Occasional Contributor
Regular ContributorHi Jim,
For your information, I have found out why after digit reversal, your expected data is appearing at index 16 instead of 32. With your FFT configuration, the Radix-4 digit reversal is implied but not Radix-2. You can refer to System Messages at the bottom of your FFT configuration screenshot for the Radix-4 implied.
In your case, the spike is originally at index 4 (Radix-4 = 0010), after digit reversal, it become 0100 which is equivalent to digit-reversed index of 16 which tally with your simulation. As for the other spike at index 252, the digit-reversed index = 63 which tally with your simulation as well. Hope this explain.
Please let me know if there is any concern. Thank you.
Best regards,
Chee Pin
Occasional ContributorHi Chee pin,
thanks for your effort.
I am not quite understand it.
Can you suggest how can I turn the digit reversed result back into natural order output using my 8 bits index? because I plan to turn result into natural order result in FPGA and forward it to next stream for further usage.
my current logic is
assign digi_reverse_index[fft_result_address_width-1:0] ={result_index[0], result_index[1], result_index[2], result_index[3],
result_index[4], result_index[5], result_index[6], result_index[7]};
integer i;
always @(posedge clk or negedge reset_n)
begin
if(!reset_n)
begin
for (i = 0; i < data_num-1; i = i + 1) begin
fft_digireverse_result_r[i] <= 32'd0;
fft_digireverse_result_i[i] <= 32'd0;
end
end
else if(source_valid) begin
fft_digireverse_result_r[digi_reverse_index] <=source_real ;
fft_digireverse_result_i[digi_reverse_index] <=source_imag ;
end
end
thanks
Jim
Occasional ContributorI put form here to summary up, I am not sure with the same data source how can I use digit reverse output to figure out the target frequency .
