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`timescale 1ns / 1ps

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

// IBM 650 Reconstruction in Verilog (i650)

// 

// This file is part of the IBM 650 Reconstruction in Verilog (i650) project

// http:////www.opencores.org/project,i650

//

// Description: General storage.

// 

// Additional Comments: Drum storage is implemented as an array of 24000 5-bit

//  digits. An array address is formed by decoding the static portion of the

//  bi-quinary address into an origin (a multiple of 600), then adding the 

//  dynamic portion of the address (range 0..599).

//

// Copyright (c) 2015 Robert Abeles

//

// 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

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

`include "defines.v"

module gen_store (

   input rst,

   input ap, dp,

   input write_gate,

   input [0:6] addr_th, addr_h, addr_t,

   input [0:9] dynamic_addr,

   input [0:4] gs_in,

   input [0:14] console_ram_addr,

   input console_read_gs, console_write_gs,

   output reg[0:4] gs_out,

   output double_write, no_write

   );

   reg [0:4] gs_mem [0:32767];   // Rounded size up from 24000 to next 2^n. 

   //-----------------------------------------------------------------------------

   // Calculate the early (next digit) and on-time RAM addresses. Console read

   // and write are implementation extensions.

   //-----------------------------------------------------------------------------

   wire [0:14] band_addr, gs_addr, gs_addr_early;

   ram_band_addr rba(addr_th, addr_h, addr_t, band_addr);

   wire console_acc = console_read_gs | console_write_gs;

   assign gs_addr = console_acc? console_ram_addr : (band_addr + dynamic_addr);

   // The % operator fixes a spurious warning from XST synthesis due to use of a

   // 32-bit mux for ? operator. Uses no gates. 

   assign gs_addr_early = (console_acc? console_ram_addr

                        : (band_addr + ((dynamic_addr + 1) % 600))) % 32768;

   //-----------------------------------------------------------------------------

   // These 650 write errors are not possible for this implementation.

   //-----------------------------------------------------------------------------

   assign double_write = 0;

   assign no_write = 0;

   //-----------------------------------------------------------------------------

   // A : Read from RAM at on-time address.

   //-----------------------------------------------------------------------------

   always @(posedge ap) begin

      if (rst) begin

         gs_out <= `biq_blank;

      end else begin

         gs_out <= gs_mem[gs_addr];

      end

   end;

   //-----------------------------------------------------------------------------

   // D : Write to RAM at early address.

   //-----------------------------------------------------------------------------

   always @(posedge dp) begin

      if (write_gate)

         gs_mem[gs_addr_early] <= gs_in;

   end;

endmodule