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iWMMXt processor uses CP0 and CP1 while FPA uses CP1 and CP2, which causes iWMMXt processor not compatible with FPA. So to support floating point in iWMMXt, we cannot use FPA, but VFP or EABI.
My understanding is EABI provides another implementation to IEEE-754 spec, similar to VFP. Does anyone know what the performance of VFP and EABI are?
I've managed to confuse myself a bit here; there is no iWMMXt processor with hardware FP. However iWMMXt processors are incompatible with FPA due to opcode overlap, while they could have an VFP co-processor in principal. That said iWMMXt instructions should make softfloat fairly quick anyway.
So the result is if you want use software using the FPA ABI (oldABI requires "hard" FPA) support you can't target iWMMXt and have to use ARMv5t instead unless the software in question was built with softfloat, it should work ok on a iWMMXt targetted system in that case.
If anybody knows better please let me know.
Steve
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