>So I think I may have confused my terminology a bit. In any case, what I am
>trying to do was recompile the Linux kernel to use the THUMB instruction
>subset (ARM v4T), since the ARM website boasts a potential for 30% reduction
>in code size.
You currently need a completely separate compiler to generate Thumb code
rather than ARM code - you must configure as `thumb-linux' or something
similar. I don't think it will currently work to just compile the kernel as
Thumb code, though I would be happy to help you if you want to try to get it
going.
>So I don't see the 30% savings here. Is it possible that I need to
>recompile my GCC with different settings (does the strongarm110 option not
>do THUMB)? Or do you think the 1.15% savings is all I'm going to get out of
>it?
The ARM architecture manual contains details of what each level of the
architecture includes, which might help to clear up the confusion. Briefly,
ARMv3 is what you might call the "base" instruction set. ARMv4 adds long
multiply, signed byte and halfword load and store instructions. Thumb is
pretty much orthogonal to this and you can add it to either a v3 or v4
implementation, giving you v3T or v4T. There are a bunch of other extensions
to ARMv3 as well (eg the D, M and I from ARM7TDMI).
The StrongARM-1 core is a v4 implementation. So no, the strongarm110 option
doesn't turn Thumb on; it just enables the v4 instructions such as LDRH.
1.15% saving sounds about right for that, in fact it's slightly higher than
I'd have expected.
p.
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