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

////                                                              ////

////  OR1200's generate PC                                        ////

////                                                              ////

////  This file is part of the OpenRISC 1200 project              ////

////  http://www.opencores.org/project,or1k                       ////

////                                                              ////

////  Description                                                 ////

////  PC, interface to IC.                                        ////

////                                                              ////

////  To Do:                                                      ////

////   - make it smaller and faster                               ////

////                                                              ////

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

////      - Damjan Lampret, lampret@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                     ////

////                                                              ////

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

//

// $Log: or1200_genpc.v,v $

// Revision 2.0  2010/06/30 11:00:00  ORSoC

// Major update: 

// Structure reordered and bugs fixed. 

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`include "or1200_defines.v"

module or1200_genpc(

        // Clock and reset

        clk, rst,

        // External i/f to IC

        icpu_adr_o, icpu_cycstb_o, icpu_sel_o, icpu_tag_o,

        icpu_rty_i, icpu_adr_i,

        // Internal i/f

        pre_branch_op, branch_op, except_type, except_prefix,

        id_branch_addrtarget, ex_branch_addrtarget, muxed_b, operand_b,

        flag, flagforw, ex_branch_taken, except_start,

        epcr, spr_dat_i, spr_pc_we, genpc_refetch,

        genpc_freeze, no_more_dslot

);

//

// I/O

//

//

// Clock and reset

//

input                           clk;

input                           rst;

//

// External i/f to IC

//

output  [31:0]                   icpu_adr_o;

output                          icpu_cycstb_o;

output  [3:0]                    icpu_sel_o;

output  [3:0]                    icpu_tag_o;

input                           icpu_rty_i;

input   [31:0]                   icpu_adr_i;

//

// Internal i/f

//

input   [`OR1200_BRANCHOP_WIDTH-1:0]    pre_branch_op;

input   [`OR1200_BRANCHOP_WIDTH-1:0]     branch_op;

input   [`OR1200_EXCEPT_WIDTH-1:0]       except_type;

input                                   except_prefix;

input   [31:2]                  id_branch_addrtarget;

input   [31:2]                  ex_branch_addrtarget;

input   [31:0]                   muxed_b;

input   [31:0]                   operand_b;

input                           flag;

input                           flagforw;

output                          ex_branch_taken;

input                           except_start;

input   [31:0]                   epcr;

input   [31:0]                   spr_dat_i;

input                           spr_pc_we;

input                           genpc_refetch;

input                           genpc_freeze;

input                           no_more_dslot;

parameter boot_adr = `OR1200_BOOT_ADR;

//

// Internal wires and regs

//

reg     [31:2]                  pcreg_default;

reg                             pcreg_select;

reg     [31:2]                  pcreg;

reg     [31:0]                   pc;

// Set in event of jump or taken branch   

reg                             ex_branch_taken;

reg                             genpc_refetch_r;

   //

   // Address of insn to be fecthed

   //

   assign icpu_adr_o = !no_more_dslot & !except_start & !spr_pc_we

                       & (icpu_rty_i | genpc_refetch) ?

                       icpu_adr_i : {pc[31:2], 1'b0, ex_branch_taken|spr_pc_we};

   //

   // Control access to IC subsystem

   //

   assign icpu_cycstb_o = ~(genpc_freeze | (|pre_branch_op && !icpu_rty_i));

   assign icpu_sel_o = 4'b1111;

   assign icpu_tag_o = `OR1200_ITAG_NI;

   //

   // genpc_freeze_r

   //

   always @(posedge clk or `OR1200_RST_EVENT rst)

     if (rst == `OR1200_RST_VALUE)

       genpc_refetch_r <=  1'b0;

     else if (genpc_refetch)

       genpc_refetch_r <=  1'b1;

     else

       genpc_refetch_r <=  1'b0;

   //

   // Async calculation of new PC value. This value is used for addressing the

   // IC.

   //

   always @(pcreg or ex_branch_addrtarget or flag or branch_op or except_type

            or except_start or operand_b or epcr or spr_pc_we or spr_dat_i or

            except_prefix)

     begin

        casez ({spr_pc_we, except_start, branch_op}) // synopsys parallel_case

          {2'b00, `OR1200_BRANCHOP_NOP}: begin

             pc = {pcreg + 30'd1, 2'b0};

             ex_branch_taken = 1'b0;

          end

          {2'b00, `OR1200_BRANCHOP_J}: begin

`ifdef OR1200_VERBOSE

             // synopsys translate_off

             $display("%t: BRANCHOP_J: pc <= ex_branch_addrtarget %h"

                      , $time, ex_branch_addrtarget);

             // synopsys translate_on

`endif

             pc = {ex_branch_addrtarget, 2'b00};

             ex_branch_taken = 1'b1;

          end

          {2'b00, `OR1200_BRANCHOP_JR}: begin

`ifdef OR1200_VERBOSE

             // synopsys translate_off

             $display("%t: BRANCHOP_JR: pc <= operand_b %h",

                      $time, operand_b);

             // synopsys translate_on

`endif

             pc = operand_b;

             ex_branch_taken = 1'b1;

          end

          {2'b00, `OR1200_BRANCHOP_BF}:

            if (flag) begin

`ifdef OR1200_VERBOSE

               // synopsys translate_off

               $display("%t: BRANCHOP_BF: pc <= ex_branch_addrtarget %h",

                        $time, ex_branch_addrtarget);

               // synopsys translate_on

`endif

               pc = {ex_branch_addrtarget, 2'b00};

               ex_branch_taken = 1'b1;

            end

            else begin

`ifdef OR1200_VERBOSE

               // synopsys translate_off

               $display("%t: BRANCHOP_BF: not taken", $time);

               // synopsys translate_on

`endif

               pc = {pcreg + 30'd1, 2'b0};

               ex_branch_taken = 1'b0;

            end

          {2'b00, `OR1200_BRANCHOP_BNF}:

            if (flag) begin

`ifdef OR1200_VERBOSE

               // synopsys translate_off

               $display("%t: BRANCHOP_BNF: not taken", $time);

               // synopsys translate_on

`endif

               pc = {pcreg + 30'd1, 2'b0};

               ex_branch_taken = 1'b0;

            end

            else begin

`ifdef OR1200_VERBOSE

               // synopsys translate_off

               $display("%t: BRANCHOP_BNF: pc <= ex_branch_addrtarget %h",

                        $time, ex_branch_addrtarget);

               // synopsys translate_on

`endif

               pc = {ex_branch_addrtarget, 2'b00};

               ex_branch_taken = 1'b1;

            end

          {2'b00, `OR1200_BRANCHOP_RFE}: begin

`ifdef OR1200_VERBOSE

             // synopsys translate_off

             $display("%t: BRANCHOP_RFE: pc <= epcr %h",

                      $time, epcr);

             // synopsys translate_on

`endif

             pc = epcr;

             ex_branch_taken = 1'b1;

          end

          {2'b01, 3'b???}: begin

`ifdef OR1200_VERBOSE

             // synopsys translate_off

             $display("Starting exception: %h.", except_type);

             // synopsys translate_on

`endif

             pc = {(except_prefix ?

                    `OR1200_EXCEPT_EPH1_P : `OR1200_EXCEPT_EPH0_P),

                   except_type, `OR1200_EXCEPT_V};

             ex_branch_taken = 1'b1;

          end

          default: begin

`ifdef OR1200_VERBOSE

             // synopsys translate_off

             $display("l.mtspr writing into PC: %h.", spr_dat_i);

             // synopsys translate_on

`endif

             pc = spr_dat_i;

             ex_branch_taken = 1'b0;

          end

        endcase

     end

   //

   // PC register

   //

   always @(posedge clk or `OR1200_RST_EVENT rst)

     // default value 

     if (rst == `OR1200_RST_VALUE) begin

        pcreg_default <=  (boot_adr >>2) - 4;

        pcreg_select <=  1'b1;// select async. value due to reset state

     end

   // selected value (different from default) is written into FF after

   // reset state

     else if (pcreg_select) begin

        // dynamic value can only be assigned to FF out of reset! 

        pcreg_default <=  pcreg_boot[31:2];

        pcreg_select <=  1'b0;          // select FF value 

     end

     else if (spr_pc_we) begin

        pcreg_default <=  spr_dat_i[31:2];

     end

     else if (no_more_dslot | except_start | !genpc_freeze & !icpu_rty_i

              & !genpc_refetch) begin

        pcreg_default <=  pc[31:2];

     end

   // select async. value for pcreg after reset - PC jumps to the address selected

   // after boot.

   wire [31:0] pcreg_boot = boot_adr;

   always @(pcreg_boot or pcreg_default or pcreg_select)

     if (pcreg_select)

       // async. value is selected due to reset state 

       pcreg = pcreg_boot[31:2];

     else

       // FF value is selected 2nd clock after reset state 

       pcreg = pcreg_default ;

endmodule