Some weeks ago I said that I had to write code to implement FFT in an 8052. Now FFT code is already running. I have written this version in C, it has been compliled using an IAR compiler and it works fine.
I use 64 samples, in signed int format, though I use only samples between -512 and 511.
The typical error in output spectrum amplitudes is about 0.1 %, due to rounding (I do not use floats, but integers).
The FFT computation takes about 0.3 seconds in an 8051 with a 12 MHz crystal (including the generation of an amplitudes array).
If anyone is interested, please send me an e-mail and I will send you the source code attached to my answer (free, of course).
Or I will send a copy to the Forum if the Administrator thinks it is worth.

I hope my work can be useful not only for me, but for other people too.

Regards,
Alfredo del Rio.