Subversion Repositories mcs-4

`timescale 1ns / 1ps

`default_nettype none

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

//

// MCS-4 i4001 shared ROM storage

//

// This module emulates the Intel 4001 ROM storage. It is separate from

// the "i4001" module to make efficient use of FPGA block ram resources.

// One i4001_rom instantiation can be connected to multiple "i4001"

// modules via a rom_addr / rom_data bus.

//

// This file is part of the MCS-4 project hosted at OpenCores:

//      http://www.opencores.org/cores/mcs-4/

//

// Copyright © 2021 by Reece Pollack <rrpollack@opencores.org>

//

// These materials are provided under the Creative Commons

// "Attribution-NonCommercial-ShareAlike" (CC BY-NC-SA) Public License.

// They are NOT "public domain", and are protected by copyright.

//

// This work based on materials provided by Intel Corporation and

// others under the same license. See the file doc/License for

// details of this license.

//

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

module i4001_rom #(

    parameter       ROM_FILE    = "i4001-0.mem",

    parameter [3:0] ROM_NUMBER  = 4'd0,

    parameter       ROM_SIZE    = 2048

    ) (

    input  wire         sysclk,

    input  wire [11:0]  rom_addr,

    output reg  [ 7:0]  rom_data

    );

    (* rom_style="block" *)

    reg [7:0]   rom_array [0:ROM_SIZE-1];

    initial begin

        $readmemh (ROM_FILE, rom_array);

    end

    wire [11:0] array_addr = {rom_addr[11:8] - ROM_NUMBER,

                              rom_addr[ 7:0]};

    // Block RAMs have synchronous read ports

    // that require a clock to read the array

    always @(posedge sysclk) begin

        rom_data <= rom_array[array_addr];

    end

endmodule