Altera FFT MegaCore Function Manuale Utente Scaricare il pdf (Pagina 30)

When the FFT completes the transform of the input block, it asserts source_valid and outputs the

complex transform domain data block in natural order. The FFT function asserts source_sop to

indicate the first output sample.

Figure 3-5: FFT Streaming Data Flow Output Flow Control

clk

source_real

source_imag

exponent_out

source_ready

source_valid

source_sop

source_eop

[0] X

[1]

[2]

[3]

[5]

[6]

[7] X

[8]

[10]

[11]

[12]

[9]

[0]

[1] X

[2]

[3]

[5] X

[6] X

[7] X

[8] X

[11]

[12]

EXP0

[4]

[9]

[4]

[10]

After N data transfers, the FFT asserts source_eop to indicate the end of the output data block

Enabling the Streaming FFT

1. You must assert the sink_valid signal for the FFT to assert source_valid (and a valid data output).

2. To extract the final frames of data from the FFT, you need to provide several frames where the

sink_valid signal is asserted and apply the sink_sop and sink_eop signals in accordance with the

Avalon-ST specification.

Variable Streaming

The variable streaming FFT allows continuous streaming of input data and produces a continuous stream

of output data similar to the streaming FFT. With the variable streaming FFT, the transform length

represents the maximum transform length. You can perform all transforms of length 2m where 6 < m <

log2(transform length) at runtime.

Changing Block Size

To change the size of the FFT on a block-by-block basis, change the value of the fftpts simultaneously

with the application of the sink_sop pulse (concurrent with the first input data sample of the block).

fftpts uses a binary representation of the size of the transform, therefore for a block with maximum

transfer size of 1,024. Table 3-2 shows the value of the fftpts signal and the equivalent transform size.

Table 3-2: fftpts and Transform Size

fftpts Transform Size

10000000000 1,024

01000000000 512

00100000000 256

00010000000 128

UG-FFT

2014.12.15

Enabling the Streaming FFT

3-7

FFT IP Core Functional Description

Altera Corporation

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