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

////                                                              ////

////  8051 memory interface                                       ////

////                                                              ////

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

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

////                                                              ////

////  Description                                                 ////

////   comunication betwen cpu and memory                         ////

////                                                              ////

////  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                     ////

////                                                              ////

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

//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

// Revision 1.8  2003/05/12 16:27:40  simont

// fix bug in movc intruction.

//

// Revision 1.7  2003/05/06 09:39:34  simont

// cahnge assigment to pc_wait (remove istb_o)

//

// Revision 1.6  2003/05/05 15:46:37  simont

// add aditional alu destination to solve critical path.

//

// Revision 1.5  2003/04/25 17:15:51  simont

// change branch instruction execution (reduse needed clock periods).

//

// Revision 1.4  2003/04/16 10:04:09  simont

// chance idat_ir to 24 bit wide

//

// Revision 1.3  2003/04/11 10:05:08  simont

// Change pc add value from 23'h to 16'h

//

// Revision 1.2  2003/04/09 16:24:03  simont

// change wr_sft to 2 bit wire.

//

// Revision 1.1  2003/01/13 14:13:12  simont

// initial import

//

//

// synopsys translate_off

`include "oc8051_timescale.v"

// synopsys translate_on

`include "oc8051_defines.v"

module oc8051_memory_interface (clk, rst,

//decoder

     wr_i,

     wr_bit_i,

     rd_sel,

     wr_sel,

     pc_wr_sel,

     pc_wr,

     pc,

     rd,

     mem_wait,

     mem_act,

     istb,

//internal ram

     wr_o,

     wr_bit_o,

     rd_addr,

     wr_addr,

     rd_ind,

     wr_ind,

     wr_dat,

     bit_in,

     in_ram,

     sfr,

     sfr_bit,

     bit_out,

     iram_out,

//program rom

     iadr_o,

     ea,

     ea_int,

     op1_out,

     op2_out,

     op3_out,

//internal

     idat_onchip,

//external

     iack_i,

     istb_o,

     idat_i,

//external data ram

     dadr_o,

     dwe_o,

     dstb_o,

     dack_i,

     ddat_i,

     ddat_o,

//interrupt interface

     intr,

     int_v,

     int_ack,

//alu

     des_acc,

     des1,

     des2,

//sfr's

     dptr,

     ri,

     sp,

     sp_w,

     rn,

     acc,

     reti

   );

input         clk,

              rst,

              wr_i,

              wr_bit_i;

input         bit_in,

              sfr_bit,

              dack_i;

input [2:0]   mem_act;

input [7:0]   in_ram,

              sfr,

              acc,

              sp_w;

input [31:0]  idat_i;

output        bit_out,

              mem_wait,

              reti;

output [7:0]  iram_out,

              wr_dat;

reg           bit_out,

              reti;

reg [7:0]     iram_out,

              sp_r;

reg           rd_addr_r;

output        wr_o,

              wr_bit_o;

//????

reg           dack_ir;

reg [7:0]     ddat_ir;

reg [23:0]    idat_ir;

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

//

//  rom_addr_sel

//

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

input         iack_i;

input [7:0]   des_acc,

              des1,

              des2;

output [15:0] iadr_o;

wire          ea_rom_sel;

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

//

// ext_addr_sel

//

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

input [7:0]   ri,

              ddat_i;

input [15:0]  dptr;

output        dstb_o,

              dwe_o;

output [7:0]  ddat_o;

output [15:0] dadr_o;

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

//

// ram_adr_sel

//

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

input [2:0]   rd_sel,

              wr_sel;

input [4:0]   rn;

input [7:0]   sp;

output        rd_ind,

              wr_ind;

output [7:0]  wr_addr,

              rd_addr;

reg           rd_ind,

              wr_ind;

reg [7:0]     wr_addr,

              rd_addr;

reg [4:0]     rn_r;

reg [7:0]     ri_r,

              imm_r,

              imm2_r,

              op1_r;

wire [7:0]    imm,

              imm2;

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

//

// op_select

//

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

input         intr,

              rd,

              ea,

              ea_int,

              istb;

input  [7:0]  int_v;

input  [31:0] idat_onchip;

output        int_ack,

              istb_o;

output  [7:0] op1_out,

              op3_out,

              op2_out;

reg           int_ack_t,

              int_ack,

              int_ack_buff;

reg [7:0]     int_vec_buff;

reg [7:0]     op1_out,

              op2_buff,

              op3_buff;

reg [7:0]     op1_o,

              op2_o,

              op3_o;

reg [7:0]     op1_xt,

              op2_xt,

              op3_xt;

reg [7:0]     op1,

              op2,

              op3;

wire [7:0]    op2_direct;

input [2:0]   pc_wr_sel;

input         pc_wr;

output [15:0] pc;

reg [15:0]    pc;

//

//pc            program counter register, save current value

reg [15:0]    pc_buf;

wire [15:0]   alu;

reg           int_buff,

              int_buff1; // interrupt buffer: used to prevent interrupting in the middle of executin instructions

//

//

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

reg           istb_t,

              imem_wait,

              dstb_o,

              dwe_o;

reg [7:0]     ddat_o;

reg [15:0]    iadr_t,

              dadr_ot;

reg           dmem_wait;

wire          pc_wait;

wire [1:0]    bank;

wire [7:0]    isr_call;

reg [1:0]     op_length;

reg [2:0]     op_pos;

wire          inc_pc;

reg           pc_wr_r;

wire [15:0]   pc_out;

reg [31:0]    idat_cur,

              idat_old;

reg           inc_pc_r,

              pc_wr_r2;

reg [7:0]     cdata;

reg           cdone;

assign bank       = rn[4:3];

assign imm        = op2_out;

assign imm2       = op3_out;

assign alu        = {des2, des_acc};

assign ea_rom_sel = ea && ea_int;

assign wr_o       = wr_i;

assign wr_bit_o   = wr_bit_i;

//assign mem_wait   = dmem_wait || imem_wait || pc_wr_r;

assign mem_wait   = dmem_wait || imem_wait || pc_wr_r2;

//assign mem_wait   = dmem_wait || imem_wait;

assign istb_o     = (istb || (istb_t & !iack_i)) && !dstb_o && !ea_rom_sel;

assign pc_wait    = rd && (ea_rom_sel || (!istb_t && iack_i));

assign wr_dat     = des1;

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

//

//  ram_select

//

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

always @(rd_addr_r or in_ram or sfr or bit_in or sfr_bit or rd_ind)

begin

  if (rd_addr_r && !rd_ind) begin

    iram_out = sfr;

    bit_out = sfr_bit;

  end else begin

    iram_out = in_ram;

    bit_out = bit_in;

  end

end

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

//

// ram_adr_sel

//

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

always @(rd_sel or sp or ri or rn or imm or dadr_o[15:0] or bank)

begin

  case (rd_sel)

    `OC8051_RRS_RN   : rd_addr = {3'h0, rn};

    `OC8051_RRS_I    : rd_addr = ri;

    `OC8051_RRS_D    : rd_addr = imm;

    `OC8051_RRS_SP   : rd_addr = sp;

    `OC8051_RRS_B    : rd_addr = `OC8051_SFR_B;

    `OC8051_RRS_DPTR : rd_addr = `OC8051_SFR_DPTR_LO;

    `OC8051_RRS_PSW  : rd_addr = `OC8051_SFR_PSW;

    `OC8051_RRS_ACC  : rd_addr = `OC8051_SFR_ACC;

    default          : rd_addr = 2'bxx;

  endcase

end

//

//

always @(wr_sel or sp_w or rn_r or imm_r or ri_r or imm2_r or op1_r or dadr_o[15:0])

begin

  case (wr_sel)

    `OC8051_RWS_RN : wr_addr = {3'h0, rn_r};

    `OC8051_RWS_I  : wr_addr = ri_r;

    `OC8051_RWS_D  : wr_addr = imm_r;

    `OC8051_RWS_SP : wr_addr = sp_w;

    `OC8051_RWS_D3 : wr_addr = imm2_r;

    `OC8051_RWS_B  : wr_addr = `OC8051_SFR_B;

    default        : wr_addr = 2'bxx;

  endcase

end

always @(posedge clk or posedge rst)

  if (rst)

    rd_ind <= #1 1'b0;

  else if ((rd_sel==`OC8051_RRS_I) || (rd_sel==`OC8051_RRS_SP))

    rd_ind <= #1 1'b1;

  else

    rd_ind <= #1 1'b0;

always @(wr_sel)

  if ((wr_sel==`OC8051_RWS_I) || (wr_sel==`OC8051_RWS_SP))

    wr_ind = 1'b1;

  else

    wr_ind = 1'b0;

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

//

//  rom_addr_sel

//

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

//

// output address is alu destination

// (instructions MOVC)

//assign iadr_o = (istb_t & !iack_i) ? iadr_t : pc_out;

assign iadr_o = (istb_t) ? iadr_t : pc_out;

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    iadr_t <= #1 23'h0;

    istb_t <= #1 1'b0;

    imem_wait <= #1 1'b0;

    idat_ir <= #1 24'h0;

  end else if (mem_act==`OC8051_MAS_CODE) begin

    iadr_t <= #1 alu;

    istb_t <= #1 1'b1;

    imem_wait <= #1 1'b1;

  end else if (ea_rom_sel && imem_wait) begin

    imem_wait <= #1 1'b0;

  end else if (!imem_wait && istb_t) begin

    istb_t <= #1 1'b0;

  end else if (iack_i) begin

    imem_wait <= #1 1'b0;

    idat_ir <= #1 idat_i [23:0];

  end

end

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

//

// ext_addr_sel

//

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

assign dadr_o = dadr_ot;

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    dwe_o <= #1 1'b0;

    dmem_wait <= #1 1'b0;

    dstb_o <= #1 1'b0;

    ddat_o <= #1 8'h00;

    dadr_ot <= #1 23'h0;

  end else if (dack_i) begin

    dwe_o <= #1 1'b0;

    dstb_o <= #1 1'b0;

    dmem_wait <= #1 1'b0;

  end else begin

    case (mem_act)

      `OC8051_MAS_DPTR_R: begin  // read from external rom: acc=(dptr)

        dwe_o <= #1 1'b0;

        dstb_o <= #1 1'b1;

        ddat_o <= #1 8'h00;

        dadr_ot <= #1 {7'h0, dptr};

        dmem_wait <= #1 1'b1;

      end

      `OC8051_MAS_DPTR_W: begin  // write to external rom: (dptr)=acc

        dwe_o <= #1 1'b1;

        dstb_o <= #1 1'b1;

        ddat_o <= #1 acc;

        dadr_ot <= #1 {7'h0, dptr};

        dmem_wait <= #1 1'b1;

      end

      `OC8051_MAS_RI_R:   begin  // read from external rom: acc=(Ri)

        dwe_o <= #1 1'b0;

        dstb_o <= #1 1'b1;

        ddat_o <= #1 8'h00;

        dadr_ot <= #1 {15'h0, ri};

        dmem_wait <= #1 1'b1;

      end

      `OC8051_MAS_RI_W: begin    // write to external rom: (Ri)=acc

        dwe_o <= #1 1'b1;

        dstb_o <= #1 1'b1;

        ddat_o <= #1 acc;

        dadr_ot <= #1 {15'h0, ri};

        dmem_wait <= #1 1'b1;

      end

    endcase

  end

end

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

//

// op_select

//

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

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    idat_cur <= #1 32'h0;

    idat_old <= #1 32'h0;

  end else if ((iack_i | ea_rom_sel) & (inc_pc | pc_wr_r2)) begin

    idat_cur <= #1 ea_rom_sel ? idat_onchip : idat_i;

    idat_old <= #1 idat_cur;

  end

end

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    cdata <= #1 8'h00;

    cdone <= #1 1'b0;

  end else if (istb_t) begin

    cdata <= #1 ea_rom_sel ? idat_onchip[7:0] : idat_i[7:0];

    cdone <= #1 1'b1;

  end else begin

    cdone <= #1 1'b0;

  end

end

always @(op_pos or idat_cur or idat_old)

begin

  case (op_pos)

    3'b000: begin

       op1 = idat_old[7:0]  ;

       op2 = idat_old[15:8] ;

       op3 = idat_old[23:16];

      end

    3'b001: begin

       op1 = idat_old[15:8] ;

       op2 = idat_old[23:16];

       op3 = idat_old[31:24];

      end

    3'b010: begin

       op1 = idat_old[23:16];

       op2 = idat_old[31:24];

       op3 = idat_cur[7:0]  ;

      end

    3'b011: begin

       op1 = idat_old[31:24];

       op2 = idat_cur[7:0]  ;

       op3 = idat_cur[15:8] ;

      end

    3'b100: begin

       op1 = idat_cur[7:0]  ;

       op2 = idat_cur[15:8] ;

       op3 = idat_cur[23:16];

      end

    default: begin

       op1 = idat_cur[15:8] ;

       op2 = idat_cur[23:16];

       op3 = idat_cur[31:24];

      end

  endcase

end

/*assign op1 = ea_rom_sel ? idat_onchip[7:0]   : op1_xt;

assign op2 = ea_rom_sel ? idat_onchip[15:8]  : op2_xt;

assign op3 = ea_rom_sel ? idat_onchip[23:16] : op3_xt;*/

always @(dack_ir or ddat_ir or op1_o or iram_out or cdone or cdata)

  if (dack_ir)

    op1_out = ddat_ir;

  else if (cdone)

    op1_out = cdata;

  else

    op1_out = op1_o;

assign op3_out = (rd) ? op3_o : op3_buff;

assign op2_out = (rd) ? op2_o : op2_buff;

always @(idat_i or iack_i or idat_ir or rd)

begin

  if (iack_i) begin

    op1_xt = idat_i[7:0];

    op2_xt = idat_i[15:8];

    op3_xt = idat_i[23:16];

  end else if (!rd) begin

    op1_xt = idat_ir[7:0];

    op2_xt = idat_ir[15:8];

    op3_xt = idat_ir[23:16];

  end else begin

    op1_xt = 8'h00;

    op2_xt = 8'h00;

    op3_xt = 8'h00;

  end

end

//

// in case of interrupts

always @(op1 or op2 or op3 or int_ack_t or int_vec_buff or iack_i or ea_rom_sel)

begin

  if (int_ack_t && (iack_i || ea_rom_sel)) begin

    op1_o = `OC8051_LCALL;

    op2_o = 8'h00;

    op3_o = int_vec_buff;

  end else begin

    op1_o = op1;

    op2_o = op2;

    op3_o = op3;

  end

end

//

//in case of reti

always @(posedge clk or posedge rst)

  if (rst) reti <= #1 1'b0;

  else if ((op1_o==`OC8051_RETI) & rd & !mem_wait) reti <= #1 1'b1;

  else reti <= #1 1'b0;

//

// remember inputs

always @(posedge clk or posedge rst)

begin

  if (rst) begin

    op2_buff <= #1 8'h0;

    op3_buff <= #1 8'h0;

  end else if (rd) begin

    op2_buff <= #1 op2_o;

    op3_buff <= #1 op3_o;

  end

end

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

//

//  pc

//

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

always @(op1_out)

begin

        casex (op1_out)

          `OC8051_ACALL :  op_length = 2'h2;

          `OC8051_AJMP :   op_length = 2'h2;

        //op_code [7:3]

          `OC8051_CJNE_R : op_length = 2'h3;

          `OC8051_DJNZ_R : op_length = 2'h2;

          `OC8051_MOV_DR : op_length = 2'h2;