Optimisation of CMSIS constants for cortex M4

[prasannanaik]

Hi,

I am using CMSIS library for FFT computation in LPC54607J256BD208E.

IDE: MCXpresso IDE v 10.3.1_2233

I am trying to optimize my code size to fit a bootloader along with application code.

On analysis of Map size, I found that cmsis fft constants take up a lot spcae.

Constants	Size
twiddleCoef_2048	16384
twiddleCoef_rfft_4096	16384
twiddleCoef_rfft_2048	8192
twiddleCoef_1024	8192
armBitRevIndexTable2048	7616
twiddleCoef_512	4096
twiddleCoef_rfft_1024	4096
armBitRevIndexTable1024	3600
twiddleCoef_256	2048
twiddleCoef_rfft_512	2048
Total	72656

Is there any way to optimize these constants or is there any code optimized fft library for this microcontroller.

Thanks and best regards,

Prasanna

[frank_m]

> Is there any way to optimize these constants or is there any code optimized fft library for this microcontroller.

Optimize for what ? You can either optimize for speed, for size, or a mixture (=compromise) of both.

The usage of the named pre-calculated constants for FFT is a speed optimization of that algorithm.

You can try implementing any other FFT algorithm, if you wish. But be aware of the limitations of "float" versus "double".