I/o order – Altera FFT MegaCore Function User Manual
Page 33
Figure 3-7: Dynamically Changing the FFT Size
clock
reset_n
sink_valid
sink_ready
sink_sop
sink_eop
inverse
sink_real
sink_imag
source_real
source_imag
source_ready
source_valid
source_sop
source_eop
fftps
1. Change the size of the incoming FFT,
I/O Order
The I/O order determines order of samples entering and leaving the FFT and also determines if the FFT is
operating in engine-only mode or engine with bit-reversal or digit-reversal mode.
If the FFT operates in engine-only mode, the output data is available after approximately N + latency
clocks cycles after the first sample was input to the FFT. Latency represents a small latency through the
FFT core and depends on the transform size. For engine with bit-reversal mode, the output is available
after approximately 2N + latency cycles.
Figure 3-8: Data Flow—Engine-Only Mode
clk
reset_n
sink_valid
sink_ready
sink_sop
sink_eop
sink_real
sink_imag
source_real
source_imag
source_valid
source_sop
source_eop
3-10
I/O Order
UG-FFT
2014.12.15
Altera Corporation
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