Texas Instruments TMS320C64X - Manual (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
4
(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
4
(nx) − 1] + 6 * nx/4 + 36
Codesize 928 bytes