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//////////////////////////////////////////////////////////////////////
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////                                                              ////
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////  OR1200's generate PC                                        ////
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////                                                              ////
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////  This file is part of the OpenRISC 1200 project              ////
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////  http://www.opencores.org/project,or1k                       ////
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////                                                              ////
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////  Description                                                 ////
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////  PC, interface to IC.                                        ////
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////                                                              ////
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////  To Do:                                                      ////
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////   - make it smaller and faster                               ////
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////                                                              ////
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////  Author(s):                                                  ////
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////      - Damjan Lampret, lampret@opencores.org                 ////
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////                                                              ////
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//////////////////////////////////////////////////////////////////////
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////                                                              ////
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//// Copyright (C) 2000 Authors and OPENCORES.ORG                 ////
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////                                                              ////
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//// This source file may be used and distributed without         ////
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//// restriction provided that this copyright statement is not    ////
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//// removed from the file and that any derivative work contains  ////
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//// the original copyright notice and the associated disclaimer. ////
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////                                                              ////
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//// This source file is free software; you can redistribute it   ////
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//// and/or modify it under the terms of the GNU Lesser General   ////
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//// Public License as published by the Free Software Foundation; ////
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//// either version 2.1 of the License, or (at your option) any   ////
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//// later version.                                               ////
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////                                                              ////
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//// This source is distributed in the hope that it will be       ////
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//// useful, but WITHOUT ANY WARRANTY; without even the implied   ////
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//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ////
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//// PURPOSE.  See the GNU Lesser General Public License for more ////
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//// details.                                                     ////
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////                                                              ////
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//// You should have received a copy of the GNU Lesser General    ////
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//// Public License along with this source; if not, download it   ////
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//// from http://www.opencores.org/lgpl.shtml                     ////
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////                                                              ////
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//////////////////////////////////////////////////////////////////////
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//
44 141 marcus.erl
// $Log: or1200_genpc.v,v $
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// Revision 2.0  2010/06/30 11:00:00  ORSoC
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// Major update: 
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// Structure reordered and bugs fixed. 
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// synopsys translate_off
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`include "timescale.v"
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// synopsys translate_on
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`include "or1200_defines.v"
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module or1200_genpc(
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        // Clock and reset
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        clk, rst,
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        // External i/f to IC
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        icpu_adr_o, icpu_cycstb_o, icpu_sel_o, icpu_tag_o,
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        icpu_rty_i, icpu_adr_i,
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        // Internal i/f
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        pre_branch_op, branch_op, except_type, except_prefix,
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        id_branch_addrtarget, ex_branch_addrtarget, muxed_b, operand_b,
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        flag, flagforw, ex_branch_taken, except_start,
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        epcr, spr_dat_i, spr_pc_we, genpc_refetch,
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        genpc_freeze, no_more_dslot
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);
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//
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// I/O
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//
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//
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// Clock and reset
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//
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input                           clk;
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input                           rst;
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//
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// External i/f to IC
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//
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output  [31:0]                   icpu_adr_o;
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output                          icpu_cycstb_o;
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output  [3:0]                    icpu_sel_o;
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output  [3:0]                    icpu_tag_o;
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input                           icpu_rty_i;
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input   [31:0]                   icpu_adr_i;
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//
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// Internal i/f
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//
93 141 marcus.erl
input   [`OR1200_BRANCHOP_WIDTH-1:0]    pre_branch_op;
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input   [`OR1200_BRANCHOP_WIDTH-1:0]     branch_op;
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input   [`OR1200_EXCEPT_WIDTH-1:0]       except_type;
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input                                   except_prefix;
97 141 marcus.erl
input   [31:2]                  id_branch_addrtarget;
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input   [31:2]                  ex_branch_addrtarget;
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input   [31:0]                   muxed_b;
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input   [31:0]                   operand_b;
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input                           flag;
102 141 marcus.erl
input                           flagforw;
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output                          ex_branch_taken;
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input                           except_start;
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input   [31:0]                   epcr;
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input   [31:0]                   spr_dat_i;
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input                           spr_pc_we;
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input                           genpc_refetch;
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input                           genpc_freeze;
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input                           no_more_dslot;
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//
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// Internal wires and regs
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//
115 141 marcus.erl
reg     [31:2]                  pcreg_default;
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wire    [31:0]                   pcreg_boot;
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reg                             pcreg_select;
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reg     [31:2]                  pcreg;
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reg     [31:0]                   pc;
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// Set in event of jump or taken branch   
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reg                             ex_branch_taken;
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reg                             genpc_refetch_r;
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124 186 julius
   //
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   // Address of insn to be fecthed
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   //
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   assign icpu_adr_o = !no_more_dslot & !except_start & !spr_pc_we
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                       & (icpu_rty_i | genpc_refetch) ?
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                       icpu_adr_i : {pc[31:2], 1'b0, ex_branch_taken|spr_pc_we};
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131 186 julius
   //
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   // Control access to IC subsystem
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   //
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   assign icpu_cycstb_o = ~(genpc_freeze | (|pre_branch_op && !icpu_rty_i));
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   assign icpu_sel_o = 4'b1111;
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   assign icpu_tag_o = `OR1200_ITAG_NI;
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138 186 julius
   //
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   // genpc_freeze_r
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   //
141 358 julius
   always @(posedge clk or `OR1200_RST_EVENT rst)
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     if (rst == `OR1200_RST_VALUE)
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       genpc_refetch_r <=  1'b0;
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     else if (genpc_refetch)
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       genpc_refetch_r <=  1'b1;
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     else
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       genpc_refetch_r <=  1'b0;
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149 186 julius
   //
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   // Async calculation of new PC value. This value is used for addressing the
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   // IC.
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   //
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   always @(pcreg or ex_branch_addrtarget or flag or branch_op or except_type
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            or except_start or operand_b or epcr or spr_pc_we or spr_dat_i or
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            except_prefix)
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     begin
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        casez ({spr_pc_we, except_start, branch_op}) // synopsys parallel_case
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          {2'b00, `OR1200_BRANCHOP_NOP}: begin
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             pc = {pcreg + 30'd1, 2'b0};
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             ex_branch_taken = 1'b0;
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          end
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          {2'b00, `OR1200_BRANCHOP_J}: begin
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`ifdef OR1200_VERBOSE
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             // synopsys translate_off
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             $display("%t: BRANCHOP_J: pc <= ex_branch_addrtarget %h"
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                      , $time, ex_branch_addrtarget);
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             // synopsys translate_on
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`endif
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             pc = {ex_branch_addrtarget, 2'b00};
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             ex_branch_taken = 1'b1;
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          end
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          {2'b00, `OR1200_BRANCHOP_JR}: begin
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`ifdef OR1200_VERBOSE
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             // synopsys translate_off
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             $display("%t: BRANCHOP_JR: pc <= operand_b %h",
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                      $time, operand_b);
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             // synopsys translate_on
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`endif
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             pc = operand_b;
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             ex_branch_taken = 1'b1;
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          end
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          {2'b00, `OR1200_BRANCHOP_BF}:
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            if (flag) begin
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`ifdef OR1200_VERBOSE
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               // synopsys translate_off
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               $display("%t: BRANCHOP_BF: pc <= ex_branch_addrtarget %h",
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                        $time, ex_branch_addrtarget);
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               // synopsys translate_on
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`endif
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               pc = {ex_branch_addrtarget, 2'b00};
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               ex_branch_taken = 1'b1;
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            end
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            else begin
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`ifdef OR1200_VERBOSE
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               // synopsys translate_off
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               $display("%t: BRANCHOP_BF: not taken", $time);
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               // synopsys translate_on
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`endif
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               pc = {pcreg + 30'd1, 2'b0};
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               ex_branch_taken = 1'b0;
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            end
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          {2'b00, `OR1200_BRANCHOP_BNF}:
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            if (flag) begin
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`ifdef OR1200_VERBOSE
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               // synopsys translate_off
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               $display("%t: BRANCHOP_BNF: not taken", $time);
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               // synopsys translate_on
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`endif
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               pc = {pcreg + 30'd1, 2'b0};
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               ex_branch_taken = 1'b0;
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            end
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            else begin
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`ifdef OR1200_VERBOSE
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               // synopsys translate_off
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               $display("%t: BRANCHOP_BNF: pc <= ex_branch_addrtarget %h",
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                        $time, ex_branch_addrtarget);
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               // synopsys translate_on
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`endif
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               pc = {ex_branch_addrtarget, 2'b00};
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               ex_branch_taken = 1'b1;
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            end
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          {2'b00, `OR1200_BRANCHOP_RFE}: begin
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`ifdef OR1200_VERBOSE
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             // synopsys translate_off
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             $display("%t: BRANCHOP_RFE: pc <= epcr %h",
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                      $time, epcr);
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             // synopsys translate_on
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`endif
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             pc = epcr;
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             ex_branch_taken = 1'b1;
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          end
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          {2'b01, 3'b???}: begin
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`ifdef OR1200_VERBOSE
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             // synopsys translate_off
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             $display("Starting exception: %h.", except_type);
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             // synopsys translate_on
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`endif
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             pc = {(except_prefix ?
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                    `OR1200_EXCEPT_EPH1_P : `OR1200_EXCEPT_EPH0_P),
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                   except_type, `OR1200_EXCEPT_V};
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             ex_branch_taken = 1'b1;
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          end
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          default: begin
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`ifdef OR1200_VERBOSE
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             // synopsys translate_off
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             $display("l.mtspr writing into PC: %h.", spr_dat_i);
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             // synopsys translate_on
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`endif
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             pc = spr_dat_i;
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             ex_branch_taken = 1'b0;
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          end
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        endcase
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     end
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255 186 julius
   //
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   // PC register
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   //
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   always @(posedge clk or `OR1200_RST_EVENT rst)
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     // default value 
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     if (rst == `OR1200_RST_VALUE) begin
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        pcreg_default <=  `OR1200_BOOT_PCREG_DEFAULT; // jb
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        pcreg_select <=  1'b1;// select async. value due to reset state
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     end
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   // selected value (different from default) is written into FF after
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   // reset state
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     else if (pcreg_select) begin
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        // dynamic value can only be assigned to FF out of reset! 
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        pcreg_default <=  pcreg_boot[31:2];
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        pcreg_select <=  1'b0;          // select FF value 
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     end
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     else if (spr_pc_we) begin
272 258 julius
        pcreg_default <=  spr_dat_i[31:2];
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     end
274
     else if (no_more_dslot | except_start | !genpc_freeze & !icpu_rty_i
275
              & !genpc_refetch) begin
276 258 julius
        pcreg_default <=  pc[31:2];
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     end
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279 186 julius
   // select async. value for pcreg after reset - PC jumps to the address selected
280
   // after boot.
281 141 marcus.erl
   assign  pcreg_boot = `OR1200_BOOT_ADR; // changed JB
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283 186 julius
   always @(pcreg_boot or pcreg_default or pcreg_select)
284
     if (pcreg_select)
285
       // async. value is selected due to reset state 
286
       pcreg = pcreg_boot[31:2];
287
     else
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       // FF value is selected 2nd clock after reset state 
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       pcreg = pcreg_default ;
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endmodule

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