FFT Accelerator
6-8 ADSP-214xx SHARC Processor Hardware Reference
Internal Memory Storage
This section describes the required software buffers in internal memory
and the required storage model for data and coefficients using the FFT
accelerator.
Small FFT N<=256
To run a small FFT three buffers are required:
• Input Buffer [2 × N] packed or unpacked data
• Output Buffer [2 × N] packed or unpacked data
• Coefficient Buffer [2 × N]
Unpacked Data
If unpacked data is selected this is the required input format or output for-
mat. Programs can optionally select the input or output data streams to be
unpacked. In this mode, the first samples are all real followed by the imag-
inary samples.
RE[0], RE[1], ...RE[N-1], IM[0], IM[2], ... IM[N-1]
This can be independent for the input or output data streams.
Packed Data
The default format for packed data is as follows.
RE[0], IM[0], RE[1], IM[1], .... RE[N-1], IM[N-1]
Twiddles
The default format for coefficient buffer (twiddles) is as follows.
Re(CF[0]), Im(CF[0]), -Im(CF[0]), Re(CF[0]), Re(CF[1]),
Im(CF[1]), -Im(CF[1]), Re(CF[1]), .......... Re(CF[N/2-1]),
Im(CF[N/2-1]), -Im(CF[N/2-1]), Re(CF[N/2-1]) (4xN/2 = 2N words)
]
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