Texas Instruments TMS320C64X Manuel d'utilisateur télécharger pdf (Page 57)

DSP_fft32x32s

4-29 C64x+ DSPLIB Reference

The FFT coefficients (twiddle factors) are generated using the program

tw_fft32x32 provided in the directory ‘support\fft’. The scale factor must be

1073741823.5. The input data must be scaled by 2

(log2(nx)

−

ceil[

log4(nx)−1

])

to completely prevent overflow.

Implementation Notes

- Bank Conflicts: No bank conflicts occur.

- Interruptibility: The code is interruptible.

- Scaling is performed at each stage by shifting the results right by 1,

preventing overflow.

- The routine uses log

(nx) − 1 stages of radix-4 transform and performs

either a radix-2 or radix-4 transform on the last stage depending on nx. If

nx is a power of 4, then this last stage is also a radix-4 transform, otherwise

it is a radix-2 transform.

- See the fft16x16t implementation notes, as similar ideas are used.

Benchmarks Cycles (13 * nx/8 + 36) * ceil[log

(nx) − 1] + 6 * nx/4 + 36

Codesize 928 bytes

1 2 ... 52 53 54 55 56 57 58 59 60 61 62 ... 168 169

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Texas Instruments TMS320C64X Manuel d'utilisateur Page 57