Subversion Repositories oms8051mini

//////////////////////////////////////////////////////////////////////
////                                                              ////
////  8051 memory interface                                       ////
////                                                              ////
////  This file is part of the 8051 cores project                 ////
////  http://www.opencores.org/cores/oms8051mini/                 ////
////                                                              ////
////  Description                                                 ////
////   comunication betwen cpu and memory                         ////
////                                                              ////
////  To Do:                                                      ////
////   nothing                                                    ////
////                                                              ////
////  Author(s):                                                  ////
////      - Simon Teran, simont@opencores.org                     ////
////      - Dinesh Annayya, dinesha@opencores.org                 ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////   v0.0 - Dinesh A, 5th Jan 2017
////        1. Active edge of reset changed from High to Low
////   v0.1 - Dinesh A, 6th Jan 2017
////        1. pc_next logic added
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// 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 1.12  2003/07/01 20:47:39  simont
// add /* synopsys xx_case */ to case statments.
//
// Revision 1.11  2003/06/20 13:35:10  simont
// simualtion `ifdef added
//
// Revision 1.10  2003/06/05 11:15:02  simont
// fix bug.
//
// Revision 1.9  2003/06/03 17:09:57  simont
// pipelined acces to axternal instruction interface added.
//
// 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
//
//
 
 
`include "top_defines.v"
 
 
module oc8051_memory_interface (clk, resetn,
 
//decoder
     wr_i,
     wr_bit_i,
     rd_sel,
     wr_sel,
     pc_wr_sel,
     pc_wr,
     pc,
     pc_next,
     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,
              resetn,
	      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;
output [15:0] pc_next;
 
reg [15:0]    pc,pc_next;
 
//
//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;
 
 
`ifdef OC8051_SIMULATION
  always @(negedge resetn) begin
    #5
    if (ea_rom_sel)
      $display("   progran execution from external rom");
    else
      $display("   progran execution from internal rom");
  end
 
`endif
 
 
/////////////////////////////
//
//  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) /* synopsys full_case parallel_case */
    `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) /* synopsys full_case parallel_case */
    `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'b00;
  endcase
end
 
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0)
    rd_ind <= 1'b0;
  else if ((rd_sel==`OC8051_RRS_I) || (rd_sel==`OC8051_RRS_SP))
    rd_ind <= 1'b1;
  else
    rd_ind <= 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 negedge resetn)
begin
  if (resetn == 1'b0) begin
    iadr_t <= 23'h0;
    istb_t <= 1'b0;
    imem_wait <= 1'b0;
    idat_ir <= 24'h0;
  end else if (mem_act==`OC8051_MAS_CODE) begin
    iadr_t <= alu;
    istb_t <= 1'b1;
    imem_wait <= 1'b1;
  end else if (ea_rom_sel && imem_wait) begin
    imem_wait <= 1'b0;
  end else if (!imem_wait && istb_t) begin
    istb_t <= 1'b0;
  end else if (iack_i) begin
    imem_wait <= 1'b0;
    idat_ir <= idat_i [23:0];
  end
end
 
/////////////////////////////
//
// ext_addr_sel
//
/////////////////////////////
 
assign dadr_o = dadr_ot;
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0) begin
    dwe_o <= 1'b0;
    dmem_wait <= 1'b0;
    dstb_o <= 1'b0;
    ddat_o <= 8'h00;
    dadr_ot <= 23'h0;
  end else if (dack_i) begin
    dwe_o <= 1'b0;
    dstb_o <= 1'b0;
    dmem_wait <= 1'b0;
  end else begin
    case (mem_act) /* synopsys full_case parallel_case */
      `OC8051_MAS_DPTR_R: begin  // read from external rom: acc=(dptr)
        dwe_o <= 1'b0;
        dstb_o <= 1'b1;
        ddat_o <= 8'h00;
        dadr_ot <= {7'h0, dptr};
        dmem_wait <= 1'b1;
      end
      `OC8051_MAS_DPTR_W: begin  // write to external rom: (dptr)=acc
        dwe_o <= 1'b1;
        dstb_o <= 1'b1;
        ddat_o <= acc;
        dadr_ot <= {7'h0, dptr};
        dmem_wait <= 1'b1;
      end
      `OC8051_MAS_RI_R:   begin  // read from external rom: acc=(Ri)
        dwe_o <= 1'b0;
        dstb_o <= 1'b1;
        ddat_o <= 8'h00;
        dadr_ot <= {15'h0, ri};
        dmem_wait <= 1'b1;
      end
      `OC8051_MAS_RI_W: begin    // write to external rom: (Ri)=acc
        dwe_o <= 1'b1;
        dstb_o <= 1'b1;
        ddat_o <= acc;
        dadr_ot <= {15'h0, ri};
        dmem_wait <= 1'b1;
      end
    default: begin
       dwe_o <= dwe_o;
       dmem_wait <= dmem_wait;
       dstb_o <= dstb_o;
       ddat_o <= ddat_o;
       dadr_ot <= dadr_ot;
      end
    endcase
  end
end
 
/////////////////////////////
//
// op_select
//
/////////////////////////////
 
 
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0) begin
    idat_cur <= 32'h0;
    idat_old <= 32'h0;
  end else if ((iack_i | ea_rom_sel) & (inc_pc | pc_wr_r2)) begin
    idat_cur <= ea_rom_sel ? idat_onchip : idat_i;
    idat_old <= idat_cur;
  end
 
end
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0) begin
    cdata <= 8'h00;
    cdone <= 1'b0;
  end else if (istb_t) begin
    cdata <= ea_rom_sel ? idat_onchip[7:0] : idat_i[7:0];
    cdone <= 1'b1;
  end else begin
    cdone <= 1'b0;
  end
end
 
always @(op_pos or idat_cur or idat_old)
begin
  case (op_pos)  /* synopsys parallel_case */
    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
 
 
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 negedge resetn)
  if (resetn == 1'b0) reti <= 1'b0;
  else if ((op1_o==`OC8051_RETI) & rd & !mem_wait) reti <= 1'b1;
  else reti <= 1'b0;
 
//
// remember inputs
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0) begin
    op2_buff <= 8'h0;
    op3_buff <= 8'h0;
  end else if (rd) begin
    op2_buff <= op2_o;
    op3_buff <= op3_o;
  end
end
 
/////////////////////////////
//
//  pc
//
/////////////////////////////
 
always @(op1_out)
begin
        casex (op1_out) /* synopsys parallel_case */
          `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;
          `OC8051_MOV_CR : op_length = 2'h2;
          `OC8051_MOV_RD : op_length = 2'h2;
 
        //op_code [7:1]
          `OC8051_CJNE_I : op_length = 2'h3;
          `OC8051_MOV_ID : op_length = 2'h2;
          `OC8051_MOV_DI : op_length = 2'h2;
          `OC8051_MOV_CI : op_length = 2'h2;
 
        //op_code [7:0]
          `OC8051_ADD_D :  op_length = 2'h2;
          `OC8051_ADD_C :  op_length = 2'h2;
          `OC8051_ADDC_D : op_length = 2'h2;
          `OC8051_ADDC_C : op_length = 2'h2;
          `OC8051_ANL_D :  op_length = 2'h2;
          `OC8051_ANL_C :  op_length = 2'h2;
          `OC8051_ANL_DD : op_length = 2'h2;
          `OC8051_ANL_DC : op_length = 2'h3;
          `OC8051_ANL_B :  op_length = 2'h2;
          `OC8051_ANL_NB : op_length = 2'h2;
          `OC8051_CJNE_D : op_length = 2'h3;
          `OC8051_CJNE_C : op_length = 2'h3;
          `OC8051_CLR_B :  op_length = 2'h2;
          `OC8051_CPL_B :  op_length = 2'h2;
          `OC8051_DEC_D :  op_length = 2'h2;
          `OC8051_DJNZ_D : op_length = 2'h3;
          `OC8051_INC_D :  op_length = 2'h2;
          `OC8051_JB :     op_length = 2'h3;
          `OC8051_JBC :    op_length = 2'h3;
          `OC8051_JC :     op_length = 2'h2;
          `OC8051_JNB :    op_length = 2'h3;
          `OC8051_JNC :    op_length = 2'h2;
          `OC8051_JNZ :    op_length = 2'h2;
          `OC8051_JZ :     op_length = 2'h2;
          `OC8051_LCALL :  op_length = 2'h3;
          `OC8051_LJMP :   op_length = 2'h3;
          `OC8051_MOV_D :  op_length = 2'h2;
          `OC8051_MOV_C :  op_length = 2'h2;
          `OC8051_MOV_DA : op_length = 2'h2;
          `OC8051_MOV_DD : op_length = 2'h3;
          `OC8051_MOV_CD : op_length = 2'h3;
          `OC8051_MOV_BC : op_length = 2'h2;
          `OC8051_MOV_CB : op_length = 2'h2;
          `OC8051_MOV_DP : op_length = 2'h3;
          `OC8051_ORL_D :  op_length = 2'h2;
          `OC8051_ORL_C :  op_length = 2'h2;
          `OC8051_ORL_AD : op_length = 2'h2;
          `OC8051_ORL_CD : op_length = 2'h3;
          `OC8051_ORL_B :  op_length = 2'h2;
          `OC8051_ORL_NB : op_length = 2'h2;
          `OC8051_POP :    op_length = 2'h2;
          `OC8051_PUSH :   op_length = 2'h2;
          `OC8051_SETB_B : op_length = 2'h2;
          `OC8051_SJMP :   op_length = 2'h2;
          `OC8051_SUBB_D : op_length = 2'h2;
          `OC8051_SUBB_C : op_length = 2'h2;
          `OC8051_XCH_D :  op_length = 2'h2;
          `OC8051_XRL_D :  op_length = 2'h2;
          `OC8051_XRL_C :  op_length = 2'h2;
          `OC8051_XRL_AD : op_length = 2'h2;
          `OC8051_XRL_CD : op_length = 2'h3;
          default:         op_length = 2'h1;
        endcase
end
 
 
assign inc_pc = ((op_pos[2] | (&op_pos[1:0])) & rd) | pc_wr_r2;
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0) begin
    op_pos <= 3'h0;
  end else if (pc_wr_r2) begin
    op_pos <= 3'h4;// - op_length;////****??????????
  end else if (inc_pc & rd) begin
    op_pos[2]   <= op_pos[2] & !op_pos[1] & op_pos[0] & (&op_length);
    op_pos[1:0] <= op_pos[1:0] + op_length;
  end else if (rd) begin
    op_pos <= op_pos + {1'b0, op_length};
  end
end
 
//
// remember interrupt
// we don't want to interrupt instruction in the middle of execution
always @(posedge clk or negedge resetn)
 if (resetn == 1'b0) begin
   int_ack_t <= 1'b0;
   int_vec_buff <= 8'h00;
 end else if (intr) begin
   int_ack_t <= 1'b1;
   int_vec_buff <= int_v;
 end else if (rd && (ea_rom_sel || iack_i) && !pc_wr_r2) int_ack_t <= 1'b0;
 
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0) int_ack_buff <= 1'b0;
  else int_ack_buff <= int_ack_t;
 
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0) int_ack <= 1'b0;
  else begin
    if ((int_ack_buff) & !(int_ack_t))
      int_ack <= 1'b1;
    else int_ack <= 1'b0;
  end
 
 
//
//interrupt buffer
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0) begin
    int_buff1 <= 1'b0;
  end else begin
    int_buff1 <= int_buff;
  end
 
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0) begin
    int_buff <= 1'b0;
  end else if (intr) begin
    int_buff <= 1'b1;
  end else if (pc_wait)
    int_buff <= 1'b0;
 
wire [7:0]  pcs_source;
reg  [15:0] pcs_result;
reg         pcs_cy;
 
assign pcs_source = pc_wr_sel[0] ? op3_out : op2_out;
 
always @(pcs_source or pc or pcs_cy)
begin
  if (pcs_source[7]) begin
    {pcs_cy, pcs_result[7:0]} = {1'b0, pc[7:0]} + {1'b0, pcs_source};
    pcs_result[15:8] = pc[15:8] - {7'h0, !pcs_cy};
  end else pcs_result = pc + {8'h00, pcs_source};
end
 
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0)
    pc <= 16'h0;
  else if (pc_wr_r2)
    pc <= pc_buf;
  else if (rd && !int_ack_t && !(pc_wr && (pc_wr_sel != `OC8051_PIS_AH)) && !pc_wr_r)
    pc <= pc_buf - 16'h8 + {13'h0, op_pos} + {14'h0, op_length};
end
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0)
    pc_next <= 16'h0;
  else if (pc_wr_r2)
    pc_next <= pc_buf;
  else if (rd && !int_ack_t)
    pc_next <= pc_buf - 16'h8 + {13'h0, op_pos} + {14'h0, op_length};
end
 
always @(posedge clk or negedge resetn)
begin
  if (resetn == 1'b0) begin
    pc_buf <= `OC8051_RST_PC;
  end else if (pc_wr) begin
//
//case of writing new value to pc (jupms)
      case (pc_wr_sel) /* synopsys full_case parallel_case */
        `OC8051_PIS_ALU: pc_buf        <= alu;
        `OC8051_PIS_AL:  pc_buf[7:0]   <= alu[7:0];
        `OC8051_PIS_AH:  pc_buf[15:8]  <= alu[7:0];
        `OC8051_PIS_I11: pc_buf[10:0]  <= {op1_out[7:5], op2_out};
        `OC8051_PIS_I16: pc_buf        <= {op2_out, op3_out};
        `OC8051_PIS_SO1: pc_buf        <= pcs_result;
        `OC8051_PIS_SO2: pc_buf        <= pcs_result;
        default: pc_buf <= `OC8051_RST_PC;
      endcase
//  end else if (inc_pc) begin
  end else begin
//
//or just remember current
      pc_buf <= pc_out;
  end
end
 
 
assign pc_out = inc_pc ? pc_buf + 16'h4
                       : pc_buf ;
 
 
 
 
 
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0)
    ddat_ir <= 8'h00;
  else if (dack_i)
    ddat_ir <= ddat_i;
 
 
////////////////////////
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0) begin
    rn_r      <= 5'd0;
    ri_r      <= 8'h00;
    imm_r     <= 8'h00;
    imm2_r    <= 8'h00;
    rd_addr_r <= 1'b0;
    op1_r     <= 8'h0;
    dack_ir   <= 1'b0;
    sp_r      <= 1'b0;
    pc_wr_r   <= 1'b0;
    pc_wr_r2  <= 1'b0;
  end else begin
    rn_r      <= rn;
    ri_r      <= ri;
    imm_r     <= imm;
    imm2_r    <= imm2;
    rd_addr_r <= rd_addr[7];
    op1_r     <= op1_out;
    dack_ir   <= dack_i;
    sp_r      <= sp;
    pc_wr_r   <= pc_wr && (pc_wr_sel != `OC8051_PIS_AH);
    pc_wr_r2  <= pc_wr_r;
  end
 
always @(posedge clk or negedge resetn)
  if (resetn == 1'b0) begin
    inc_pc_r  <= 1'b1;
  end else if (istb) begin
    inc_pc_r  <= inc_pc;
  end
 
`ifdef OC8051_SIMULATION
 
initial
begin
  wait (!resetn)
  if (ea_rom_sel) begin
    $display(" ");
    $display("\t Program running from internal rom !");
    $display(" ");
  end else begin
    $display(" ");
    $display("\t Program running from external rom !");
    $display(" ");
  end
end
`endif
 
 
endmodule