Hi Bonifacio,
> Is there a big difference of performance between GNU and VDSP compilers?
I'm going to give a slightly rubbish answer for this one: Basically, it depends on the code in question.
I've written a little about it in a post here:
But in short: GCC does a pretty good job at control code and floating point, but VDSP/CCES is typically going to produce faster code, especially for signal processing intensive code. Furthermore, GCC is primarily provided to enable Linux, so the bare metal tools don't have any of the drivers and system services that VDSP/CCES have.
Unfortunately, the only way to know for sure is to actually try both toolchains.
> Should it be possible to use the scratch RAM for code?
Unfortunately not. It can be used for stack and heap or (with a bit of trickery) zero init data.
Have you tried creating a map file to see what's taking up all the space (i think the command is: -Wl,-Map=a.map)?
Stu