Brtdku

I am having problem understanding the following code (bimpy.v) that does unsigned 2-bit multiply operation.

Edit: Added comment from one of my friend: the following modification does the same thing with fewer logic !!

o_r <= (i_a[0] ? i_b : 0) + (i_a[1] ? i_b:0)<<1;

What are the purposes of the two signals (w_r and c) in bimpy.v ?

assign  w_r =  { ((i_a[1])?i_b:{(BW){1'b0}}), 1'b0 }

            ^ { 1'b0, ((i_a[0])?i_b:{(BW){1'b0}}) };



assign  c = { ((i_a[1])?i_b[(BW-2):0]:{(BW-1){1'b0}}) }

        & ((i_a[0])?i_b[(BW-1):1]:{(BW-1){1'b0}});

The code does not match the 2-bit by 2-bit binary multiplier gate-level diagram , please correct me if wrong

I am also attaching a working waveform from bimpy.v for a simple 2x2 unsigned multiplier.

I have also generated a gate-level representation diagram for bimpy.v

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

//

// Filename:    bimpy

//

// Project: A multiply core generator

//

// Purpose: An unsigned 2-bit multiply based upon the fact that LUT's allow

//      6-bits of input, but a 2x2 bit multiply will never carry more

//  than one bit.  While this multiply is hardware independent, it is

//  really motivated by trying to optimize for a specific piece of

//  hardware (Xilinx-7 series ...) that has 4-input LUT's with carry

//  chains.

//

// Creator: Dan Gisselquist, Ph.D.

//      Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2015,2017-2019, 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.  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

//

//

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

module  bimpy(i_clk, i_reset, i_ce, i_a, i_b, o_r);

    parameter   BW=2, LUTB=2;

    input               i_clk, i_reset, i_ce;

    input       [(LUTB-1):0]    i_a;

    input       [(BW-1):0]  i_b;

    output  reg [(BW+LUTB-1):0] o_r;



    wire    [(BW+LUTB-2):0] w_r;

    wire    [(BW+LUTB-3):1] c;



    assign  w_r =  { ((i_a[1])?i_b:{(BW){1'b0}}), 1'b0 }

                ^ { 1'b0, ((i_a[0])?i_b:{(BW){1'b0}}) };

    assign  c = { ((i_a[1])?i_b[(BW-2):0]:{(BW-1){1'b0}}) }

            & ((i_a[0])?i_b[(BW-1):1]:{(BW-1){1'b0}});



    initial o_r = 0;

    always @(posedge i_clk)

        if (i_reset)

            o_r <= 0;

        else if (i_ce)

            o_r <= w_r + { c, 2'b0 };



endmodule