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6065 Discussions

megacore fft 8.0 problem

Honored Contributor II

Hi everyone, 


i face a strange problem with megacore fft. 

The operation mode i used is 

burst mode, Quad output, 1024 points, 2 engines 

and the device is Cyclone II 

Quartus II v80sp1 


i have do a lots of testing for the fft megacore... 


first, i would like to read data from fifos which also the megacore produce from the wizard to be the fft inputs (include the real part and image part). 


i write control module (in Verilog) to handle the control signals between fifos and fft. 


in my design, the fft only accept one frame(1024 data samples) one time, so i need to use burst mode. i read user guide of FFT Megacore Function and understand that there is a small fifo buffer at the sink of the block. 

i write finite state machine to control sink_sop, sink_eop, sink_valid carefully, and watch the simulation result. 

it goes wrong! 


when the sink_ready is asserted, i asserted rdreq(fifo read enable signal) to read data from fifo, and then asserted sink_valid. 

sink_sop asserted only at the first data, sink_eop asserted only at the last data, and sink_valid asserted from sink_sop to sink_eop. 

there is no any source_error occurs in the process, but the source_real and source_image are wrong. :((the source_sop, source_eop and source_valid are OK, source_ready is asserted) <= the source_real and source_image come out, but the value is incorrect.  


more information i got, when i remove fifos and control module. only the fft megacore, and input the sink data from simulation(Vector waveform file). it works correctly!!! Why?:confused: 


anyone can do me a favor, please~ 


ps. attach files are the simulation results
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2 Replies
Honored Contributor II

Hi taylor, 


Can you tell me the clock you're using??
Honored Contributor II

Hello again, 


i'm having some problems with FFT megacore, because source_sop is never asserted and sink_ready is asserted just for a few clock's and then comes to low. 


i'm using a 30ns clock. 


I attach my simulator waveforms.