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

////                                                              ////

////  8051 stack pointer                                          ////

////                                                              ////

////  This file is part of the 8051 cores project                 ////

////  http://www.opencores.org/cores/8051/                        ////

////                                                              ////

////  Description                                                 ////

////   8051 special function register: stack pointer.             ////

////                                                              ////

////  To Do:                                                      ////

////   nothing                                                    ////

////                                                              ////

////  Author(s):                                                  ////

////      - Simon Teran, simont@opencores.org                     ////

////                                                              ////

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

////                                                              ////

//// Copyright (C) 2000 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                     ////

////                                                              ////

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

//

// ver: 1

//

// synopsys translate_off

`include "oc8051_timescale.v"

// synopsys translate_on

`include "oc8051_defines.v"

module oc8051_sp (clk, rst, ram_rd_sel, ram_wr_sel, wr_addr, wr, wr_bit, data_in, data_out);

//

// clk          (in)  clock

// rst          (in)  reset

// ram_rd_sel   (in)  ram read select, used tu calculate next value [oc8051_decoder.ram_rd_sel]

// ram_wr_sel   (in)  ram write select, used tu calculate next value [oc8051_decoder.ram_wr_sel -r]

// wr           (in)  write [oc8051_decoder.wr -r]

// wr_bit       (in)  write bit addresable [oc8051_decoder.bit_addr -r]

// data_in      (in)  data input [oc8051_alu.des1]

// wr_addr      (in)  write address (if is addres of sp and white high must be written to sp)  [oc8051_ram_wr_sel.out]

// data_out     (out) data output [oc8051_ram_rd_sel.sp, oc8051_ram_rd_sel oc8051_ram_wr_sel1.sp, oc8051_ram_sel.sp]

//

input clk, rst, wr, wr_bit;

input [1:0] ram_rd_sel;

input [2:0] ram_wr_sel;

input [7:0] data_in, wr_addr;

output [7:0] data_out;

reg [7:0] data_out;

reg [7:0] temp;

reg pop, write;

wire [7:0] temp1;

assign temp1 = write ? data_in : temp;

always @(wr_addr or wr or wr_bit)

begin

  if ((wr_addr==`OC8051_SFR_SP) & (wr) & !(wr_bit))

    write = 1'b1;

  else

    write = 1'b0;

end

always @(posedge clk or posedge rst)

begin

  if (rst)

    temp <= #1 `OC8051_RST_SP;

  else

    temp <= #1 data_out;

end

always @(temp1 or ram_wr_sel or pop or write)

begin

//

// push

  if (ram_wr_sel==`OC8051_RWS_SP) data_out = temp1+8'h01;

  else if (write)

    data_out = temp1;

  else data_out = temp1 - pop;

end

always @(posedge clk or posedge rst)

begin

  if (rst)

    pop <= #1 1'b0;

  else if (ram_rd_sel==`OC8051_RRS_SP) pop <= #1 1'b1;

  else pop <= #1 1'b0;

end

endmodule