Restore FFT module on main branch

rtl/ip/fft/DelayBuffer.v

@@ -0,0 +1,34 @@
+//----------------------------------------------------------------------
+//  DelayBuffer: Generate Constant Delay
+//----------------------------------------------------------------------
+module DelayBuffer #(
+    parameter   DEPTH = 32,
+    parameter   WIDTH = 16
+)(
+    input               clock,  //  Master Clock
+    input   [WIDTH-1:0] di_re,  //  Data Input (Real)
+    input   [WIDTH-1:0] di_im,  //  Data Input (Imag)
+    output  [WIDTH-1:0] do_re,  //  Data Output (Real)
+    output  [WIDTH-1:0] do_im   //  Data Output (Imag)
+);
+
+reg [WIDTH-1:0] buf_re[0:DEPTH-1];
+reg [WIDTH-1:0] buf_im[0:DEPTH-1];
+integer n;
+
+//  Shift Buffer
+/* verilator lint_off BLKLOOPINIT */
+always @(posedge clock) begin
+    for (n = DEPTH-1; n > 0; n = n - 1) begin
+        buf_re[n] <= buf_re[n-1];
+        buf_im[n] <= buf_im[n-1];
+    end
+    buf_re[0] <= di_re;
+    buf_im[0] <= di_im;
+end
+/* verilator lint_on BLKLOOPINIT */
+
+assign  do_re = buf_re[DEPTH-1];
+assign  do_im = buf_im[DEPTH-1];
+
+endmodule