//////////////////////////////////////////////////////////////////////
////                                                              ////
////  8051 core decoder                                           ////
////                                                              ////
////  This file is part of the 8051 cores project                 ////
////  http://www.opencores.org/cores/8051/                        ////
////                                                              ////
////  Description                                                 ////
////   Main 8051 core module. decodes instruction and creates     ////
////   control sigals.                                            ////
////                                                              ////
////  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_decoder (clk, rst, op_in, ram_rd_sel, ram_wr_sel, bit_addr, wr, src_sel1, src_sel2, src_sel3, alu_op, psw_set, cy_sel, imm_sel, pc_wr, pc_sel,
                comp_sel, eq, rom_addr_sel, ext_addr_sel, wad2, rd, write_x, reti);

// clk          clock
// rst          reset
// op_in        operation code
// ram_rd_sel   select, whitch address will be send to ram for read
// ram_wr_sel   select, whitch address will be send to ram for write
// wr           write - if 1 then we will write to ram
// src_sel1     select alu source 1
// src_sel2     select alu source 2
// src_sel3     select alu source 3
// alu_op       alu operation
// psw_set      will we remember cy, ac, ov from alu
// cy_sel       carry in alu select
// comp_sel     compare source select
// eq   compare result
// bit_addr     if instruction is bit addresable
// wad2         wrihe acc from destination 2
// imm_sel      immediate select
// pc_wr        pc write
// pc_sel       pc select
// rom_addr_sel rom address select (alu destination or pc)
// ext_addr_sel external address select (dptr or Ri)
// rd           read from rom
// write_x      write to external rom
// reti         return from interrupt


input clk, rst, eq;
input [7:0] op_in;

output wr, reti, write_x, bit_addr, src_sel3, rom_addr_sel, ext_addr_sel, pc_wr, wad2;
output [1:0] ram_rd_sel, src_sel1, src_sel2, psw_set, imm_sel, cy_sel, pc_sel;
output [2:0] ram_wr_sel, comp_sel;
output [3:0] alu_op;
output rd;

reg reti, write_x;
reg wr,  bit_addr, src_sel3, rom_addr_sel, ext_addr_sel, pc_wr, wad2;
reg [1:0] psw_set, ram_rd_sel, src_sel1, src_sel2, imm_sel, pc_sel, cy_sel;
reg [3:0] alu_op;
reg [2:0] comp_sel, ram_wr_sel;

//
// state        if 2'b00 then normal execution, sle instructin that need more than one clock
// op           instruction buffer
reg [1:0] state;
reg [7:0] op;

//
// if state = 2'b00 then read nex instruction
assign rd = !state[0] & !state[1];

//
// main block
// case of instruction set control signals
always @(rst or op_in or eq or state or op)
begin
  if (rst) begin
    ram_rd_sel = `OC8051_RRS_DC;
    ram_wr_sel = `OC8051_RWS_DC;
    src_sel1 = `OC8051_ASS_DC;
    src_sel2 = `OC8051_ASS_DC;
    alu_op = `OC8051_ALU_NOP;
    imm_sel = `OC8051_IDS_DC;
    wr = 1'b0;
    psw_set = `OC8051_PS_NOT;
    cy_sel = `OC8051_CY_0;
    pc_wr = `OC8051_PCW_N;
    pc_sel = `OC8051_PIS_DC;
    comp_sel = `OC8051_CSS_DC;
    bit_addr = 1'b0;
    src_sel3 = `OC8051_AS3_DC;
    rom_addr_sel = `OC8051_RAS_PC;
    ext_addr_sel = `OC8051_EAS_DC;
    wad2 = `OC8051_WAD_N;
  end else begin
    case (state)
      2'b01: begin
    casex (op)
      `OC8051_ACALL :begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_SP;
          src_sel1 = `OC8051_ASS_IMM;
          src_sel2 = 2'bxx;
          alu_op = `OC8051_ALU_NOP;
          imm_sel = `OC8051_IDS_PCH;
          wr = 1'b1;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = `OC8051_PCW_N;
          pc_sel = `OC8051_PIS_DC;
          comp_sel = `OC8051_CSS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DC;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_AJMP : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = 2'bxx;
          alu_op = `OC8051_ALU_NOP;
          imm_sel = `OC8051_IDS_DC;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = `OC8051_PCW_N;
          pc_sel = `OC8051_PIS_DC;
          comp_sel = `OC8051_CSS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DC;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_LCALL :begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_SP;
          src_sel1 = `OC8051_ASS_IMM;
          src_sel2 = 2'bxx;
          alu_op = `OC8051_ALU_NOP;
          imm_sel = `OC8051_IDS_PCH;
          wr = 1'b1;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = `OC8051_PCW_N;
          pc_sel = `OC8051_PIS_DC;
          comp_sel = `OC8051_CSS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DC;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      default begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = `OC8051_PCW_N;
          pc_sel = `OC8051_PIS_DC;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DC;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
      end
    endcase
    end
    2'b10:
    casex (op)
      `OC8051_CJNE_R : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = !eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DES;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_CJNE_I : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = !eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DES;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_CJNE_D : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = !eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DES;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_CJNE_C : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = !eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DES;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_DJNZ_R : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DES;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_DJNZ_D : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_DES;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_JB : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b0;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_BIT;
          bit_addr = 1'b0;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_JBC : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_D;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;
          wr = 1'b1;
          psw_set = `OC8051_PS_NOT;
          cy_sel = `OC8051_CY_0;
          pc_wr = eq;
          pc_sel = `OC8051_PIS_ALU;
          imm_sel = `OC8051_IDS_DC;
          src_sel3 = `OC8051_AS3_DC;
          comp_sel = `OC8051_CSS_BIT;
          bit_addr = 1'b1;
          wad2 = `OC8051_WAD_N;
          rom_addr_sel = `OC8051_RAS_PC;
          ext_addr_sel = `OC8051_EAS_DC;
        end
      `OC8051_JC : begin
          ram_rd_sel = `OC8051_RRS_DC;
          ram_wr_sel = `OC8051_RWS_DC;
          src_sel1 = `OC8051_ASS_DC;
          src_sel2 = `OC8051_ASS_DC;
          alu_op = `OC8051_ALU_NOP;