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

////                                                              ////

////  OR1200's Instruction decode                                 ////

////                                                              ////

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

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

////                                                              ////

////  Description                                                 ////

////  Majority of instruction decoding is performed here.         ////

////                                                              ////

////  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_ctrl.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_ctrl

  (

   // Clock and reset

   clk, rst,

   // Internal i/f

   except_flushpipe, extend_flush, if_flushpipe, id_flushpipe, ex_flushpipe,

   wb_flushpipe,

   id_freeze, ex_freeze, wb_freeze, if_insn, id_insn, ex_insn, abort_mvspr,

   id_branch_op, ex_branch_op, ex_branch_taken, pc_we,

   rf_addra, rf_addrb, rf_rda, rf_rdb, alu_op, alu_op2, mac_op,

   comp_op, rf_addrw, rfwb_op, fpu_op,

   wb_insn, id_simm, ex_simm, id_branch_addrtarget, ex_branch_addrtarget, sel_a,

   sel_b, id_lsu_op,

   cust5_op, cust5_limm, id_pc, ex_pc, du_hwbkpt,

   multicycle, wait_on, wbforw_valid, sig_syscall, sig_trap,

   force_dslot_fetch, no_more_dslot, id_void, ex_void, ex_spr_read,

   ex_spr_write, du_flush_pipe,

   id_mac_op, id_macrc_op, ex_macrc_op, rfe, except_illegal, dc_no_writethrough

   );

//

// I/O

//

input                                   clk;

input                                   rst;

input                                   id_freeze;

input                                   ex_freeze /* verilator public */;

input                                   wb_freeze /* verilator public */;

output                                  if_flushpipe;

output                                  id_flushpipe;

output                                  ex_flushpipe;

output                                  wb_flushpipe;

input                                   extend_flush;

input                                   except_flushpipe;

input                           abort_mvspr ;

input   [31:0]                   if_insn;

output  [31:0]                   id_insn;

output  [31:0]                   ex_insn /* verilator public */;

output  [`OR1200_BRANCHOP_WIDTH-1:0]             ex_branch_op;

output  [`OR1200_BRANCHOP_WIDTH-1:0]             id_branch_op;

input                                           ex_branch_taken;

output  [`OR1200_REGFILE_ADDR_WIDTH-1:0] rf_addrw;

output  [`OR1200_REGFILE_ADDR_WIDTH-1:0] rf_addra;

output  [`OR1200_REGFILE_ADDR_WIDTH-1:0] rf_addrb;

output                                  rf_rda;

output                                  rf_rdb;

output  [`OR1200_ALUOP_WIDTH-1:0]                alu_op;

output [`OR1200_ALUOP2_WIDTH-1:0]                alu_op2;

output  [`OR1200_MACOP_WIDTH-1:0]                mac_op;

output  [`OR1200_RFWBOP_WIDTH-1:0]               rfwb_op;

output  [`OR1200_FPUOP_WIDTH-1:0]                fpu_op;

input                                   pc_we;

output  [31:0]                           wb_insn;

output  [31:2]                          id_branch_addrtarget;

output  [31:2]                          ex_branch_addrtarget;

output  [`OR1200_SEL_WIDTH-1:0]          sel_a;

output  [`OR1200_SEL_WIDTH-1:0]          sel_b;

output  [`OR1200_LSUOP_WIDTH-1:0]                id_lsu_op;

output  [`OR1200_COMPOP_WIDTH-1:0]               comp_op;

output  [`OR1200_MULTICYCLE_WIDTH-1:0]           multicycle;

output  [`OR1200_WAIT_ON_WIDTH-1:0]              wait_on;

output  [4:0]                            cust5_op;

output  [5:0]                            cust5_limm;

input   [31:0]                          id_pc;

input   [31:0]                          ex_pc;

output  [31:0]                           id_simm;

output  [31:0]                           ex_simm;

input                                   wbforw_valid;

input                                   du_hwbkpt;

output                                  sig_syscall;

output                                  sig_trap;

output                                  force_dslot_fetch;

output                                  no_more_dslot;

output                                  id_void;

output                                  ex_void;

output                                  ex_spr_read;

output                                  ex_spr_write;

output  [`OR1200_MACOP_WIDTH-1:0]        id_mac_op;

output                                  id_macrc_op;

output                                  ex_macrc_op;

output                                  rfe;

output                                  except_illegal;

output                                  dc_no_writethrough;

input                                   du_flush_pipe;

//

// Internal wires and regs

//

reg     [`OR1200_BRANCHOP_WIDTH-1:0]             id_branch_op;

reg     [`OR1200_BRANCHOP_WIDTH-1:0]             ex_branch_op;

reg     [`OR1200_ALUOP_WIDTH-1:0]                alu_op;

reg [`OR1200_ALUOP2_WIDTH-1:0]                   alu_op2;

wire                                    if_maci_op;

`ifdef OR1200_MAC_IMPLEMENTED

reg     [`OR1200_MACOP_WIDTH-1:0]                ex_mac_op;

reg     [`OR1200_MACOP_WIDTH-1:0]                id_mac_op;

wire    [`OR1200_MACOP_WIDTH-1:0]                mac_op;

reg                                     ex_macrc_op;

`else

wire    [`OR1200_MACOP_WIDTH-1:0]                mac_op;

wire                                    ex_macrc_op;

`endif

reg     [31:0]                           id_insn /* verilator public */;

reg     [31:0]                           ex_insn /* verilator public */;

reg     [31:0]                           wb_insn /* verilator public */;

reg     [`OR1200_REGFILE_ADDR_WIDTH-1:0] rf_addrw;

reg     [`OR1200_REGFILE_ADDR_WIDTH-1:0] wb_rfaddrw;

reg     [`OR1200_RFWBOP_WIDTH-1:0]               rfwb_op;

reg     [`OR1200_SEL_WIDTH-1:0]          sel_a;

reg     [`OR1200_SEL_WIDTH-1:0]          sel_b;

reg                                     sel_imm;

reg     [`OR1200_LSUOP_WIDTH-1:0]                id_lsu_op;

reg     [`OR1200_COMPOP_WIDTH-1:0]               comp_op;

reg     [`OR1200_MULTICYCLE_WIDTH-1:0]           multicycle;

reg     [`OR1200_WAIT_ON_WIDTH-1:0]              wait_on;

reg     [31:0]                           id_simm;

reg     [31:0]                           ex_simm;

reg                                     sig_syscall;

reg                                     sig_trap;

reg                                     except_illegal;

wire                                    id_void;

wire                                    ex_void;

wire                                    wb_void;

reg                                     ex_delayslot_dsi;

reg                                     ex_delayslot_nop;

reg                                     spr_read;

reg                                     spr_write;

reg     [31:2]                          ex_branch_addrtarget;

`ifdef OR1200_DC_NOSTACKWRITETHROUGH

reg                                     dc_no_writethrough;

`endif

//

// Register file read addresses

//

assign rf_addra = if_insn[20:16];

assign rf_addrb = if_insn[15:11];

assign rf_rda = if_insn[31] || if_maci_op;

assign rf_rdb = if_insn[30];

//

// Force fetch of delay slot instruction when jump/branch is preceeded by 

// load/store instructions

//

assign force_dslot_fetch = 1'b0;

assign no_more_dslot = (|ex_branch_op & !id_void & ex_branch_taken) |

                       (ex_branch_op == `OR1200_BRANCHOP_RFE);

assign id_void = (id_insn[31:26] == `OR1200_OR32_NOP) & id_insn[16];

assign ex_void = (ex_insn[31:26] == `OR1200_OR32_NOP) & ex_insn[16];

assign wb_void = (wb_insn[31:26] == `OR1200_OR32_NOP) & wb_insn[16];

assign ex_spr_write = spr_write && !abort_mvspr;

assign ex_spr_read = spr_read && !abort_mvspr;

//

// ex_delayslot_dsi: delay slot insn is in EX stage

// ex_delayslot_nop: (filler) nop insn is in EX stage (before nops 

//                   jump/branch was executed)

//

//  ex_delayslot_dsi & !ex_delayslot_nop - DS insn in EX stage

//  !ex_delayslot_dsi & ex_delayslot_nop - NOP insn in EX stage, 

//       next different is DS insn, previous different was Jump/Branch

//  !ex_delayslot_dsi & !ex_delayslot_nop - normal insn in EX stage

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE) begin

                ex_delayslot_nop <=  1'b0;

                ex_delayslot_dsi <=  1'b0;

        end

        else if (!ex_freeze & !ex_delayslot_dsi & ex_delayslot_nop) begin

                ex_delayslot_nop <=  id_void;

                ex_delayslot_dsi <=  !id_void;

        end

        else if (!ex_freeze & ex_delayslot_dsi & !ex_delayslot_nop) begin

                ex_delayslot_nop <=  1'b0;

                ex_delayslot_dsi <=  1'b0;

        end

        else if (!ex_freeze) begin

                ex_delayslot_nop <=  id_void && ex_branch_taken &&

                                     (ex_branch_op != `OR1200_BRANCHOP_NOP) &&

                                     (ex_branch_op != `OR1200_BRANCHOP_RFE);

                ex_delayslot_dsi <=  !id_void && ex_branch_taken &&

                                     (ex_branch_op != `OR1200_BRANCHOP_NOP) &&

                                     (ex_branch_op != `OR1200_BRANCHOP_RFE);

        end

end

//

// Flush pipeline

//

assign if_flushpipe = except_flushpipe | pc_we | extend_flush | du_flush_pipe;

assign id_flushpipe = except_flushpipe | pc_we | extend_flush | du_flush_pipe;

assign ex_flushpipe = except_flushpipe | pc_we | extend_flush | du_flush_pipe;

assign wb_flushpipe = except_flushpipe | pc_we | extend_flush | du_flush_pipe;

//

// EX Sign/Zero extension of immediates

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                ex_simm <=  32'h0000_0000;

        else if (!ex_freeze) begin

                ex_simm <=  id_simm;

        end

end

//

// ID Sign/Zero extension of immediate

//

always @(id_insn) begin

        case (id_insn[31:26])     // synopsys parallel_case

        // l.addi

        `OR1200_OR32_ADDI:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        // l.addic

        `OR1200_OR32_ADDIC:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        // l.lxx (load instructions)

        `OR1200_OR32_LWZ, `OR1200_OR32_LWS,

   `OR1200_OR32_LBZ, `OR1200_OR32_LBS,

        `OR1200_OR32_LHZ, `OR1200_OR32_LHS:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        // l.muli

        `ifdef OR1200_MULT_IMPLEMENTED

        `OR1200_OR32_MULI:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        `endif

        // l.maci

        `ifdef OR1200_MAC_IMPLEMENTED

        `OR1200_OR32_MACI:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        `endif

        // l.mtspr

        `OR1200_OR32_MTSPR:

                id_simm = {16'b0, id_insn[25:21], id_insn[10:0]};

        // l.sxx (store instructions)

        `OR1200_OR32_SW, `OR1200_OR32_SH, `OR1200_OR32_SB:

                id_simm = {{16{id_insn[25]}}, id_insn[25:21], id_insn[10:0]};

        // l.xori

        `OR1200_OR32_XORI:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        // l.sfxxi (SFXX with immediate)

        `OR1200_OR32_SFXXI:

                id_simm = {{16{id_insn[15]}}, id_insn[15:0]};

        // Instructions with no or zero extended immediate

        default:

                id_simm = {{16'b0}, id_insn[15:0]};

        endcase

end

//

// ID Sign extension of branch offset

//

assign id_branch_addrtarget = {{4{id_insn[25]}}, id_insn[25:0]} + id_pc[31:2];

//

// EX Sign extension of branch offset

//

// pipeline ID and EX branch target address 

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                ex_branch_addrtarget <=  0;

        else if (!ex_freeze)

                ex_branch_addrtarget <=  id_branch_addrtarget;

end

// not pipelined

//assign ex_branch_addrtarget = {{4{ex_insn[25]}}, ex_insn[25:0]} + ex_pc[31:2];

//

// l.maci in IF stage

//

`ifdef OR1200_MAC_IMPLEMENTED

assign if_maci_op = (if_insn[31:26] == `OR1200_OR32_MACI);

`else

assign if_maci_op = 1'b0;

`endif

//

// l.macrc in ID stage

//

`ifdef OR1200_MAC_IMPLEMENTED

assign id_macrc_op = (id_insn[31:26] == `OR1200_OR32_MACRC) & id_insn[16];

`else

assign id_macrc_op = 1'b0;

`endif

//

// l.macrc in EX stage

//

`ifdef OR1200_MAC_IMPLEMENTED

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                ex_macrc_op <=  1'b0;

        else if (!ex_freeze & id_freeze | ex_flushpipe)

                ex_macrc_op <=  1'b0;

        else if (!ex_freeze)

                ex_macrc_op <=  id_macrc_op;

end

`else

assign ex_macrc_op = 1'b0;

`endif

//

// cust5_op, cust5_limm (L immediate)

//

assign cust5_op = ex_insn[4:0];

assign cust5_limm = ex_insn[10:5];

//

//

//

assign rfe = (id_branch_op == `OR1200_BRANCHOP_RFE) |

             (ex_branch_op == `OR1200_BRANCHOP_RFE);

`ifdef verilator

   // Function to access wb_insn (for Verilator). Have to hide this from

   // simulator, since functions with no inputs are not allowed in IEEE

   // 1364-2001.

   function [31:0] get_wb_insn;

      // verilator public

      get_wb_insn = wb_insn;

   endfunction // get_wb_insn

   // Function to access id_insn (for Verilator). Have to hide this from

   // simulator, since functions with no inputs are not allowed in IEEE

   // 1364-2001.

   function [31:0] get_id_insn;

      // verilator public

      get_id_insn = id_insn;

   endfunction // get_id_insn

   // Function to access ex_insn (for Verilator). Have to hide this from

   // simulator, since functions with no inputs are not allowed in IEEE

   // 1364-2001.

   function [31:0] get_ex_insn;

      // verilator public

      get_ex_insn = ex_insn;

   endfunction // get_ex_insn

`endif

//

// Generation of sel_a

//

always @(rf_addrw or id_insn or rfwb_op or wbforw_valid or wb_rfaddrw)

        if ((id_insn[20:16] == rf_addrw) && rfwb_op[0])

                sel_a = `OR1200_SEL_EX_FORW;

        else if ((id_insn[20:16] == wb_rfaddrw) && wbforw_valid)

                sel_a = `OR1200_SEL_WB_FORW;

        else

                sel_a = `OR1200_SEL_RF;

//

// Generation of sel_b

//

always @(rf_addrw or sel_imm or id_insn or rfwb_op or wbforw_valid or

         wb_rfaddrw)

        if (sel_imm)

                sel_b = `OR1200_SEL_IMM;

        else if ((id_insn[15:11] == rf_addrw) && rfwb_op[0])

                sel_b = `OR1200_SEL_EX_FORW;

        else if ((id_insn[15:11] == wb_rfaddrw) && wbforw_valid)

                sel_b = `OR1200_SEL_WB_FORW;

        else

                sel_b = `OR1200_SEL_RF;

//

// Decode of multicycle

//

always @(id_insn) begin

  case (id_insn[31:26])         // synopsys parallel_case

    // l.rfe

    `OR1200_OR32_RFE,

    // l.mfspr

    `OR1200_OR32_MFSPR:

      multicycle = `OR1200_TWO_CYCLES;  // to read from ITLB/DTLB (sync RAMs)

    // Single cycle instructions

    default: begin

      multicycle = `OR1200_ONE_CYCLE;

    end

  endcase

end // always @ (id_insn)

//

// Encode wait_on signal

//    

always @(id_insn) begin

   case (id_insn[31:26])                // synopsys parallel_case

     `OR1200_OR32_ALU:

       wait_on =  ( 1'b0

`ifdef OR1200_DIV_IMPLEMENTED

                     | (id_insn[4:0] == `OR1200_ALUOP_DIV)

                     | (id_insn[4:0] == `OR1200_ALUOP_DIVU)

`endif

`ifdef OR1200_MULT_IMPLEMENTED

                     | (id_insn[4:0] == `OR1200_ALUOP_MUL)

                     | (id_insn[4:0] == `OR1200_ALUOP_MULU)

`endif

                    ) ? `OR1200_WAIT_ON_MULTMAC : `OR1200_WAIT_ON_NOTHING;

`ifdef OR1200_MULT_IMPLEMENTED

`ifdef OR1200_MAC_IMPLEMENTED

     `OR1200_OR32_MACMSB,

     `OR1200_OR32_MACI,

`endif

     `OR1200_OR32_MULI:

         wait_on = `OR1200_WAIT_ON_MULTMAC;

`endif

`ifdef OR1200_MAC_IMPLEMENTED

     `OR1200_OR32_MACRC:

         wait_on = id_insn[16] ? `OR1200_WAIT_ON_MULTMAC :

                                 `OR1200_WAIT_ON_NOTHING;

`endif

`ifdef OR1200_FPU_IMPLEMENTED

       `OR1200_OR32_FLOAT: begin

         wait_on = id_insn[`OR1200_FPUOP_DOUBLE_BIT] ? 0 : `OR1200_WAIT_ON_FPU;

       end

`endif

`ifndef OR1200_DC_WRITEHROUGH

     // l.mtspr

     `OR1200_OR32_MTSPR: begin

        wait_on = `OR1200_WAIT_ON_MTSPR;

     end

`endif

     default: begin

        wait_on = `OR1200_WAIT_ON_NOTHING;

     end

   endcase // case (id_insn[31:26])

end // always @ (id_insn)

//

// Register file write address

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                rf_addrw <=  5'd0;

        else if (!ex_freeze & id_freeze)

                rf_addrw <=  5'd00;

        else if (!ex_freeze)

                case (id_insn[31:26])   // synopsys parallel_case

                        `OR1200_OR32_JAL, `OR1200_OR32_JALR:

                                rf_addrw <=  5'd09;     // link register r9

                        default:

                                rf_addrw <=  id_insn[25:21];

                endcase

end

//

// rf_addrw in wb stage (used in forwarding logic)

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                wb_rfaddrw <=  5'd0;

        else if (!wb_freeze)

                wb_rfaddrw <=  rf_addrw;

end

//

// Instruction latch in id_insn

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                id_insn <=  {`OR1200_OR32_NOP, 26'h041_0000};

        else if (id_flushpipe)

                id_insn <=  {`OR1200_OR32_NOP, 26'h041_0000};        // NOP -> id_insn[16] must be 1

        else if (!id_freeze) begin

                id_insn <=  if_insn;

`ifdef OR1200_VERBOSE

// synopsys translate_off

                $display("%t: id_insn <= %h", $time, if_insn);

// synopsys translate_on

`endif

        end

end

//

// Instruction latch in ex_insn

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                ex_insn <=  {`OR1200_OR32_NOP, 26'h041_0000};

        else if (!ex_freeze & id_freeze | ex_flushpipe)

                ex_insn <=  {`OR1200_OR32_NOP, 26'h041_0000};   // NOP -> ex_insn[16] must be 1

        else if (!ex_freeze) begin

                ex_insn <=  id_insn;

`ifdef OR1200_VERBOSE

// synopsys translate_off

                $display("%t: ex_insn <= %h", $time, id_insn);

// synopsys translate_on

`endif

        end

end

//

// Instruction latch in wb_insn

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                wb_insn <=  {`OR1200_OR32_NOP, 26'h041_0000};

        // wb_insn should not be changed by exceptions due to correct 

        // recording of display_arch_state in the or1200_monitor! 

        // wb_insn changed by exception is not used elsewhere! 

        else if (!wb_freeze) begin

                wb_insn <=  ex_insn;

        end

end

//

// Decode of sel_imm

//

always @(posedge clk or `OR1200_RST_EVENT rst) begin

        if (rst == `OR1200_RST_VALUE)

                sel_imm <=  1'b0;

        else if (!id_freeze) begin

          case (if_insn[31:26])         // synopsys parallel_case

            // j.jalr

            `OR1200_OR32_JALR:

              sel_imm <=  1'b0;

            // l.jr

            `OR1200_OR32_JR:

              sel_imm <=  1'b0;

            // l.rfe

            `OR1200_OR32_RFE:

              sel_imm <=  1'b0;

            // l.mfspr

            `OR1200_OR32_MFSPR:

              sel_imm <=  1'b0;

            // l.mtspr

            `OR1200_OR32_MTSPR:

              sel_imm <=  1'b0;

            // l.sys, l.brk and all three sync insns

            `OR1200_OR32_XSYNC:

              sel_imm <=  1'b0;

            // l.mac/l.msb

`ifdef OR1200_MAC_IMPLEMENTED

            `OR1200_OR32_MACMSB:

              sel_imm <=  1'b0;

`endif

            // l.sw

            `OR1200_OR32_SW:

              sel_imm <=  1'b0;

            // l.sb

            `OR1200_OR32_SB:

              sel_imm <=  1'b0;

            // l.sh

            `OR1200_OR32_SH:

              sel_imm <=  1'b0;

            // ALU instructions except the one with immediate

            `OR1200_OR32_ALU:

              sel_imm <=  1'b0;

            // SFXX instructions

            `OR1200_OR32_SFXX:

              sel_imm <=  1'b0;

`ifdef OR1200_IMPL_ALU_CUST5

            // l.cust5 instructions

            `OR1200_OR32_CUST5:

              sel_imm <=  1'b0;

`endif

`ifdef OR1200_FPU_IMPLEMENTED

            // FPU instructions

            `OR1200_OR32_FLOAT:

              sel_imm <=  1'b0;

`endif

            // l.nop

            `OR1200_OR32_NOP:

              sel_imm <=  1'b0;

            // All instructions with immediates

            default: begin

              sel_imm <=  1'b1;

            end