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

//

// Filename:    rxemin.v

//

// Project:     OpenArty, an entirely open SoC based upon the Arty platform

//

// Purpose:     To force the minimum received packet size of an ethernet frame

//              to be a minimum of 64 bytes.  Packets less than 64-bytes

//              (including CRC) need to be dropped.  This module handles that

//      logic.

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2016, 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

//

//

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

//

//

module rxemin(i_clk, i_ce, i_en, i_cancel, i_v, i_d, o_v, o_d, o_err);

        parameter       MINNIBBLES=120;

        localparam      LGNCOUNT=(MINNIBBLES<63)? 6

                                :((MINNIBBLES<127)? 7:((MINNIBBLES<255)? 8:9));

        input                   i_clk, i_ce, i_en, i_cancel;

        input                   i_v;    // Valid

        input           [3:0]    i_d;    // Data nibble

        output  reg             o_err;

        reg     last_v;

        reg     [(LGNCOUNT-1):0] r_ncnt;

        initial o_v = 1'b0;

        initial last_v = 1'b0;

        always @(posedge i_clk)

        if (i_ce)

        begin

                last_v <= i_v;

                if (((!i_v)&&(!o_v))||(i_cancel))

                begin

                        r_ncnt <= 0;

                        o_err  <= 0;

                end else if (i_v)

                begin

                        r_ncnt <= (r_ncnt<MINNIBBLES) ? r_ncnt+1'b1 : r_ncnt;

                end else if (last_v)

                        o_err <= (i_en)&&(r_ncnt < MINNIBBLES);

        end

endmodule