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

//                                                              //

//  Memory Access - Instantiates the memory access stage        //

//  sub-modules of the Amber 25 Core                            //

//                                                              //

//  This file is part of the Amber project                      //

//  http://www.opencores.org/project,amber                      //

//                                                              //

//  Description                                                 //

//  Instantiates the Data Cache                                 //

//  Also contains a little bit of logic to decode memory        //

//  accesses to decide if they are cached or not                //

//                                                              //

//  Author(s):                                                  //

//      - Conor Santifort, csantifort.amber@gmail.com           //

//                                                              //

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

//                                                              //

// Copyright (C) 2011 Authors and OPENCORES.ORG                 //

//                                                              //

// This source file may be used and distributed without         //

// restriction provided that this copyright statement is not    //

// removed from the file and that any derivative work contains  //

// the original copyright notice and the associated disclaimer. //

//                                                              //

// This source file is free software; you can redistribute it   //

// and/or modify it under the terms of the GNU Lesser General   //

// Public License as published by the Free Software Foundation; //

// either version 2.1 of the License, or (at your option) any   //

// later version.                                               //

//                                                              //

// This source is distributed in the hope that it will be       //

// useful, but WITHOUT ANY WARRANTY; without even the implied   //

// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      //

// PURPOSE.  See the GNU Lesser General Public License for more //

// details.                                                     //

//                                                              //

// You should have received a copy of the GNU Lesser General    //

// Public License along with this source; if not, download it   //

// from http://www.opencores.org/lgpl.shtml                     //

//                                                              //

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

module a25_mem

(

input                       i_clk,

input                       i_fetch_stall,          // Fetch stage asserting stall

output                      o_mem_stall,            // Mem stage asserting stall

input       [31:0]          i_daddress,

input                       i_daddress_valid,

input       [31:0]          i_daddress_nxt,         // un-registered version of address to the cache rams

input       [31:0]          i_write_data,

input                       i_write_enable,

input                       i_exclusive,            // high for read part of swap access

input       [3:0]           i_byte_enable,

input       [7:0]           i_exec_load_rd,         // The destination register for a load instruction

input                       i_cache_enable,         // cache enable

input                       i_cache_flush,          // cache flush

input       [31:0]          i_cacheable_area,       // each bit corresponds to 2MB address space

output      [31:0]          o_mem_read_data,

output                      o_mem_read_data_valid,

output      [9:0]           o_mem_load_rd,          // The destination register for a load instruction

// Wishbone accesses                                                         

output                      o_wb_cached_req,        // Cached Request

output                      o_wb_uncached_req,      // Unached Request

output                      o_wb_qword,             // High for a quad-word read request

output                      o_wb_write,             // Read=0, Write=1

output     [3:0]            o_wb_byte_enable,       // byte eable

output     [31:0]           o_wb_write_data,

output     [31:0]           o_wb_address,           // wb bus                                 

input      [31:0]           i_wb_read_data,         // wb bus                              

input                       i_wb_cached_ready,      // wishbone access complete and read data valid

input                       i_wb_uncached_ready     // wishbone access complete and read data valid

);

`include "memory_configuration.v"

wire    [31:0]              cache_read_data;

wire                        address_cachable;

wire                        sel_cache_p;

wire                        sel_cache;

wire                        cached_wb_req;

wire                        uncached_data_access;

wire                        uncached_data_access_p;

wire                        cache_stall;

wire                        uncached_wb_wait;

reg                         uncached_wb_req_r = 'd0;

reg                         uncached_wb_stop_r = 'd0;

reg                         cached_wb_stop_r = 'd0;

wire                        daddress_valid_p;  // pulse

reg      [31:0]             mem_read_data_r = 'd0;

reg                         mem_read_data_valid_r = 'd0;

reg      [9:0]              mem_load_rd_r = 'd0;

wire     [9:0]              mem_load_rd_c;

wire    [31:0]              mem_read_data_c;

wire                        mem_read_data_valid_c;

reg                         mem_stall_r = 'd0;

wire                        use_mem_reg;

reg                         fetch_only_stall_r = 'd0;

wire                        fetch_only_stall;

wire                        void_output;

wire                        wb_stop;

reg                         daddress_valid_stop_r = 'd0;

// ======================================

// Memory Decode

// ======================================

assign address_cachable         = in_cachable_mem( i_daddress ) && i_cacheable_area[i_daddress[25:21]];

assign sel_cache_p              = daddress_valid_p && address_cachable && i_cache_enable && !i_exclusive;

assign sel_cache                = i_daddress_valid && address_cachable && i_cache_enable && !i_exclusive;

assign uncached_data_access     = i_daddress_valid && !sel_cache   && !(cache_stall);

assign uncached_data_access_p   = daddress_valid_p && !sel_cache   && !(cache_stall);

assign use_mem_reg              = wb_stop && !mem_stall_r;

assign o_mem_read_data          = use_mem_reg ? mem_read_data_r       : mem_read_data_c;

assign o_mem_load_rd            = use_mem_reg ? mem_load_rd_r         : mem_load_rd_c;

assign o_mem_read_data_valid    = !void_output && (use_mem_reg ? mem_read_data_valid_r : mem_read_data_valid_c);

// Return read data either from the wishbone bus or the cache

assign mem_read_data_c          = sel_cache             ? cache_read_data :

                                  uncached_data_access  ? i_wb_read_data  :

                                                          32'h76543210    ;

assign mem_load_rd_c            = {i_daddress[1:0], i_exec_load_rd};

assign mem_read_data_valid_c    = i_daddress_valid && !i_write_enable && !o_mem_stall;

assign o_mem_stall              = uncached_wb_wait || cache_stall;

// Request wishbone access

assign o_wb_byte_enable         = i_byte_enable;

assign o_wb_write               = i_write_enable;

assign o_wb_address             = {i_daddress[31:2], 2'd0};

assign o_wb_write_data          = i_write_data;

assign o_wb_cached_req          = !cached_wb_stop_r && cached_wb_req;

assign o_wb_uncached_req        = !uncached_wb_stop_r && uncached_data_access_p;

assign o_wb_qword               = !cached_wb_stop_r && cached_wb_req && !i_write_enable;

assign uncached_wb_wait         = (o_wb_uncached_req || uncached_wb_req_r) && !i_wb_uncached_ready;

always @( posedge i_clk )

    begin

    uncached_wb_req_r <=  (o_wb_uncached_req || uncached_wb_req_r) && !i_wb_uncached_ready;

    end

assign fetch_only_stall     = i_fetch_stall && !o_mem_stall;

always @( posedge i_clk )

    fetch_only_stall_r <= fetch_only_stall;

assign void_output = (fetch_only_stall_r && fetch_only_stall) || (fetch_only_stall_r && mem_read_data_valid_r);

// pulse this signal

assign daddress_valid_p = i_daddress_valid && !daddress_valid_stop_r;

always @( posedge i_clk )

    begin

    uncached_wb_stop_r      <= (uncached_wb_stop_r || uncached_data_access_p) && (i_fetch_stall || o_mem_stall);

    cached_wb_stop_r        <= (cached_wb_stop_r   || cached_wb_req)          && (i_fetch_stall || o_mem_stall);

    daddress_valid_stop_r   <= (daddress_valid_stop_r || daddress_valid_p)    && (i_fetch_stall || o_mem_stall);

    // hold this until the mem access completes

    mem_stall_r <= o_mem_stall;

    end

assign wb_stop = uncached_wb_stop_r || cached_wb_stop_r;

always @( posedge i_clk )

    if ( !wb_stop || o_mem_stall )

        begin

        mem_read_data_r         <= mem_read_data_c;

        mem_load_rd_r           <= mem_load_rd_c;

        mem_read_data_valid_r   <= mem_read_data_valid_c;

        end

// ======================================

// L1 Data Cache

// ======================================

a25_dcache u_dcache (

    .i_clk                      ( i_clk                 ),

    .i_fetch_stall              ( i_fetch_stall         ),

    .o_stall                    ( cache_stall           ),

    .i_request                  ( sel_cache_p           ),

    .i_exclusive                ( i_exclusive           ),

    .i_write_data               ( i_write_data          ),

    .i_write_enable             ( i_write_enable        ),

    .i_address                  ( i_daddress            ),

    .i_address_nxt              ( i_daddress_nxt        ),

    .i_byte_enable              ( i_byte_enable         ),

    .i_cache_enable             ( i_cache_enable        ),

    .i_cache_flush              ( i_cache_flush         ),

    .o_read_data                ( cache_read_data       ),

    .o_wb_req                   ( cached_wb_req         ),

    .i_wb_read_data             ( i_wb_read_data        ),

    .i_wb_ready                 ( i_wb_cached_ready     )

);

endmodule