Subversion Repositories dblclockfft

////////////////////////////////////////////////////////////////////////////////

//

// Filename:    bldstage.cpp

//

// Project:     A General Purpose Pipelined FFT Implementation

//

// Purpose:     

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

////////////////////////////////////////////////////////////////////////////////

//

// Copyright (C) 2015-2018, Gisselquist Technology, LLC

//

// This program is free software (firmware): you can redistribute it and/or

// modify it under the terms of  the GNU General Public License as published

// by the Free Software Foundation, either version 3 of the License, or (at

// your option) any later version.

//

// This program is distributed in the hope that it will be useful, but WITHOUT

// ANY WARRANTY; without even the implied warranty of MERCHANTIBILITY or

// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

//

// You should have received a copy of the GNU General Public License along

// with this program.  (It's in the $(ROOT)/doc directory, run make with no

// target there if the PDF file isn't present.)  If not, see

// <http://www.gnu.org/licenses/> for a copy.

//

// License:     GPL, v3, as defined and found on www.gnu.org,

//              http://www.gnu.org/licenses/gpl.html

//

//

////////////////////////////////////////////////////////////////////////////////

//

//

#define _CRT_SECURE_NO_WARNINGS   //  ms vs 2012 doesn't like fopen

#include <stdio.h>

#include <stdlib.h>

#ifdef _MSC_VER //  added for ms vs compatibility

#include <io.h>

#include <direct.h>

#define _USE_MATH_DEFINES

#else

// And for G++/Linux environment

#include <unistd.h>     // Defines the R_OK/W_OK/etc. macros

#endif

#include <string.h>

#include <string>

#include <math.h>

#include <ctype.h>

#include <assert.h>

#include "defaults.h"

#include "legal.h"

#include "fftlib.h"

#include "rounding.h"

#include "bldstage.h"

void    build_dblstage(const char *fname, ROUND_T rounding,

                        const bool async_reset, const bool dbg) {

        FILE    *fp = fopen(fname, "w");

        if (NULL == fp) {

                fprintf(stderr, "Could not open \'%s\' for writing\n", fname);

                perror("O/S Err was:");

                return;

        }

        const   char    *rnd_string;

        if (rounding == RND_TRUNCATE)

                rnd_string = "truncate";

        else if (rounding == RND_FROMZERO)

                rnd_string = "roundfromzero";

        else if (rounding == RND_HALFUP)

                rnd_string = "roundhalfup";

        else

                rnd_string = "convround";

        std::string     resetw("i_reset");

        if (async_reset)

                resetw = std::string("i_areset_n");

        fprintf(fp,

SLASHLINE

"//\n"

"// Filename:\tlaststage%s.v\n"

"//\n"

"// Project:\t%s\n"

"//\n"

"// Purpose:\tThis is part of an FPGA implementation that will process\n"

"//             the final stage of a decimate-in-frequency FFT, running\n"

"//     through the data at two samples per clock.  If you notice from the\n"

"//     derivation of an FFT, the only time both even and odd samples are\n"

"//     used at the same time is in this stage.  Therefore, other than this\n"

"//     stage and these twiddles, all of the other stages can run two stages\n"

"//     at a time at one sample per clock.\n"

"//\n"

"// Operation:\n"

"//     Given a stream of values, operate upon them as though they were\n"

"//     value pairs, x[2n] and x[2n+1].  The stream begins when n=0, and ends\n"

"//     when n=1.  When the first x[0] value enters, the synchronization\n"

"//     input, i_sync, must be true as well.\n"

"//\n"

"//     For this stream, produce outputs\n"

"//     y[2n  ] = x[2n] + x[2n+1], and\n"

"//     y[2n+1] = x[2n] - x[2n+1]\n"

"//\n"

"//     When y[0] is output, a synchronization bit o_sync will be true as\n"

"//     well, otherwise it will be zero.\n"

"//\n"

"//\n"

"//     In this implementation, the output is valid one clock after the input\n"

"//     is valid.  The output also accumulates one bit above and beyond the\n"

"//     number of bits in the input.\n"

"//\n"

"//             i_clk   A system clock\n", (dbg)?"_dbg":"", prjname);

        if (async_reset)

                fprintf(fp,

"//             i_areset_n      An active low asynchronous reset\n");

        else

                fprintf(fp,

"//             i_reset A synchronous reset\n");

        fprintf(fp,

"//             i_ce    Circuit enable--nothing happens unless this line is high\n"

"//             i_sync  A synchronization signal, high once per FFT at the start\n"

"//             i_left  The first (even) complex sample input.  The higher order\n"

"//                     bits contain the real portion, low order bits the\n"

"//                     imaginary portion, all in two\'s complement.\n"

"//             i_right The next (odd) complex sample input, same format as\n"

"//                     i_left.\n"

"//             o_left  The first (even) complex output.\n"

"//             o_right The next (odd) complex output.\n"

"//             o_sync  Output synchronization signal.\n"

"//\n%s"

"//\n", creator);

        fprintf(fp, "%s", cpyleft);

        fprintf(fp, "//\n//\n`default_nettype\tnone\n//\n");

        fprintf(fp,

"module\tlaststage%s(i_clk, %s, i_ce, i_sync, i_left, i_right, o_left, o_right, o_sync%s);\n"

        "\tparameter\tIWIDTH=%d,OWIDTH=IWIDTH+1, SHIFT=%d;\n"

        "\tinput\t\ti_clk, %s, i_ce, i_sync;\n"

        "\tinput\t\t[(2*IWIDTH-1):0]\ti_left, i_right;\n"

        "\toutput\treg\t[(2*OWIDTH-1):0]\to_left, o_right;\n"

        "\toutput\treg\t\t\to_sync;\n"

        "\n", (dbg)?"_dbg":"", resetw.c_str(), (dbg)?", o_dbg":"",

        TST_DBLSTAGE_IWIDTH, TST_DBLSTAGE_SHIFT,

                resetw.c_str());

        if (dbg) { fprintf(fp, "\toutput\twire\t[33:0]\t\t\to_dbg;\n"

                "\tassign\to_dbg = { ((o_sync)&&(i_ce)), i_ce, o_left[(2*OWIDTH-1):(2*OWIDTH-16)],\n"

                        "\t\t\t\t\to_left[(OWIDTH-1):(OWIDTH-16)] };\n"

"\n");

        }

        fprintf(fp,

        "\twire\tsigned\t[(IWIDTH-1):0]\ti_in_0r, i_in_0i, i_in_1r, i_in_1i;\n"

        "\tassign\ti_in_0r = i_left[(2*IWIDTH-1):(IWIDTH)];\n"

        "\tassign\ti_in_0i = i_left[(IWIDTH-1):0];\n"

        "\tassign\ti_in_1r = i_right[(2*IWIDTH-1):(IWIDTH)];\n"

        "\tassign\ti_in_1i = i_right[(IWIDTH-1):0];\n"

        "\twire\t[(OWIDTH-1):0]\t\to_out_0r, o_out_0i,\n"

                                "\t\t\t\t\to_out_1r, o_out_1i;\n"

"\n"

"\n"

        "\t// Handle a potential rounding situation, when IWIDTH>=OWIDTH.\n"

"\n"

"\n");

        fprintf(fp,

        "\n"

        "\t// As with any register connected to the sync pulse, these must\n"

        "\t// have initial values and be reset on the %s signal.\n"

        "\t// Other data values need only restrict their updates to i_ce\n"

        "\t// enabled clocks, but sync\'s must obey resets and initial\n"

        "\t// conditions as well.\n"

        "\treg\trnd_sync, r_sync;\n"

"\n"

        "\tinitial\trnd_sync      = 1\'b0; // Sync into rounding\n"

        "\tinitial\tr_sync        = 1\'b0; // Sync coming out\n",

                resetw.c_str());

        if (async_reset)

                fprintf(fp, "\talways @(posedge i_clk, negdge i_areset_n)\n\t\tif (!i_areset_n)\n");

        else

                fprintf(fp, "\talways @(posedge i_clk)\n\t\tif (i_reset)\n");

        fprintf(fp,

                "\t\tbegin\n"

                        "\t\t\trnd_sync <= 1\'b0;\n"

                        "\t\t\tr_sync <= 1\'b0;\n"

                "\t\tend else if (i_ce)\n"

                "\t\tbegin\n"

                        "\t\t\trnd_sync <= i_sync;\n"

                        "\t\t\tr_sync <= rnd_sync;\n"

                "\t\tend\n"

"\n"

        "\t// As with other variables, these are really only updated when in\n"

        "\t// the processing pipeline, after the first i_sync.  However, to\n"

        "\t// eliminate as much unnecessary logic as possible, we toggle\n"

        "\t// these any time the i_ce line is enabled, and don\'t reset.\n"

        "\t// them on %s.\n", resetw.c_str());

        fprintf(fp,

        "\t// Don't forget that we accumulate a bit by adding two values\n"

        "\t// together. Therefore our intermediate value must have one more\n"

        "\t// bit than the two originals.\n"

        "\treg\tsigned\t[(IWIDTH):0]\trnd_in_0r, rnd_in_0i;\n"

        "\treg\tsigned\t[(IWIDTH):0]\trnd_in_1r, rnd_in_1i;\n\n"

        "\talways @(posedge i_clk)\n"

                "\t\tif (i_ce)\n"

                "\t\tbegin\n"

                        "\t\t\t//\n"

                        "\t\t\trnd_in_0r <= i_in_0r + i_in_1r;\n"

                        "\t\t\trnd_in_0i <= i_in_0i + i_in_1i;\n"

                        "\t\t\t//\n"

                        "\t\t\trnd_in_1r <= i_in_0r - i_in_1r;\n"

                        "\t\t\trnd_in_1i <= i_in_0i - i_in_1i;\n"

                        "\t\t\t//\n"

                "\t\tend\n"

"\n");

        fprintf(fp,

        "\t%s #(IWIDTH+1,OWIDTH,SHIFT) do_rnd_0r(i_clk, i_ce,\n"

        "\t\t\t\t\t\t\trnd_in_0r, o_out_0r);\n\n", rnd_string);

        fprintf(fp,

        "\t%s #(IWIDTH+1,OWIDTH,SHIFT) do_rnd_0i(i_clk, i_ce,\n"

        "\t\t\t\t\t\t\trnd_in_0i, o_out_0i);\n\n", rnd_string);

        fprintf(fp,

        "\t%s #(IWIDTH+1,OWIDTH,SHIFT) do_rnd_1r(i_clk, i_ce,\n"

        "\t\t\t\t\t\t\trnd_in_1r, o_out_1r);\n\n", rnd_string);

        fprintf(fp,

        "\t%s #(IWIDTH+1,OWIDTH,SHIFT) do_rnd_1i(i_clk, i_ce,\n"

        "\t\t\t\t\t\t\trnd_in_1i, o_out_1i);\n\n", rnd_string);

        fprintf(fp, "\n"

        "\t// Prior versions of this routine did not include the extra\n"

        "\t// clock and register/flip-flops that this routine requires.\n"

        "\t// These are placed in here to correct a bug in Verilator, that\n"

        "\t// otherwise struggles.  (Hopefully this will fix the problem ...)\n"

        "\talways @(posedge i_clk)\n"

                "\t\tif (i_ce)\n"

                "\t\tbegin\n"

                        "\t\t\to_left  <= { o_out_0r, o_out_0i };\n"

                        "\t\t\to_right <= { o_out_1r, o_out_1i };\n"

                "\t\tend\n"

"\n"

        "\tinitial\to_sync = 1\'b0; // Final sync coming out of module\n");

        if (async_reset)

                fprintf(fp, "\talways @(posedge i_clk, negdge i_areset_n)\n\t\tif (!i_areset_n)\n");

        else

                fprintf(fp, "\talways @(posedge i_clk)\n\t\tif (i_reset)\n");

        fprintf(fp,

                "\t\t\to_sync <= 1\'b0;\n"

                "\t\telse if (i_ce)\n"

                "\t\t\to_sync <= r_sync;\n"

"\n"

"endmodule\n");

        fclose(fp);

}

void    build_stage(const char *fname,

                int stage, int nwide, int offset,

                int nbits, int xtra, int ckpce,

                const bool async_reset, const bool dbg) {

        FILE    *fstage = fopen(fname, "w");

        int     cbits = nbits + xtra;

        std::string     resetw("i_reset");

        if (async_reset)

                resetw = std::string("i_areset_n");

        if (((unsigned)cbits * 2u) >= sizeof(long long)*8) {

                fprintf(stderr, "ERROR: CMEM Coefficient precision requested overflows long long data type.\n");

                exit(-1);

        }

        if (fstage == NULL) {

                fprintf(stderr, "ERROR: Could not open %s for writing!\n", fname);

                perror("O/S Err was:");

                fprintf(stderr, "Attempting to continue, but this file will be missing.\n");

                return;

        }

        fprintf(fstage,

SLASHLINE

"//\n"

"// Filename:\tfftstage%s.v\n"

"//\n"

"// Project:\t%s\n"

"//\n"

"// Purpose:\tThis file is (almost) a Verilog source file.  It is meant to\n"

"//             be used by a FFT core compiler to generate FFTs which may be\n"

"//     used as part of an FFT core.  Specifically, this file encapsulates\n"

"//     the options of an FFT-stage.  For any 2^N length FFT, there shall be\n"

"//     (N-1) of these stages.\n"

"//\n"

"//\n"

"// Operation:\n"

"//     Given a stream of values, operate upon them as though they were\n"

"//     value pairs, x[n] and x[n+N/2].  The stream begins when n=0, and ends\n"

"//     when n=N/2-1 (i.e. there's a full set of N values).  When the value\n"

"//     x[0] enters, the synchronization input, i_sync, must be true as well.\n"

"//\n"

"//     For this stream, produce outputs\n"

"//     y[n    ] = x[n] + x[n+N/2], and\n"

"//     y[n+N/2] = (x[n] - x[n+N/2]) * c[n],\n"

"//                     where c[n] is a complex coefficient found in the\n"

"//                     external memory file COEFFILE.\n"

"//     When y[0] is output, a synchronization bit o_sync will be true as\n"

"//     well, otherwise it will be zero.\n"

"//\n"

"//     Most of the work to do this is done within the butterfly, whether the\n"

"//     hardware accelerated butterfly (uses a DSP) or not.\n"

"//\n%s"

"//\n",

                (dbg)?"_dbg":"", prjname, creator);

        fprintf(fstage, "%s", cpyleft);

        fprintf(fstage, "//\n//\n`default_nettype\tnone\n//\n");

        fprintf(fstage, "module\tfftstage%s(i_clk, %s, i_ce, i_sync, i_data, o_data, o_sync%s);\n",

                (dbg)?"_dbg":"", resetw.c_str(),

                (dbg)?", o_dbg":"");

        // These parameter values are useless at this point--they are to be

        // replaced by the parameter values in the calling program.  Only

        // problem is, the CWIDTH needs to match exactly!

        fprintf(fstage, "\tparameter\tIWIDTH=%d,CWIDTH=%d,OWIDTH=%d;\n",

                nbits, 20, nbits+1); // 20, not cbits, since the tb depends upon it

        fprintf(fstage,

"\t// Parameters specific to the core that should be changed when this\n"

"\t// core is built ... Note that the minimum LGSPAN (the base two log\n"

"\t// of the span, or the base two log of the current FFT size) is 3.\n"

"\t// Smaller spans (i.e. the span of 2) must use the dbl laststage module.\n"

"\tparameter\tLGWIDTH=%d, LGSPAN=%d, BFLYSHIFT=0;\n"

"\tparameter\t[0:0]     OPT_HWMPY = 1;\n",

                lgval(stage), (nwide <= 1) ? lgval(stage)-1 : lgval(stage)-2);

        fprintf(fstage,

"\t// Clocks per CE.  If your incoming data rate is less than 50%% of your\n"

"\t// clock speed, you can set CKPCE to 2\'b10, make sure there's at least\n"

"\t// one clock between cycles when i_ce is high, and then use two\n"

"\t// multiplies instead of three.  Setting CKPCE to 2\'b11, and insisting\n"

"\t// on at least two clocks with i_ce low between cycles with i_ce high,\n"

"\t// then the hardware optimized butterfly code will used one multiply\n"

"\t// instead of two.\n"

"\tparameter\t  CKPCE = %d;\n", ckpce);

        fprintf(fstage,

"\t// The COEFFILE parameter contains the name of the file containing the\n"

"\t// FFT twiddle factors\n");

        if (nwide == 2) {

                fprintf(fstage, "\tparameter\tCOEFFILE=\"cmem_%c%d.hex\";\n",

                        (offset)?'o':'e', stage*2);

        } else

                fprintf(fstage, "\tparameter\tCOEFFILE=\"cmem_%d.hex\";\n",

                        stage);

        fprintf(fstage,"\n"

"`ifdef VERILATOR\n"

        "\tparameter [0:0] ZERO_ON_IDLE = 1'b0;\n"

"`else\n"

        "\tlocalparam [0:0] ZERO_ON_IDLE = 1'b0;\n"

"`endif // VERILATOR\n\n");

        fprintf(fstage,

"\tinput                                        i_clk, %s, i_ce, i_sync;\n"

"\tinput                [(2*IWIDTH-1):0]        i_data;\n"

"\toutput       reg     [(2*OWIDTH-1):0]        o_data;\n"

"\toutput       reg                             o_sync;\n"

"\n", resetw.c_str());

        if (dbg) { fprintf(fstage, "\toutput\twire\t[33:0]\t\t\to_dbg;\n"

                "\tassign\to_dbg = { ((o_sync)&&(i_ce)), i_ce, o_data[(2*OWIDTH-1):(2*OWIDTH-16)],\n"

                        "\t\t\t\t\to_data[(OWIDTH-1):(OWIDTH-16)] };\n"

"\n");

        }

        fprintf(fstage,

"\treg  wait_for_sync;\n"

"\treg  [(2*IWIDTH-1):0]        ib_a, ib_b;\n"

"\treg  [(2*CWIDTH-1):0]        ib_c;\n"

"\treg  ib_sync;\n"

"\n"

"\treg  b_started;\n"

"\twire ob_sync;\n"

"\twire [(2*OWIDTH-1):0]\tob_a, ob_b;\n");

        fprintf(fstage,

"\n"

"\t// cmem is defined as an array of real and complex values,\n"

"\t// where the top CWIDTH bits are the real value and the bottom\n"

"\t// CWIDTH bits are the imaginary value.\n"

"\t//\n"

"\t// cmem[i] = { (2^(CWIDTH-2)) * cos(2*pi*i/(2^LGWIDTH)),\n"

"\t//           (2^(CWIDTH-2)) * sin(2*pi*i/(2^LGWIDTH)) };\n"

"\t//\n"

"\treg  [(2*CWIDTH-1):0]        cmem [0:((1<<LGSPAN)-1)];\n"

"\tinitial\t$readmemh(COEFFILE,cmem);\n\n");

        // gen_coeff_file(coredir, fname, stage, cbits, nwide, offset, inv);

        fprintf(fstage,

"\treg  [(LGSPAN):0]            iaddr;\n"

"\treg  [(2*IWIDTH-1):0]        imem    [0:((1<<LGSPAN)-1)];\n"

"\n"

"\treg  [LGSPAN:0]              oB;\n"

"\treg  [(2*OWIDTH-1):0]        omem    [0:((1<<LGSPAN)-1)];\n"

"\n"

"\tinitial wait_for_sync = 1\'b1;\n"

"\tinitial iaddr = 0;\n");

        if (async_reset)

                fprintf(fstage, "\talways @(posedge i_clk, negedge i_areset_n)\n\t\tif (!i_areset_n)\n");

        else

                fprintf(fstage, "\talways @(posedge i_clk)\n\t\tif (i_reset)\n");

        fprintf(fstage,

        "\tbegin\n"

                "\t\t\twait_for_sync <= 1\'b1;\n"

                "\t\t\tiaddr <= 0;\n"

        "\tend else if ((i_ce)&&((!wait_for_sync)||(i_sync)))\n"

        "\tbegin\n"

                "\t\t//\n"

                "\t\t// First step: Record what we\'re not ready to use yet\n"

                "\t\t//\n"

                "\t\tiaddr <= iaddr + { {(LGSPAN){1\'b0}}, 1\'b1 };\n"

                "\t\twait_for_sync <= 1\'b0;\n"

        "\tend\n"

        "\talways @(posedge i_clk) // Need to make certain here that we don\'t read\n"

        "\tif ((i_ce)&&(!iaddr[LGSPAN])) // and write the same address on\n"

                "\t\timem[iaddr[(LGSPAN-1):0]] <= i_data; // the same clk\n"

        "\n");

        fprintf(fstage,

        "\t//\n"

        "\t// Now, we have all the inputs, so let\'s feed the butterfly\n"

        "\t//\n"

        "\tinitial ib_sync = 1\'b0;\n");

        if (async_reset)

                fprintf(fstage, "\talways @(posedge i_clk, negedge i_areset_n)\n\tif (!i_areset_n)\n");

        else

                fprintf(fstage, "\talways @(posedge i_clk)\n\tif (i_reset)\n");

        fprintf(fstage,

                        "\t\tib_sync <= 1\'b0;\n"

                "\telse if (i_ce)\n"

                "\tbegin\n"

                        "\t\t// Set the sync to true on the very first\n"

                        "\t\t// valid input in, and hence on the very\n"

                        "\t\t// first valid data out per FFT.\n"

                        "\t\tib_sync <= (iaddr==(1<<(LGSPAN)));\n"

                "\tend\n\n"

        "\talways\t@(posedge i_clk)\n"

        "\tif (i_ce)\n"

        "\tbegin\n"

                "\t\t// One input from memory, ...\n"

                "\t\tib_a <= imem[iaddr[(LGSPAN-1):0]];\n"

                "\t\t// One input clocked in from the top\n"

                "\t\tib_b <= i_data;\n"

                "\t\t// and the coefficient or twiddle factor\n"

                "\t\tib_c <= cmem[iaddr[(LGSPAN-1):0]];\n"

        "\tend\n\n");

        fprintf(fstage,

        "\t// The idle register is designed to keep track of when an input\n"

        "\t// to the butterfly is important and going to be used.  It's used\n"

        "\t// in a flag following, so that when useful values are placed\n"

        "\t// into the butterfly they'll be non-zero (idle=0), otherwise when\n"

        "\t// the inputs to the butterfly are irrelevant and will be ignored,\n"

        "\t// then (idle=1) those inputs will be set to zero.  This\n"

        "\t// functionality is not designed to be used in operation, but only\n"

        "\t// within a Verilator simulation context when chasing a bug.\n"

        "\t// In this limited environment, the non-zero answers will stand\n"

        "\t// in a trace making it easier to highlight a bug.\n"

        "\treg  idle;\n"

        "\tgenerate if (ZERO_ON_IDLE)\n"

        "\tbegin\n"

                "\t\tinitial    idle = 1;\n"

                "\t\talways @(posedge i_clk)\n"

                "\t\tif (i_reset)\n"

                        "\t\t\tidle <= 1\'b1;\n"

                "\t\telse if (i_ce)\n"

                        "\t\t\tidle <= (!iaddr[LGSPAN])&&(!wait_for_sync);\n\n"

        "\tend else begin\n\n"

        "\t\talways @(*) idle = 0;\n\n"

        "\tend endgenerate\n\n");

        fprintf(fstage,

"\tgenerate if (OPT_HWMPY)\n"

"\tbegin : HWBFLY\n"

"\t\thwbfly #(.IWIDTH(IWIDTH),.CWIDTH(CWIDTH),.OWIDTH(OWIDTH),\n"

                        "\t\t\t\t.CKPCE(CKPCE), .SHIFT(BFLYSHIFT))\n"

                "\t\t\tbfly(i_clk, %s, i_ce, (idle)?0:ib_c,\n"

                        "\t\t\t\t(idle || (!i_ce)) ? 0:ib_a,\n"

                        "\t\t\t\t(idle || (!i_ce)) ? 0:ib_b,\n"

                        "\t\t\t\t(ib_sync)&&(i_ce),\n"

                        "\t\t\t\tob_a, ob_b, ob_sync);\n"

"\tend else begin : FWBFLY\n"

"\t\tbutterfly #(.IWIDTH(IWIDTH),.CWIDTH(CWIDTH),.OWIDTH(OWIDTH),\n"

                "\t\t\t\t.CKPCE(CKPCE),.SHIFT(BFLYSHIFT))\n"

        "\t\t\tbfly(i_clk, %s, i_ce,\n"

                        "\t\t\t\t\t(idle||(!i_ce))?0:ib_c,\n"

                        "\t\t\t\t\t(idle||(!i_ce))?0:ib_a,\n"

                        "\t\t\t\t\t(idle||(!i_ce))?0:ib_b,\n"

                        "\t\t\t\t\t(ib_sync&&i_ce),\n"

                        "\t\t\t\t\tob_a, ob_b, ob_sync);\n"

"\tend endgenerate\n\n",

                        resetw.c_str(), resetw.c_str());

        fprintf(fstage,

        "\t//\n"

        "\t// Next step: recover the outputs from the butterfly\n"

        "\t//\n"

        "\tinitial oB        = 0;\n"

        "\tinitial o_sync    = 0;\n"

        "\tinitial b_started = 0;\n");

        if (async_reset)

                fprintf(fstage, "\talways @(posedge i_clk, negedge i_areset_n)\n\t\tif (!i_areset_n)\n");

        else

                fprintf(fstage, "\talways @(posedge i_clk)\n\t\tif (i_reset)\n");

        fprintf(fstage,

        "\tbegin\n"

                "\t\toB <= 0;\n"

                "\t\to_sync <= 0;\n"

                "\t\tb_started <= 0;\n"

        "\tend else if (i_ce)\n"

        "\tbegin\n"

        "\t\to_sync <= (!oB[LGSPAN])?ob_sync : 1\'b0;\n"

        "\t\tif (ob_sync||b_started)\n"

                "\t\t\toB <= oB + { {(LGSPAN){1\'b0}}, 1\'b1 };\n"

        "\t\tif ((ob_sync)&&(!oB[LGSPAN]))\n"

                "\t\t// A butterfly output is available\n"

                        "\t\t\tb_started <= 1\'b1;\n"

        "\tend\n\n");

        fprintf(fstage,

        "\treg  [(LGSPAN-1):0]\t\tdly_addr;\n"

        "\treg  [(2*OWIDTH-1):0]\tdly_value;\n"

        "\talways @(posedge i_clk)\n"

        "\tif (i_ce)\n"

        "\tbegin\n"

        "\t\tdly_addr <= oB[(LGSPAN-1):0];\n"

        "\t\tdly_value <= ob_b;\n"

        "\tend\n"

        "\talways @(posedge i_clk)\n"

        "\tif (i_ce)\n"

                "\t\tomem[dly_addr] <= dly_value;\n"

"\n");

        fprintf(fstage,

        "\talways @(posedge i_clk)\n"

        "\tif (i_ce)\n"

        "\t\to_data <= (!oB[LGSPAN])?ob_a : omem[oB[(LGSPAN-1):0]];\n"

"\n");

        fprintf(fstage, "endmodule\n");

}