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/*

 * Memory Harness with Wishbone Slave interface

 *

 * (C) Copyleft 2007 Simply RISC LLP

 * AUTHOR: Fabrizio Fazzino <fabrizio.fazzino@srisc.com>

 *

 * LICENSE:

 * This is a Free Hardware Design; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * version 2 as published by the Free Software Foundation.

 * The above named program 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 General Public License for more details.

 *

 * DESCRIPTION:

 * Filename is a parameter, and the corresponding file content

 * must follow the rules stated in Verilog standard for the

 * $readmemh() system task.

 * For instance if you don't change the default name you just

 * have to put a text file named "memory.hex" in your simulation

 * directory with the following content inside:

 *

 *   // We start from address zero by default:

 *   1234567812345678

 *   FEDCBA9876543210

 *   // Now we jump to doubleword number 10 (i.e. address 80):

 *   @ 10

 *   02468ACE13579BDF

 *

 * This memory harness was originally based upon a Wishbone Slave

 * model written by Rudolf Usselmann <rudi@asics.ws> but now I've

 * written it again entirely from scratch.

 */

module mem_harness (

    sys_clock_i, sys_reset_i,

    wbs_addr_i, wbs_data_i, wbs_data_o, wbs_cycle_i, wbs_strobe_i,

    wbs_sel_i, wbs_we_i, wbs_ack_o

  );

  // System inputs

  input         sys_clock_i;     // System Clock

  input         sys_reset_i;     // System Reset

  // Wishbone Slave interface inputs

  input         wbs_cycle_i;     // Wishbone Cycle

  input         wbs_strobe_i;    // Wishbone Strobe

  input[63:0]   wbs_addr_i;      // Wishbone Address

  input[63:0]   wbs_data_i;      // Wishbone Data Input

  input         wbs_we_i;        // Wishbone Write Enable

  input[7:0]    wbs_sel_i;       // Wishbone Byte Select

  // Wishbone Slave interface registered outputs

  output        wbs_ack_o;       // Wishbone Ack

  reg           wbs_ack_o;       // Wishbone Ack

  output[63:0]  wbs_data_o;      // Wishbone Data Output

  reg[63:0]     wbs_data_o;      // Wishbone Data Output

  // Parameters

  parameter     addr_bits = 20;

  parameter     addr_max = (1<<addr_bits)-1;

  parameter     memfilename = "memory.hex";

  parameter     memdefaultcontent = 64'h0000000000000000;

  // Wires

  reg[63:0]     mem[addr_max:0];       // This is the memory!

  wire[63:0]    tmp_rd;                // Temporary read data

  wire[63:0]    tmp_wd;                // Temporary write data

  integer       i;                     // Index

  // Initialization

`ifdef DEBUG

  initial begin

    $display("INFO: MEMH %m: Memory Harness with Wishbone Slave interface starting...");

    $display("INFO: MEMH %m: %0d Address Bits / %0d Doublewords / %0d Bytes Total Memory", addr_bits, addr_max+1, (addr_max+1)*8);

    for(i=0; i<=addr_max; i=i+1) mem[i] = memdefaultcontent;

    $readmemh(memfilename, mem);

    $display("INFO: MEMH %m: Memory initialization completed");

  end

`endif

  // Assignments

  assign tmp_rd = mem[wbs_addr_i[addr_bits+2:3]];

  assign tmp_wd[63:56] = !wbs_sel_i[7] ? tmp_rd[63:56] : wbs_data_i[63:56];

  assign tmp_wd[55:48] = !wbs_sel_i[6] ? tmp_rd[55:48] : wbs_data_i[55:48];

  assign tmp_wd[47:40] = !wbs_sel_i[5] ? tmp_rd[47:40] : wbs_data_i[47:40];

  assign tmp_wd[39:32] = !wbs_sel_i[4] ? tmp_rd[39:32] : wbs_data_i[39:32];

  assign tmp_wd[31:24] = !wbs_sel_i[3] ? tmp_rd[31:24] : wbs_data_i[31:24];

  assign tmp_wd[23:16] = !wbs_sel_i[2] ? tmp_rd[23:16] : wbs_data_i[23:16];

  assign tmp_wd[15:08] = !wbs_sel_i[1] ? tmp_rd[15:08] : wbs_data_i[15:08];

  assign tmp_wd[07:00] = !wbs_sel_i[0] ? tmp_rd[07:00] : wbs_data_i[07:00];

  // Process the requests

  always @(posedge sys_clock_i) begin

    // Read cycle

    if(wbs_cycle_i & wbs_strobe_i & !wbs_we_i) begin

      // Return the ack

      wbs_ack_o = 1;

      // Return the data (ignore the byte select for reads)

      wbs_data_o = tmp_rd;

      // Write a comment

`ifdef DEBUG

      if(wbs_sel_i) $display("INFO: MEMH %m: R @ %t ns, AD=%X SEL=%X DAT=%X", $time, wbs_addr_i, wbs_sel_i, wbs_data_o);

`endif

    // Write cycle

    end else if(wbs_cycle_i & wbs_strobe_i & wbs_we_i) begin

      // Return the ack

      wbs_ack_o = 1;

      // Clear the output data

      wbs_data_o = 64'hZZZZZZZZZZZZZZZZ;

      // Store the data

      mem[wbs_addr_i[addr_bits+2:3]] = tmp_wd;

      // Write a comment

`ifdef DEBUG

      if(wbs_sel_i) $display("INFO: MEMH %m: W @ %t ns, AD=%X SEL=%X DAT=%X", $time, wbs_addr_i, wbs_sel_i, tmp_wd);

`endif

    // No read/write cycle

    end else begin

      // Clear the ack

      wbs_ack_o = 0;

      // Clear the output data

      wbs_data_o = 64'hZZZZZZZZZZZZZZZZ;

    end

  end

endmodule