If you follow the TI XDAIS 
> standard you'll wind up creating an object-oriented codec but you can 
> do it all in C (Relocatable, re-entrant code, state structure, etc.). 
>  Who knows you might want to run it on an embedded DSP that doesn't 
> support C++ someday.

<p>I doubt I will. Others might :-)

More specifically - the manufacturer of VoIP cards I refer to earlier 
build their current cards using fixed point DSPS (although they use 
floating point DSPs (Sharc) elsewhere in their range. They have a number 
of seriously talented and very well equipped DSP programmers in their 
staff - their business depends on how much they can squeeze out of every 
DSP. If suceeded in getting them interested it would be good.

I personally would prefer working in C rather than C++. But my choices 
might be limited. :-)

I'll come back to this point when all the TI stuff arrives and I've 
looked through it all. I've just had notification it has been despatched.

> 5. You should take a close look at the intrinsic definitions on the 
> 55x when making your (the?) integer implementation.  When you port to 
> the 55x you can substitute the intrinsics and get alot of MIPS 
> reduction right away.  We've seen alot of similar intrinsics on other 
> (non-TI) DSPs too.

OK. Noted.

I've also been told by a TI applications BOD that although the 55x is a 
fixed point device, it does contain some internal features which speed 
up running floating point code. This was done to meet certain 
requirements in the Mobile market and they suspect that there may be 
enough computing power to running a floating point codec on the 55x.

Again when I've got this working on the 6711, it will be much easier to 
come back to this using some of the TI tools to tell me how good (or 
bad) it is going to be. I might not have an immediate need to do a true, 
full "fixed point" port at all.

An issue to consider is why we want a fixed-point port. I suspect we/you 
do. But I'd currently hate to have to justify that suspicion rigourously.

<p><p><p>--- >8 ----
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