[Tremor] Notes on Implementing Tremor on an ARM7TDMI CPU

[Segher Boessenkool]

> Ah, thanks. This is an ARM7TDMI which is listed as an ARMv4T. I'm not
> srue what the T stands for,

It means it supports Thumb.

> I'd like to do some profiling on x86 as that would give me a clue  
> but I
> had trouble getting gcc -pg to output valid information.

If you have a Mac, try Shark.  On Linux, oprofile will help.  But
gprof should work fine as well, dunno what you're doing wrong.

*But*: the performance characteristics of something like Tremor will
be *very* different on high-end CPUs -- for example, FFT takes
comparatively more time on low-end "embedded" CPUs, while the codebook
decoding is very fast on those.

> Interesting, it seems to also be an ARMv4T. I wonder why I'm having
> issues then.

You need to measure.  There could be thousands of things wrong.

> Well, that sounds like plenty of performance. I will keep tweaking.
> There are just so many variables and it takes ages to try them all.  
> For
> all I know, -O2 or -Os may give me a big boost over -O3.

Yes, you should use -Os by default, only use other options when you
know they improve performance on a certain piece of code.

Good luck,


Segher