Subversion Repositories altor32

//-----------------------------------------------------------------
//                           AltOR32 
//                Alternative Lightweight OpenRisc 
//                            V2.0
//                     Ultra-Embedded.com
//                   Copyright 2011 - 2013
//
//               Email: admin@ultra-embedded.com
//
//                       License: LGPL
//-----------------------------------------------------------------
//
// Copyright (C) 2011 - 2013 Ultra-Embedded.com
//
// 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, write to the 
// Free Software Foundation, Inc., 59 Temple Place, Suite 330, 
// Boston, MA  02111-1307  USA
//-----------------------------------------------------------------
 
//`define CONF_CORE_DEBUG
//`define CONF_CORE_TRACE
 
//-----------------------------------------------------------------
// Includes
//-----------------------------------------------------------------
`include "altor32_defs.v"
 
//-----------------------------------------------------------------
// Module - Simple AltOR32 (non-pipelined, small, single WB interface)
//-----------------------------------------------------------------
module altor32_lite
(
    // General
    input               clk_i /*verilator public*/,
    input               rst_i /*verilator public*/,
 
    // Maskable interrupt    
    input               intr_i /*verilator public*/,
 
    // Unmaskable interrupt
    input               nmi_i /*verilator public*/,
 
    // Enable core
    input               enable_i /*verilator public*/,
 
    // Fault
    output reg          fault_o /*verilator public*/,
 
    // Breakpoint / Trap
    output reg          break_o /*verilator public*/,
 
    // Memory interface
    output reg [31:0]   mem_addr_o /*verilator public*/,
    input [31:0]        mem_dat_i /*verilator public*/,
    output reg [31:0]   mem_dat_o /*verilator public*/,
    output [2:0]        mem_cti_o /*verilator public*/,
    output reg          mem_cyc_o /*verilator public*/,
    output reg          mem_stb_o /*verilator public*/,
    output reg          mem_we_o /*verilator public*/,
    output reg [3:0]    mem_sel_o /*verilator public*/,
    input               mem_stall_i/*verilator public*/,
    input               mem_ack_i/*verilator public*/ 
);
 
//-----------------------------------------------------------------
// Params
//-----------------------------------------------------------------
parameter           BOOT_VECTOR         = 32'h00000000;
parameter           ISR_VECTOR          = 32'h00000000;
parameter           REGISTER_FILE_TYPE  = "SIMULATION";
parameter           SUPPORT_32REGS      = "ENABLED";
 
//-----------------------------------------------------------------
// Registers
//-----------------------------------------------------------------
 
// PC
reg [31:0]  r_pc;
 
// Exception saved program counter
reg [31:0]  r_epc;
 
// Supervisor register
reg [31:0]  r_sr;
 
// Exception saved supervisor register
reg [31:0]  r_esr;
 
// Destination register number (post execute stage)
reg [4:0]   r_e_rd;
 
// ALU input A
reg [31:0]  r_e_alu_a;
 
// ALU input B
reg [31:0]  r_e_alu_b;
 
// ALU output
wire [31:0] r_e_result;
 
// ALU Carry
wire        alu_carry_out;
wire        alu_carry_update;
 
// ALU operation selection
reg [3:0]   r_e_alu_func;
 
// Delayed NMI
reg         r_nmi;
 
// SIM PUTC
`ifdef SIM_EXT_PUTC
    reg [7:0] r_putc;
`endif
 
wire [4:0]  w_ra;
wire [4:0]  w_rb;
wire [4:0]  w_rd;
 
wire [31:0] w_reg_ra;
wire [31:0] w_reg_rb;
 
reg [31:0]  r_opcode;
 
reg [31:0]  r_load_result;
 
reg [1:0]   mem_offset;
 
// Current state
parameter STATE_IDLE        = 0;
parameter STATE_FETCH       = 1;
parameter STATE_FETCH_WAIT  = 2;
parameter STATE_EXEC        = 3;
parameter STATE_MEM         = 4;
parameter STATE_WRITE_BACK  = 5;
 
reg [3:0]   state;
 
//-----------------------------------------------------------------
// Instantiation
//-----------------------------------------------------------------
 
// ALU
altor32_alu alu
(
    // ALU operation select
    .op_i(r_e_alu_func),
 
    // Operands
    .a_i(r_e_alu_a),
    .b_i(r_e_alu_b),
    .c_i(r_sr[`OR32_SR_CY]),
 
    // Result
    .p_o(r_e_result),
 
    // Carry
    .c_o(alu_carry_out),
    .c_update_o(alu_carry_update)
);
 
// Writeback result
wire [31:0] w_write_res     = (state == STATE_MEM) ? r_load_result : r_e_result;
 
// Writeback enable
wire        w_write_en      = (state == STATE_MEM & mem_ack_i) | (state == STATE_WRITE_BACK);
 
// Register file
generate
if (REGISTER_FILE_TYPE == "XILINX")
begin : REGFILE_XIL
    altor32_regfile_xil
    #(
        .SUPPORT_32REGS(SUPPORT_32REGS)
    )
    reg_bank
    (
        // Clocking
        .clk_i(clk_i),
        .rst_i(rst_i),
        .wr_i(w_write_en),
 
        // Tri-port
        .rs_i(w_ra),
        .rt_i(w_rb),
        .rd_i(r_e_rd),
        .reg_rs_o(w_reg_ra),
        .reg_rt_o(w_reg_rb),
        .reg_rd_i(w_write_res)
    );
end
else if (REGISTER_FILE_TYPE == "ALTERA")
begin : REGFILE_ALT
    altor32_regfile_alt
    #(
        .SUPPORT_32REGS(SUPPORT_32REGS)
    )    
    reg_bank
    (
        // Clocking
        .clk_i(clk_i),
        .rst_i(rst_i),
        .wr_i(w_write_en),
 
        // Tri-port
        .rs_i(w_ra),
        .rt_i(w_rb),
        .rd_i(r_e_rd),
        .reg_rs_o(w_reg_ra),
        .reg_rt_o(w_reg_rb),
        .reg_rd_i(w_write_res)
    );
end
else
begin : REGFILE_SIM
    altor32_regfile_sim
    #(
        .SUPPORT_32REGS(SUPPORT_32REGS)
    )
    reg_bank
    (
        // Clocking
        .clk_i(clk_i),
        .rst_i(rst_i),
        .wr_i(w_write_en),
 
        // Tri-port
        .rs_i(w_ra),
        .rt_i(w_rb),
        .rd_i(r_e_rd),
        .reg_rs_o(w_reg_ra),
        .reg_rt_o(w_reg_rb),
        .reg_rd_i(w_write_res)
    );
end
endgenerate
 
//-----------------------------------------------------------------
// Opcode decode
//-----------------------------------------------------------------
reg [7:0]  inst_r;
reg [7:0]  alu_op_r;
reg [1:0]  shift_op_r;
reg [15:0] sfxx_op_r;
reg [15:0] uint16_r;
reg [31:0] uint32_r;
reg [31:0] int32_r;
reg [31:0] store_int32_r;
reg [15:0] mxspr_uint16_r;
reg [31:0] target_int26_r;
reg [31:0] reg_ra_r;
reg [31:0] reg_rb_r;
reg [31:0] shift_rb_r;
reg [31:0] shift_imm_r;
 
always @ *
begin
    // Instruction
    inst_r               = {2'b00,r_opcode[31:26]};
 
    // Sub instructions
    alu_op_r             = {r_opcode[9:6],r_opcode[3:0]};
    sfxx_op_r            = {5'b00,r_opcode[31:21]};
    shift_op_r           = r_opcode[7:6];
 
    // Branch target
    target_int26_r       = sign_extend_imm26(r_opcode[25:0]);
 
    // Store immediate
    store_int32_r        = sign_extend_imm16({r_opcode[25:21],r_opcode[10:0]});
 
    // Signed & unsigned imm -> 32-bits
    uint16_r             = r_opcode[15:0];
    int32_r              = sign_extend_imm16(r_opcode[15:0]);
    uint32_r             = extend_imm16(r_opcode[15:0]);
 
    // Register values [ra/rb]
    reg_ra_r             = w_reg_ra;
    reg_rb_r             = w_reg_rb;
 
    // Shift ammount (from register[rb])
    shift_rb_r           = {26'b00,w_reg_rb[5:0]};
 
    // Shift ammount (from immediate)
    shift_imm_r          = {26'b00,r_opcode[5:0]};
 
    // MTSPR/MFSPR operand
    mxspr_uint16_r       = (w_reg_ra[15:0] | {5'b00000,r_opcode[10:0]});
end
 
//-----------------------------------------------------------------
// Instruction Decode
//-----------------------------------------------------------------
wire inst_add_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_ADD);  // l.add
wire inst_addc_w    = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_ADDC); // l.addc
wire inst_and_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_AND);  // l.and
wire inst_or_w      = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_OR);   // l.or
wire inst_sll_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_SLL);  // l.sll
wire inst_sw_ra     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_SRA);  // l.sra
wire inst_srl_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_SRL);  // l.srl
wire inst_sub_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_SUB);  // l.sub
wire inst_xor_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_XOR);  // l.xor
wire inst_mul_w     = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_MUL);  // l.mul
wire inst_mulu_w    = (inst_r == `INST_OR32_ALU) & (alu_op_r == `INST_OR32_MULU); // l.mulu
 
wire inst_addi_w    = (inst_r == `INST_OR32_ADDI);  // l.addi
wire inst_andi_w    = (inst_r == `INST_OR32_ANDI);  // l.andi
wire inst_bf_w      = (inst_r == `INST_OR32_BF);    // l.bf
wire inst_bnf_w     = (inst_r == `INST_OR32_BNF);   // l.bnf
wire inst_j_w       = (inst_r == `INST_OR32_J);     // l.j
wire inst_jal_w     = (inst_r == `INST_OR32_JAL);   // l.jal
wire inst_jalr_w    = (inst_r == `INST_OR32_JALR);  // l.jalr
wire inst_jr_w      = (inst_r == `INST_OR32_JR);    // l.jr
wire inst_lbs_w     = (inst_r == `INST_OR32_LBS);   // l.lbs
wire inst_lhs_w     = (inst_r == `INST_OR32_LHS);   // l.lhs
wire inst_lws_w     = (inst_r == `INST_OR32_LWS);   // l.lws
wire inst_lbz_w     = (inst_r == `INST_OR32_LBZ);   // l.lbz
wire inst_lhz_w     = (inst_r == `INST_OR32_LHZ);   // l.lhz
wire inst_lwz_w     = (inst_r == `INST_OR32_LWZ);   // l.lwz
wire inst_mfspr_w   = (inst_r == `INST_OR32_MFSPR); // l.mfspr
wire inst_mtspr_w   = (inst_r == `INST_OR32_MTSPR); // l.mtspr
wire inst_movhi_w   = (inst_r == `INST_OR32_MOVHI); // l.movhi
wire inst_nop_w     = (inst_r == `INST_OR32_NOP);   // l.nop
wire inst_ori_w     = (inst_r == `INST_OR32_ORI);   // l.ori
wire inst_rfe_w     = (inst_r == `INST_OR32_RFE);   // l.rfe
 
wire inst_sb_w      = (inst_r == `INST_OR32_SB);    // l.sb
wire inst_sh_w      = (inst_r == `INST_OR32_SH);    // l.sh
wire inst_sw_w      = (inst_r == `INST_OR32_SW);    // l.sw
 
wire inst_slli_w    = (inst_r == `INST_OR32_SHIFTI) & (shift_op_r == `INST_OR32_SLLI);  // l.slli
wire inst_srai_w    = (inst_r == `INST_OR32_SHIFTI) & (shift_op_r == `INST_OR32_SRAI);  // l.srai
wire inst_srli_w    = (inst_r == `INST_OR32_SHIFTI) & (shift_op_r == `INST_OR32_SRLI);  // l.srli
 
wire inst_xori_w    = (inst_r == `INST_OR32_XORI);   // l.xori
 
wire inst_sfxx_w    = (inst_r == `INST_OR32_SFXX);
wire inst_sfxxi_w   = (inst_r == `INST_OR32_SFXXI);
 
wire inst_sfeq_w    = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFEQ);   // l.sfeq
wire inst_sfges_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFGES);  // l.sfges
 
wire inst_sfgeu_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFGEU);  // l.sfgeu
wire inst_sfgts_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFGTS);  // l.sfgts
wire inst_sfgtu_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFGTU);  // l.sfgtu
wire inst_sfles_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFLES);  // l.sfles
wire inst_sfleu_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFLEU);  // l.sfleu
wire inst_sflts_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFLTS);  // l.sflts
wire inst_sfltu_w   = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFLTU);  // l.sfltu
wire inst_sfne_w    = (inst_r == `INST_OR32_SFXX) & (sfxx_op_r == `INST_OR32_SFNE);   // l.sfne
 
wire inst_sfeqi_w   = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFEQI);  // l.sfeqi
wire inst_sfgesi_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFGESI); // l.sfgesi
wire inst_sfgeui_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFGEUI); // l.sfgeui
wire inst_sfgtsi_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFGTSI); // l.sfgtsi
wire inst_sfgtui_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFGTUI); // l.sfgtui
wire inst_sflesi_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFLESI); // l.sflesi
 
wire inst_sfleui_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFLEUI); // l.sfleui
wire inst_sfltsi_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFLTSI); // l.sfltsi
wire inst_sfltui_w  = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFLTUI); // l.sfltui
wire inst_sfnei_w   = (inst_r == `INST_OR32_SFXXI) & (sfxx_op_r == `INST_OR32_SFNEI);  // l.sfnei
 
wire inst_sys_w     = (inst_r == `INST_OR32_MISC) & (r_opcode[31:24] == `INST_OR32_SYS);  // l.sys
wire inst_trap_w    = (inst_r == `INST_OR32_MISC) & (r_opcode[31:24] == `INST_OR32_TRAP); // l.trap
 
//-----------------------------------------------------------------
// Load/Store operation?
//-----------------------------------------------------------------
reg         load_inst_r;
reg         store_inst_r;
reg [31:0]  mem_addr_r;
always @ *
begin
    load_inst_r  = inst_lbs_w | inst_lhs_w | inst_lws_w |
                   inst_lbz_w | inst_lhz_w | inst_lwz_w;
    store_inst_r = inst_sb_w  | inst_sh_w  | inst_sw_w;
 
    // Memory address is relative to RA
    mem_addr_r = reg_ra_r + (store_inst_r ? store_int32_r : int32_r);
end
 
//-----------------------------------------------------------------
// Next State Logic
//-----------------------------------------------------------------
reg [3:0] next_state_r;
always @ *
begin
    next_state_r = state;
 
    case (state)    
    //-----------------------------------------
    // IDLE - 
    //-----------------------------------------
    STATE_IDLE :
    begin
        if (enable_i)
            next_state_r    = STATE_FETCH;
    end    
    //-----------------------------------------
    // FETCH - Fetch line from memory
    //-----------------------------------------
    STATE_FETCH :
    begin
        next_state_r    = STATE_FETCH_WAIT;
    end
    //-----------------------------------------
    // FETCH_WAIT - Wait for read responses
    //-----------------------------------------
    STATE_FETCH_WAIT:
    begin
        // Read from memory complete
        if (mem_ack_i)
            next_state_r = STATE_EXEC;
    end  
    //-----------------------------------------
    // EXEC
    //-----------------------------------------
    STATE_EXEC :
    begin
        if (load_inst_r || store_inst_r)
            next_state_r    = STATE_MEM;
        else
            next_state_r    = STATE_WRITE_BACK;
    end
    //-----------------------------------------
    // MEM
    //-----------------------------------------
    STATE_MEM :
    begin
        // Read from memory complete
        if (mem_ack_i)
            next_state_r = STATE_FETCH;
    end    
    //-----------------------------------------
    // WRITE_BACK
    //-----------------------------------------
    STATE_WRITE_BACK :
    begin
        if (enable_i)
            next_state_r    = STATE_FETCH;
    end    
    default:
        ;
   endcase
end
 
// Update state
always @ (posedge rst_i or posedge clk_i )
begin
   if (rst_i == 1'b1)
        state   <= STATE_IDLE;
   else
        state   <= next_state_r;
end
 
//-----------------------------------------------------------------
// Memory Access / Instruction Fetch
//-----------------------------------------------------------------
always @ (posedge rst_i or posedge clk_i )
begin
   if (rst_i == 1'b1)
   begin
        mem_addr_o      <= 32'h00000000;        
        mem_dat_o       <= 32'h00000000;
        mem_sel_o       <= 4'b0;
        mem_we_o        <= 1'b0;
        mem_stb_o       <= 1'b0;
        mem_cyc_o       <= 1'b0;
 
        r_opcode        <= 32'h00000000;
        mem_offset      <= 2'b0;
   end
   else
   begin
 
        if (~mem_stall_i)
            mem_stb_o    <= 1'b0;
 
        case (state)
 
            //-----------------------------------------
            // FETCH - Issue instruction fetch
            //-----------------------------------------
            STATE_FETCH :
            begin
                // Start fetch from memory
                mem_addr_o  <= r_pc;
                mem_stb_o   <= 1'b1;
                mem_we_o    <= 1'b0;
                mem_cyc_o   <= 1'b1;
            end
            //-----------------------------------------
            // FETCH_WAIT - Wait for response
            //-----------------------------------------
            STATE_FETCH_WAIT :
            begin
                // Data ready from memory?
                if (mem_ack_i)
                begin
                    r_opcode    <= mem_dat_i;
                    mem_cyc_o   <= 1'b0;                            
                end
            end
            //-----------------------------------------
            // EXEC - Issue read / write
            //-----------------------------------------            
            STATE_EXEC :
            begin
            `ifdef CONF_CORE_TRACE
                $display("%08x: Execute 0x%08x", r_pc, r_opcode);
                $display(" rA[%d] = 0x%08x", w_ra, reg_ra_r);
                $display(" rB[%d] = 0x%08x", w_rb, reg_rb_r);
            `endif
 
                case (1'b1)
                 // l.lbs l.lhs l.lws l.lbz l.lhz l.lwz
                 load_inst_r:
                 begin
                     mem_addr_o      <= {mem_addr_r[31:2], 2'b0};
                     mem_offset      <= mem_addr_r[1:0];
                     mem_dat_o       <= 32'h00000000;
                     mem_sel_o       <= 4'b1111;
                     mem_we_o        <= 1'b0;
                     mem_stb_o       <= 1'b1;
                     mem_cyc_o       <= 1'b1;   
 
      `ifdef CONF_CORE_DEBUG
                     $display(" Load from 0x%08x to R%d", mem_addr_r, w_rd);
      `endif
                 end
 
                 inst_sb_w: // l.sb
                 begin
                     mem_addr_o      <= {mem_addr_r[31:2], 2'b0};
                     mem_offset      <= mem_addr_r[1:0];
                     case (mem_addr_r[1:0])
                         2'b00 :
                         begin
                             mem_dat_o       <= {reg_rb_r[7:0],24'h000000};
                             mem_sel_o       <= 4'b1000;
                             mem_we_o        <= 1'b1;
                             mem_stb_o       <= 1'b1;
                             mem_cyc_o       <= 1'b1;
                         end
                         2'b01 :
                         begin
                             mem_dat_o       <= {{8'h00,reg_rb_r[7:0]},16'h0000};
                             mem_sel_o       <= 4'b0100;
                             mem_we_o        <= 1'b1;
                             mem_stb_o       <= 1'b1;
                             mem_cyc_o       <= 1'b1;
                         end
                         2'b10 :
                         begin
                             mem_dat_o       <= {{16'h0000,reg_rb_r[7:0]},8'h00};
                             mem_sel_o       <= 4'b0010;
                             mem_we_o        <= 1'b1;
                             mem_stb_o       <= 1'b1;
                             mem_cyc_o       <= 1'b1;
                         end
                         2'b11 :
                         begin
                             mem_dat_o       <= {24'h000000,reg_rb_r[7:0]};
                             mem_sel_o       <= 4'b0001;
                             mem_we_o        <= 1'b1;
                             mem_stb_o       <= 1'b1;
                             mem_cyc_o       <= 1'b1;
                         end
                         default :
                            ;
                     endcase
                 end
 
                inst_sh_w: // l.sh
                begin
                     mem_addr_o      <= {mem_addr_r[31:2], 2'b0};
                     mem_offset      <= mem_addr_r[1:0];
                     case (mem_addr_r[1:0])
                         2'b00 :
                         begin
                             mem_dat_o       <= {reg_rb_r[15:0],16'h0000};
                             mem_sel_o       <= 4'b1100;
                             mem_we_o        <= 1'b1;
                             mem_stb_o       <= 1'b1;
                             mem_cyc_o       <= 1'b1;
                         end
                         2'b10 :
                         begin
                             mem_dat_o       <= {16'h0000,reg_rb_r[15:0]};
                             mem_sel_o       <= 4'b0011;
                             mem_we_o        <= 1'b1;
                             mem_stb_o       <= 1'b1;
                             mem_cyc_o       <= 1'b1;
                         end
                         default :
                            ;
                     endcase
                end
 
                inst_sw_w: // l.sw
                begin
                     mem_addr_o      <= {mem_addr_r[31:2], 2'b0};
                     mem_offset      <= mem_addr_r[1:0];
                     mem_dat_o       <= reg_rb_r;
                     mem_sel_o       <= 4'b1111;
                     mem_we_o        <= 1'b1;
                     mem_stb_o       <= 1'b1;
                     mem_cyc_o       <= 1'b1;
 
      `ifdef CONF_CORE_DEBUG
                     $display(" Store R%d to 0x%08x = 0x%08x", w_rb, {mem_addr_r[31:2],2'b00}, reg_rb_r);
      `endif
                end
                default:
                    ;
             endcase
            end
            //-----------------------------------------
            // MEM - Wait for response
            //-----------------------------------------
            STATE_MEM :
            begin
                // Data ready from memory?
                if (mem_ack_i)
                begin
                    mem_cyc_o   <= 1'b0;
                end
            end            
            default:
                ;
           endcase
   end
end
 
assign mem_cti_o        = 3'b111;
 
// If simulation, RA = 03 if NOP instruction
`ifdef SIMULATION
    wire [7:0] v_fetch_inst = {2'b00, r_opcode[31:26]};
    wire       v_is_nop     = (v_fetch_inst == `INST_OR32_NOP);
    assign     w_ra         = v_is_nop ? 5'd3 : r_opcode[20:16];
`else
    assign     w_ra         = r_opcode[20:16];
`endif
 
assign w_rb        = r_opcode[15:11];
assign w_rd        = r_opcode[25:21];
 
//-----------------------------------------------------------------
// Next PC
//-----------------------------------------------------------------
reg [31:0]  next_pc_r;
 
always @ *
begin
    // Next expected PC (current PC + 4)
    next_pc_r  = (r_pc + 4);
end
 
//-----------------------------------------------------------------
// Next SR
//-----------------------------------------------------------------
reg [31:0]  next_sr_r;
reg         compare_result_r;
always @ *
begin
    next_sr_r = r_sr;
 
    // Latch carry if updated
    if (alu_carry_update)
        next_sr_r[`OR32_SR_CY] = alu_carry_out;    
 
    case (1'b1)
      inst_mtspr_w:
      begin
          case (mxspr_uint16_r)
          // SR - Supervision register
          `SPR_REG_SR:
          begin
              next_sr_r[`OR32_SR_F]     = reg_rb_r[`OR32_SR_F];
              next_sr_r[`OR32_SR_CY]    = reg_rb_r[`OR32_SR_CY];
              next_sr_r[`OR32_SR_IEE]   = reg_rb_r[`OR32_SR_IEE];
          end
          default:
            ;        
          endcase
      end
      inst_rfe_w:
      begin
          next_sr_r[`OR32_SR_F]         = r_esr[`OR32_SR_F];
          next_sr_r[`OR32_SR_CY]        = r_esr[`OR32_SR_CY];
          next_sr_r[`OR32_SR_IEE]       = r_esr[`OR32_SR_IEE];
      end          
      inst_sfxx_w,
      inst_sfxxi_w:
           next_sr_r[`OR32_SR_F] = compare_result_r;
      default:
        ;
    endcase
end
 
//-----------------------------------------------------------------
// Next EPC/ESR
//-----------------------------------------------------------------
reg [31:0]  next_epc_r;
reg [31:0]  next_esr_r;
 
always @ *
begin
    next_epc_r = r_epc;
    next_esr_r = r_esr;
 
    case (1'b1)
    inst_mtspr_w: // l.mtspr
    begin
       case (mxspr_uint16_r)
           // EPCR - EPC Exception saved PC
           `SPR_REG_EPCR:   next_epc_r = reg_rb_r;
 
           // ESR - Exception saved SR
           `SPR_REG_ESR:    next_esr_r = reg_rb_r;
       endcase
    end
    default:
      ;
    endcase
end
 
//-----------------------------------------------------------------
// ALU inputs
//-----------------------------------------------------------------
 
// ALU operation selection
reg [3:0]  alu_func_r;
 
// ALU operands
reg [31:0] alu_input_a_r;
reg [31:0] alu_input_b_r;
reg        write_rd_r;
 
always @ *
begin
   alu_func_r     = `ALU_NONE;
   alu_input_a_r  = 32'b0;
   alu_input_b_r  = 32'b0;
   write_rd_r     = 1'b0;
 
   case (1'b1)
 
     inst_add_w: // l.add
     begin
       alu_func_r     = `ALU_ADD;
       alu_input_a_r  = reg_ra_r;
       alu_input_b_r  = reg_rb_r;
       write_rd_r     = 1'b1;
     end
 
     inst_addc_w: // l.addc
     begin
         alu_func_r     = `ALU_ADDC;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = reg_rb_r;
         write_rd_r     = 1'b1;
     end                     
 
     inst_and_w: // l.and
     begin
         alu_func_r     = `ALU_AND;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = reg_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_or_w: // l.or
     begin
         alu_func_r     = `ALU_OR;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = reg_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_sll_w: // l.sll
     begin
         alu_func_r     = `ALU_SHIFTL;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = shift_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_sw_ra: // l.sra
     begin
         alu_func_r     = `ALU_SHIRTR_ARITH;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = shift_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_srl_w: // l.srl
     begin
         alu_func_r     = `ALU_SHIFTR;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = shift_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_sub_w: // l.sub
     begin
         alu_func_r     = `ALU_SUB;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = reg_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_xor_w: // l.xor
     begin
         alu_func_r     = `ALU_XOR;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = reg_rb_r;
         write_rd_r     = 1'b1;
     end
 
     inst_mul_w,   // l.mul
     inst_mulu_w:  // l.mulu
     begin
         write_rd_r     = 1'b1;
     end     
 
     inst_addi_w: // l.addi
     begin
         alu_func_r     = `ALU_ADD;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = int32_r;
         write_rd_r     = 1'b1;
     end
 
     inst_andi_w: // l.andi
     begin
         alu_func_r     = `ALU_AND;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = uint32_r;
         write_rd_r     = 1'b1;
     end
 
     inst_jal_w: // l.jal
     begin
         alu_input_a_r  = next_pc_r;
         write_rd_r     = 1'b1;
     end
 
     inst_jalr_w: // l.jalr
     begin
         alu_input_a_r  = next_pc_r;
         write_rd_r     = 1'b1;
     end
 
     inst_mfspr_w: // l.mfspr
     begin
        case (mxspr_uint16_r)
           // SR - Supervision register
           `SPR_REG_SR:
           begin
               alu_input_a_r                = 32'b0;
               alu_input_a_r[`OR32_SR_F]    = next_sr_r[`OR32_SR_F];
               alu_input_a_r[`OR32_SR_CY]   = next_sr_r[`OR32_SR_CY];
               alu_input_a_r[`OR32_SR_IEE]  = next_sr_r[`OR32_SR_IEE];
               write_rd_r                   = 1'b1;
           end
 
           // EPCR - EPC Exception saved PC
           `SPR_REG_EPCR:
           begin
               alu_input_a_r  = r_epc;
               write_rd_r     = 1'b1;
           end
 
           // ESR - Exception saved SR
           `SPR_REG_ESR:
           begin
               alu_input_a_r                = 32'b0;
               alu_input_a_r[`OR32_SR_F]    = r_esr[`OR32_SR_F];
               alu_input_a_r[`OR32_SR_CY]   = r_esr[`OR32_SR_CY];
               alu_input_a_r[`OR32_SR_IEE]  = r_esr[`OR32_SR_IEE];           
               write_rd_r                   = 1'b1;
           end
           default:
              ;
        endcase
     end
 
     inst_movhi_w: // l.movhi
     begin
         alu_input_a_r  = {uint16_r,16'h0000};
         write_rd_r     = 1'b1;
     end
 
     inst_ori_w: // l.ori
     begin
         alu_func_r     = `ALU_OR;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = uint32_r;
         write_rd_r     = 1'b1;
     end
 
     inst_slli_w: // l.slli
     begin
         alu_func_r     = `ALU_SHIFTL;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = shift_imm_r;
         write_rd_r     = 1'b1;
     end
 
     inst_srai_w: // l.srai
     begin
         alu_func_r     = `ALU_SHIRTR_ARITH;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = shift_imm_r;
         write_rd_r     = 1'b1;
     end
 
     inst_srli_w: // l.srli
     begin
         alu_func_r     = `ALU_SHIFTR;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = shift_imm_r;
         write_rd_r     = 1'b1;
     end
 
     // l.lbs l.lhs l.lws l.lbz l.lhz l.lwz
     inst_lbs_w,
     inst_lhs_w,
     inst_lws_w,
     inst_lbz_w,
     inst_lhz_w,
     inst_lwz_w:
          write_rd_r    = 1'b1;
 
     inst_xori_w: // l.xori
     begin
         alu_func_r     = `ALU_XOR;
         alu_input_a_r  = reg_ra_r;
         alu_input_b_r  = int32_r;
         write_rd_r     = 1'b1;
     end
     default:
        ;     
   endcase
end
 
//-----------------------------------------------------------------
// Comparisons
//-----------------------------------------------------------------
 
reg [31:0] compare_a_r;
reg [31:0] compare_b_r;
always @ *
begin
    compare_a_r = reg_ra_r;
    compare_b_r = reg_rb_r;
 
    case (1'b1)
    inst_sfeqi_w,  // l.sfeqi
    inst_sfgesi_w, // l.sfgesi
    inst_sfgeui_w, // l.sfgeui
    inst_sfgtsi_w, // l.sfgtsi
    inst_sfgtui_w, // l.sfgtui
    inst_sflesi_w, // l.sflesi
    inst_sfleui_w, // l.sfleui
    inst_sfltsi_w, // l.sfltsi
    inst_sfltui_w, // l.sfltui
    inst_sfnei_w:  // l.sfnei
        compare_b_r = int32_r;
    default:
        ;    
    endcase
end
 
reg compare_equal_r;
reg compare_gts_r;
reg compare_gt_r;
reg compare_lts_r;
reg compare_lt_r;
always @ *
begin
    if (compare_a_r == compare_b_r)
        compare_equal_r = 1'b1;
    else
        compare_equal_r = 1'b0;
 
    compare_lts_r = less_than_signed(compare_a_r, compare_b_r);
 
    if (compare_a_r < compare_b_r)
        compare_lt_r = 1'b1;
    else
        compare_lt_r = 1'b0;        
 
    // Greater than (signed)
    compare_gts_r = ~(compare_lts_r | compare_equal_r);
 
    if (compare_a_r > compare_b_r)
        compare_gt_r = 1'b1;
    else
        compare_gt_r = 1'b0;
end
 
always @ *
begin
    compare_result_r = 1'b0;
 
    case (1'b1)
    inst_sfeq_w, // l.sfeq
    inst_sfeqi_w: // l.sfeqi
        compare_result_r = compare_equal_r;
 
    inst_sfges_w,  // l.sfges
    inst_sfgesi_w: // l.sfgesi
        compare_result_r = compare_gts_r | compare_equal_r;
 
    inst_sfgeu_w,  // l.sfgeu
    inst_sfgeui_w: // l.sfgeui
        compare_result_r = compare_gt_r | compare_equal_r;
 
    inst_sfgts_w,  // l.sfgts
    inst_sfgtsi_w: // l.sfgtsi
        compare_result_r = compare_gts_r;
 
    inst_sfgtu_w,  // l.sfgtu
    inst_sfgtui_w: // l.sfgtui
        compare_result_r = compare_gt_r;
 
    inst_sfles_w,  // l.sfles
    inst_sflesi_w: // l.sflesi
        compare_result_r = compare_lts_r | compare_equal_r;
 
    inst_sfleu_w,  // l.sfleu
    inst_sfleui_w: // l.sfleui
        compare_result_r = compare_lt_r | compare_equal_r;
 
    inst_sflts_w,  // l.sflts
    inst_sfltsi_w: // l.sfltsi
        compare_result_r = compare_lts_r;
 
    inst_sfltu_w,  // l.sfltu
    inst_sfltui_w: // l.sfltui
        compare_result_r = compare_lt_r;
 
    inst_sfne_w,  // l.sfne
    inst_sfnei_w: // l.sfnei
        compare_result_r = ~compare_equal_r;
 
    default:
        ;    
    endcase
end
 
//-----------------------------------------------------------------
// Branches
//-----------------------------------------------------------------
reg         branch_r;
reg         branch_link_r;
reg [31:0]  branch_target_r;
reg         branch_except_r;
 
always @ *
begin
 
    branch_r        = 1'b0;
    branch_link_r   = 1'b0;
    branch_except_r = 1'b0; 
 
    // Default branch target is relative to current PC
    branch_target_r = (r_pc + {target_int26_r[29:0],2'b00});    
 
    case (1'b1)
    inst_bf_w: // l.bf
        branch_r      = r_sr[`OR32_SR_F];
 
    inst_bnf_w: // l.bnf
        branch_r      = ~r_sr[`OR32_SR_F];
 
    inst_j_w: // l.j
        branch_r      = 1'b1;
 
    inst_jal_w: // l.jal
    begin
        // Write to REG_9_LR
        branch_link_r = 1'b1;
        branch_r      = 1'b1;
    end
 
    inst_jalr_w: // l.jalr
    begin
        // Write to REG_9_LR
        branch_link_r   = 1'b1;
        branch_r        = 1'b1;
        branch_target_r = reg_rb_r;
    end
 
    inst_jr_w: // l.jr
    begin
        branch_r        = 1'b1;
        branch_target_r = reg_rb_r;
    end
 
    inst_rfe_w: // l.rfe
    begin
        branch_r        = 1'b1;
        branch_target_r = r_epc;
    end
 
    inst_sys_w: // l.sys
    begin
        branch_r        = 1'b1;
        branch_except_r = 1'b1;
        branch_target_r = ISR_VECTOR + `VECTOR_SYSCALL;            
    end
 
    inst_trap_w: // l.trap
    begin
        branch_r        = 1'b1;
        branch_except_r = 1'b1;
        branch_target_r = ISR_VECTOR + `VECTOR_TRAP;
    end
 
    default:
        ;
    endcase
end
 
//-----------------------------------------------------------------
// Invalid instruction
//-----------------------------------------------------------------
reg invalid_inst_r;
 
always @ *
begin
    case (1'b1)
       inst_add_w, 
       inst_addc_w,
       inst_and_w,
       inst_or_w,
       inst_sll_w,
       inst_sw_ra,
       inst_srl_w,
       inst_sub_w,
       inst_xor_w,   
       inst_addi_w,
       inst_andi_w,
       inst_bf_w,
       inst_bnf_w,
       inst_j_w,
       inst_jal_w,
       inst_jalr_w,
       inst_jr_w,
       inst_lbs_w,
       inst_lhs_w,
       inst_lws_w,
       inst_lbz_w,
       inst_lhz_w,
       inst_lwz_w,
       inst_mfspr_w,
       inst_mtspr_w,
       inst_movhi_w,
       inst_nop_w,
       inst_ori_w,
       inst_rfe_w,
       inst_sb_w,
       inst_sh_w,
       inst_sw_w,
       inst_xori_w,
       inst_slli_w,
       inst_srai_w,
       inst_srli_w,
       inst_sfeq_w,
       inst_sfeqi_w,
       inst_sfges_w,
       inst_sfgesi_w,
       inst_sfgeu_w,
       inst_sfgeui_w,
       inst_sfgts_w,
       inst_sfgtsi_w,
       inst_sfgtu_w,
       inst_sfgtui_w,
       inst_sfles_w,
       inst_sflesi_w,
       inst_sfleu_w,
       inst_sfleui_w,
       inst_sflts_w,
       inst_sfltsi_w,
       inst_sfltu_w,
       inst_sfltui_w,
       inst_sfne_w,
       inst_sfnei_w,
       inst_sys_w,
       inst_trap_w:
          invalid_inst_r = 1'b0;
       default:
          invalid_inst_r = 1'b1;
    endcase
end
 
//-----------------------------------------------------------------
// Execute: ALU control
//-----------------------------------------------------------------
always @ (posedge clk_i or posedge rst_i)
begin
   if (rst_i == 1'b1)
   begin      
       r_e_alu_func         <= `ALU_NONE;
       r_e_alu_a            <= 32'h00000000;
       r_e_alu_b            <= 32'h00000000;
       r_e_rd               <= 5'b00000;
   end
   else
   begin           
           // Update ALU input flops
           r_e_alu_func         <= alu_func_r;
           r_e_alu_a            <= alu_input_a_r;
           r_e_alu_b            <= alu_input_b_r;
 
           // Branch and link (Rd = LR/R9)
           if (branch_link_r)
              r_e_rd            <= 5'd9;           
           // Instruction with register writeback
           else if (write_rd_r)
              r_e_rd            <= w_rd;
           else
              r_e_rd            <= 5'b0;
   end
end
 
//-----------------------------------------------------------------
// Execute: Branch / exceptions
//-----------------------------------------------------------------
always @ (posedge clk_i or posedge rst_i)
begin
   if (rst_i == 1'b1)
   begin
       r_pc                 <= BOOT_VECTOR + `VECTOR_RESET;
 
       // Status registers
       r_epc                <= 32'h00000000;
       r_sr                 <= 32'h00000000;
       r_esr                <= 32'h00000000;
 
       fault_o              <= 1'b0;
 
       r_nmi                <= 1'b0;
   end
   else
   begin
      // Record NMI in-case it can't be processed this cycle
      if (nmi_i)
          r_nmi             <= 1'b1;
 
       // Core disabled?
       if (~enable_i)
       begin
           // Reset
           r_pc                 <= BOOT_VECTOR + `VECTOR_RESET;
 
           // Status registers
           r_epc                <= 32'h00000000;
           r_sr                 <= 32'h00000000;
           r_esr                <= 32'h00000000;
 
           fault_o              <= 1'b0;
 
           r_nmi                <= 1'b0;
       end
       // Write-back?
       else if (w_write_en)
       begin
           // Update SR
           r_sr                 <= next_sr_r;
 
           // Exception: Instruction opcode not valid / supported, invalid PC
           if (invalid_inst_r || (r_pc[1:0] != 2'b00))
           begin
                // Save PC of next instruction
                r_epc       <= next_pc_r;
                r_esr       <= next_sr_r;
 
                // Disable further interrupts
                r_sr        <= 32'b0;
 
                // Set PC to exception vector
                if (invalid_inst_r)
                    r_pc    <= ISR_VECTOR + `VECTOR_ILLEGAL_INST;
                else
                    r_pc    <= ISR_VECTOR + `VECTOR_BUS_ERROR;
 
                fault_o     <= 1'b1;
           end       
           // Exception: Syscall / Break
           else if (branch_except_r)
           begin
                // Save PC of next instruction
                r_epc       <= next_pc_r;
                r_esr       <= next_sr_r;
 
                // Disable further interrupts
                r_sr        <= 32'b0;
 
                // Set PC to exception vector
                r_pc        <= branch_target_r;
 
    `ifdef CONF_CORE_DEBUG
               $display(" Exception 0x%08x", branch_target_r);
    `endif
           end
           // Non-maskable interrupt
           else if (nmi_i | r_nmi)
           begin
                r_nmi       <= 1'b0;
 
                // Save PC of next instruction
                if (branch_r)
                    r_epc <= branch_target_r;
                // Next expected PC (current PC + 4)
                else
                    r_epc <= next_pc_r;
 
                r_esr       <= next_sr_r;
 
                // Disable further interrupts
                r_sr        <= 32'b0;
 
                // Set PC to exception vector
                r_pc        <= ISR_VECTOR + `VECTOR_NMI;
 
    `ifdef CONF_CORE_DEBUG
               $display(" NMI 0x%08x", ISR_VECTOR + `VECTOR_NMI);
    `endif
           end       
           // External interrupt
           else if (intr_i && next_sr_r[`OR32_SR_IEE])
           begin
                // Save PC of next instruction & SR
                if (branch_r)
                    r_epc <= branch_target_r;
                // Next expected PC (current PC + 4)
                else
                    r_epc <= next_pc_r;
 
                r_esr       <= next_sr_r;
 
                // Disable further interrupts
                r_sr        <= 32'b0;
 
                // Set PC to external interrupt vector
                r_pc        <= ISR_VECTOR + `VECTOR_EXTINT;
 
    `ifdef CONF_CORE_DEBUG
               $display(" External Interrupt 0x%08x", ISR_VECTOR + `VECTOR_EXTINT);
    `endif
           end        
           // Branch (l.bf, l.bnf, l.j, l.jal, l.jr, l.jalr, l.rfe)
           else if (branch_r)
           begin
                // Perform branch
                r_pc        <= branch_target_r;
 
    `ifdef CONF_CORE_DEBUG
               $display(" Branch to 0x%08x", branch_target_r);
    `endif
           end
           // Non branch
           else
           begin
                // Update EPC / ESR which may have been updated
                // by an MTSPR write
                r_pc           <= next_pc_r;
                r_epc          <= next_epc_r;
                r_esr          <= next_esr_r;
           end
      end
   end
end
 
//-------------------------------------------------------------------
// Load result
//-------------------------------------------------------------------
always @ *
begin
    r_load_result   = 32'h00000000;
 
    case (1'b1)
 
        inst_lbs_w, // l.lbs
        inst_lbz_w: // l.lbz
        begin
            case (mem_offset)
                2'b00 :   r_load_result[7:0] = mem_dat_i[31:24];
                2'b01 :   r_load_result[7:0] = mem_dat_i[23:16];
                2'b10 :   r_load_result[7:0] = mem_dat_i[15:8];
                2'b11 :   r_load_result[7:0] = mem_dat_i[7:0];
                default : ;
            endcase
 
            // Sign extend LB
            if (inst_lbs_w && r_load_result[7])
                r_load_result[31:8] = 24'hFFFFFF;
        end
 
        inst_lhs_w, // l.lhs
        inst_lhz_w: // l.lhz
        begin
            case (mem_offset)
                2'b00 :   r_load_result[15:0] = mem_dat_i[31:16];
                2'b10 :   r_load_result[15:0] = mem_dat_i[15:0];
                default : ;                
            endcase
 
            // Sign extend LH
            if (inst_lhs_w && r_load_result[15])
                r_load_result[31:16] = 16'hFFFF;
        end
 
        // l.lwz l.lws
        default :
            r_load_result   = mem_dat_i;
    endcase  
end
 
//-----------------------------------------------------------------
// Execute: Misc operations
//-----------------------------------------------------------------
always @ (posedge clk_i or posedge rst_i)
begin
   if (rst_i == 1'b1)
   begin
       break_o              <= 1'b0;
   end
   else
   begin
       break_o              <= 1'b0;
 
       case (1'b1)
       inst_trap_w: // l.trap
            break_o         <= 1'b1;
       default:
          ;
      endcase
   end
end
 
//-----------------------------------------------------------------
// Execute: NOP (simulation) operations
//-----------------------------------------------------------------
`ifdef SIMULATION
    always @ (posedge clk_i or posedge rst_i)
    begin
       if (rst_i == 1'b1)
       begin
    `ifdef SIM_EXT_PUTC
          r_putc                <= 8'b0;
    `endif
       end
       else
       begin
    `ifdef SIM_EXT_PUTC
          r_putc                <= 8'b0;
    `endif   
          if (inst_nop_w && state == STATE_EXEC)
          begin
                case (uint16_r)
                // NOP_PUTC
                16'h0004:
                begin
  `ifdef SIM_EXT_PUTC
                  r_putc  <= reg_ra_r[7:0];
  `else    
                  $write("%c", reg_ra_r[7:0]);
  `endif              
                end
                // NOP
                16'h0000: ;
                endcase
          end
       end
    end
`endif
 
`include "altor32_funcs.v"
 
//-------------------------------------------------------------------
// Hooks for debug
//-------------------------------------------------------------------
`ifdef verilator
   function [31:0] get_opcode_ex;
      // verilator public
      get_opcode_ex = (state == STATE_EXEC) ? r_opcode : `OPCODE_INST_BUBBLE;
   endfunction
   function [31:0] get_pc_ex;
      // verilator public
      get_pc_ex = r_pc;
   endfunction   
   function [7:0] get_putc;
      // verilator public
   `ifdef SIM_EXT_PUTC
      get_putc = r_putc;
   `else
      get_putc = 8'b0;
   `endif      
   endfunction
   function [0:0] get_reg_valid;
      // verilator public
      get_reg_valid = (state == STATE_EXEC) ? 1'b1 : 1'b0;
   endfunction
   function [4:0] get_reg_ra;
      // verilator public
      get_reg_ra = w_ra;
   endfunction
   function [31:0] get_reg_ra_value;
      // verilator public
      get_reg_ra_value = w_reg_ra;
   endfunction
   function [4:0] get_reg_rb;
      // verilator public
      get_reg_rb = w_rb;
   endfunction   
   function [31:0] get_reg_rb_value;
      // verilator public
      get_reg_rb_value = w_reg_rb;
   endfunction
`endif
 
endmodule