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

//

// Filename:    memdev.v

//

// Project:     CMod S6 System on a Chip, ZipCPU demonstration Project

//

// Purpose:     This file is really simple: it creates an on-chip memory,

//              accessible via the wishbone bus, that can be used in this

//      project.  The memory has single cycle access--although getting to the

//      memory from the ZipCPU may cost another cycle or two in access.  Either

//      way, operations can be pipelined for greater speed.

//

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Technology, LLC

//

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

//

// Copyright (C) 2015-2017, 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  memdev(i_clk, i_wb_cyc, i_wb_stb, i_wb_we, i_wb_addr, i_wb_data, i_wb_sel,

                o_wb_ack, o_wb_stall, o_wb_data);

        parameter       LGMEMSZ=15, DW=32, EXTRACLOCK= 0;

        localparam      AW = LGMEMSZ - 2;

        input                           i_clk, i_wb_cyc, i_wb_stb, i_wb_we;

        input           [(AW-1):0]       i_wb_addr;

        input           [(DW-1):0]       i_wb_data;

        input           [(DW/8-1):0]     i_wb_sel;

        output  reg                     o_wb_ack;

        output  wire                    o_wb_stall;

        output  reg     [(DW-1):0]       o_wb_data;

        wire                    w_wstb, w_stb;

        wire    [(DW-1):0]       w_data;

        wire    [(AW-1):0]       w_addr;

        wire    [(DW/8-1):0]     w_sel;

        generate

        if (EXTRACLOCK == 0)

        begin

                assign  w_wstb = (i_wb_stb)&&(i_wb_we);

                assign  w_stb  = i_wb_stb;

                assign  w_addr = i_wb_addr;

                assign  w_data = i_wb_data;

                assign  w_sel  = i_wb_sel;

        end else begin

                reg             last_wstb, last_stb;

                always @(posedge i_clk)

                        last_wstb <= (i_wb_stb)&&(i_wb_we);

                always @(posedge i_clk)

                        last_stb <= (i_wb_stb);

                reg     [(AW-1):0]       last_addr;

                reg     [(DW-1):0]       last_data;

                reg     [(DW/8-1):0]     last_sel;

                always @(posedge i_clk)

                        last_data <= i_wb_data;

                always @(posedge i_clk)

                        last_addr <= i_wb_addr;

                always @(posedge i_clk)

                        last_sel <= i_wb_sel;

                assign  w_wstb = last_wstb;

                assign  w_stb  = last_stb;

                assign  w_addr = last_addr;

                assign  w_data = last_data;

                assign  w_sel  = last_sel;

        end endgenerate

        reg     [(DW-1):0]       mem     [0:((1<<AW)-1)];

        always @(posedge i_clk)

                o_wb_data <= mem[w_addr];

        always @(posedge i_clk)

        begin

                if ((w_wstb)&&(w_sel[3]))

                        mem[w_addr][31:24] <= w_data[31:24];

                if ((w_wstb)&&(w_sel[2]))

                        mem[w_addr][23:16] <= w_data[23:16];

                if ((w_wstb)&&(w_sel[1]))

                        mem[w_addr][15: 8] <= w_data[15:8];

                if ((w_wstb)&&(w_sel[0]))

                        mem[w_addr][ 7: 0] <= w_data[7:0];

        end

        always @(posedge i_clk)

                o_wb_ack <= (w_stb);

        assign  o_wb_stall = 1'b0;

endmodule