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

//

// Filename:    pipemem.v

//

// Project:     Zip CPU -- a small, lightweight, RISC CPU soft core

//

// Purpose:     A memory unit to support a CPU, this time one supporting

//              pipelined wishbone memory accesses.  The goal is to be able

//      to issue one pipelined wishbone access per clock, and (given the memory

//      is fast enough) to be able to read the results back at one access per

//      clock.  This renders on-chip memory fast enough to handle single cycle

//      (pipelined) access.

//

//

// Creator:     Dan Gisselquist, Ph.D.

//              Gisselquist Tecnology, LLC

//

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

//

// Copyright (C) 2015, 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.

//

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

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

//

//

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

//

module  pipemem(i_clk, i_rst, i_pipe_stb,

                i_op, i_addr, i_data, i_oreg,

                        o_busy, o_pipe_stalled, o_valid, o_err, o_wreg, o_result,

                o_wb_cyc_gbl, o_wb_cyc_lcl,

                        o_wb_stb_gbl, o_wb_stb_lcl,

                        o_wb_we, o_wb_addr, o_wb_data,

                i_wb_ack, i_wb_stall, i_wb_err, i_wb_data);

        parameter       ADDRESS_WIDTH = 24, AW=ADDRESS_WIDTH;

        input                   i_clk, i_rst;

        input                   i_pipe_stb;

        // CPU interface

        input                   i_op;

        input           [31:0]   i_addr;

        input           [31:0]   i_data;

        input           [4:0]    i_oreg;

        // CPU outputs

        output  wire            o_busy;

        output  wire            o_pipe_stalled;

        output  reg             o_valid;

        output  reg             o_err;

        output  reg     [4:0]    o_wreg;

        output  reg     [31:0]   o_result;

        // Wishbone outputs

        output  reg             o_wb_cyc_gbl, o_wb_stb_gbl;

        output  reg             o_wb_cyc_lcl, o_wb_stb_lcl, o_wb_we;

        output  reg     [(AW-1):0]       o_wb_addr;

        output  reg     [31:0]   o_wb_data;

        // Wishbone inputs

        input                   i_wb_ack, i_wb_stall, i_wb_err;

        input           [31:0]   i_wb_data;

        reg     [3:0]            rdaddr, wraddr;

        wire    [3:0]            nxt_rdaddr;

        reg     [(5-1):0]        fifo_oreg [0:15];

        initial rdaddr = 0;

        initial wraddr = 0;

        always @(posedge i_clk)

                fifo_oreg[wraddr] <= i_oreg;

        always @(posedge i_clk)

                if ((i_rst)||(i_wb_err))

                        wraddr <= 0;

                else if (i_pipe_stb)

                        wraddr <= wraddr + 4'h1;

        always @(posedge i_clk)

                if ((i_rst)||(i_wb_err))

                        rdaddr <= 0;

                else if ((i_wb_ack)&&(cyc))

                        rdaddr <= rdaddr + 4'h1;

        assign  nxt_rdaddr = rdaddr + 4'h1;

        reg     cyc;

        wire    gbl_stb, lcl_stb;

        assign  lcl_stb = (i_addr[31:8]==24'hc00000)&&(i_addr[7:5]==3'h0);

        assign  gbl_stb = (~lcl_stb);

                        //= ((i_addr[31:8]!=24'hc00000)||(i_addr[7:5]!=3'h0));

        initial cyc = 0;

        initial o_wb_cyc_lcl = 0;

        initial o_wb_cyc_gbl = 0;

        always @(posedge i_clk)

                if (i_rst)

                begin

                        o_wb_cyc_gbl <= 1'b0;

                        o_wb_cyc_lcl <= 1'b0;

                        o_wb_stb_gbl <= 1'b0;

                        o_wb_stb_lcl <= 1'b0;

                        cyc <= 1'b0;

                end else if (cyc)

                begin

                        if ((~i_wb_stall)&&(~i_pipe_stb))

                        begin

                                o_wb_stb_gbl <= 1'b0;

                                o_wb_stb_lcl <= 1'b0;

                        // end else if ((i_pipe_stb)&&(~i_wb_stall))

                        // begin

                                // o_wb_addr <= i_addr[(AW-1):0];

                                // o_wb_data <= i_data;

                        end

                        if (((i_wb_ack)&&(nxt_rdaddr == wraddr))||(i_wb_err))

                        begin

                                o_wb_cyc_gbl <= 1'b0;

                                o_wb_cyc_lcl <= 1'b0;

                                cyc <= 1'b0;

                        end

                end else if (i_pipe_stb) // New memory operation

                begin // Grab the wishbone

                        o_wb_cyc_lcl <= lcl_stb;

                        o_wb_cyc_gbl <= gbl_stb;

                        o_wb_stb_lcl <= lcl_stb;

                        o_wb_stb_gbl <= gbl_stb;

                        cyc <= 1'b1;

                        // o_wb_addr <= i_addr[(AW-1):0];

                        // o_wb_data <= i_data;

                        // o_wb_we <= i_op

                end

        always @(posedge i_clk)

                if ((cyc)&&(i_pipe_stb)&&(~i_wb_stall))

                begin

                        o_wb_addr <= i_addr[(AW-1):0];

                        o_wb_data <= i_data;

                end else if ((~cyc)&&(i_pipe_stb))

                begin

                        o_wb_addr <= i_addr[(AW-1):0];

                        o_wb_data <= i_data;

                end

        always @(posedge i_clk)

                if ((i_pipe_stb)&&(~cyc))

                        o_wb_we   <= i_op;

        initial o_valid = 1'b0;

        always @(posedge i_clk)

                o_valid <= (cyc)&&(i_wb_ack)&&(~o_wb_we);

        initial o_err = 1'b0;

        always @(posedge i_clk)

                o_err <= (cyc)&&(i_wb_err);

        assign  o_busy = cyc;

        always @(posedge i_clk)

                o_wreg <= fifo_oreg[rdaddr];

        always @(posedge i_clk)

                if (i_wb_ack)

                        o_result <= i_wb_data;

        assign  o_pipe_stalled = (cyc)

                        &&((i_wb_stall)||((~o_wb_stb_lcl)&&(~o_wb_stb_gbl)));

endmodule