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

//                                                              //

//  Execute stage of Amber 25 Core                              //

//                                                              //

//  This file is part of the Amber project                      //

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

//                                                              //

//  Description                                                 //

//  Executes instructions. Instantiates the register file, ALU  //

//  multiplication unit and barrel shifter. This stage is       //

//  relitively simple. All the complex stuff is done in the     //

//  decode stage.                                               //

//                                                              //

//  Author(s):                                                  //

//      - Conor Santifort, csantifort.amber@gmail.com           //

//                                                              //

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

//                                                              //

// Copyright (C) 2011 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                     //

//                                                              //

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

module a25_execute (

input                       i_clk,

input                       i_core_stall,               // stall all stages of the Amber core at the same time

input                       i_mem_stall,                // data memory access stalls

output                      o_exec_stall,               // stall the core pipeline

input       [31:0]          i_wb_read_data,             // data reads

input                       i_wb_read_data_valid,       // read data is valid

input       [10:0]          i_wb_load_rd,               // Rd for data reads

input       [31:0]          i_copro_read_data,          // From Co-Processor, to either Register 

                                                        // or Memory

input                       i_decode_iaccess,           // Indicates an instruction access

input                       i_decode_daccess,           // Indicates a data access

input       [7:0]           i_decode_load_rd,           // The destination register for a load instruction

output reg  [31:0]          o_copro_write_data = 'd0,

output reg  [31:0]          o_write_data = 'd0,

output reg  [31:0]          o_iaddress = 32'hdead_dead,

output      [31:0]          o_iaddress_nxt,             // un-registered version of address to the 

                                                        // cache rams address ports

output reg                  o_iaddress_valid = 'd0,     // High when instruction address is valid

output reg  [31:0]          o_daddress = 32'h0,         // Address to data cache

output      [31:0]          o_daddress_nxt,             // un-registered version of address to the 

                                                        // cache rams address ports

output reg                  o_daddress_valid = 'd0,     // High when data address is valid

output reg                  o_adex = 'd0,               // Address Exception

output reg                  o_priviledged = 'd0,        // Priviledged access

output reg                  o_exclusive = 'd0,          // swap access

output reg                  o_write_enable = 'd0,

output reg  [3:0]           o_byte_enable = 'd0,

output reg  [8:0]           o_exec_load_rd = 'd0,       // The destination register for a load instruction

output      [31:0]          o_status_bits,              // Full PC will all status bits, but PC part zero'ed out

output                      o_multiply_done,

// --------------------------------------------------

// Control signals from Instruction Decode stage

// --------------------------------------------------

input      [1:0]            i_status_bits_mode,

input                       i_status_bits_irq_mask,

input                       i_status_bits_firq_mask,

input      [31:0]           i_imm32,

input      [4:0]            i_imm_shift_amount,

input                       i_shift_imm_zero,

input      [3:0]            i_condition,

input                       i_decode_exclusive,       // swap access

input      [3:0]            i_rm_sel,

input      [3:0]            i_rs_sel,

input      [3:0]            i_rn_sel,

input      [1:0]            i_barrel_shift_amount_sel,

input      [1:0]            i_barrel_shift_data_sel,

input      [1:0]            i_barrel_shift_function,

input      [8:0]            i_alu_function,

input      [1:0]            i_multiply_function,

input      [2:0]            i_interrupt_vector_sel,

input      [3:0]            i_iaddress_sel,

input      [3:0]            i_daddress_sel,

input      [2:0]            i_pc_sel,

input      [1:0]            i_byte_enable_sel,

input      [2:0]            i_status_bits_sel,

input      [2:0]            i_reg_write_sel,

input                       i_user_mode_regs_store_nxt,

input                       i_firq_not_user_mode,

input                       i_use_carry_in,         // e.g. add with carry instruction

input                       i_write_data_wen,

input                       i_base_address_wen,     // save LDM base address register, 

                                                    // in case of data abort

input                       i_pc_wen,

input      [14:0]           i_reg_bank_wen,

input                       i_status_bits_flags_wen,

input                       i_status_bits_mode_wen,

input                       i_status_bits_irq_mask_wen,

input                       i_status_bits_firq_mask_wen,

input                       i_copro_write_data_wen,

input                       i_conflict,

input                       i_rn_use_read,

input                       i_rm_use_read,

input                       i_rs_use_read,

input                       i_rd_use_read

);

`include "a25_localparams.vh"

`include "a25_functions.vh"

// ========================================================

// Internal signals

// ========================================================

wire [31:0]         write_data_nxt;

wire [3:0]          byte_enable_nxt;

wire [31:0]         pc_plus4;

wire [31:0]         pc_minus4;

wire [31:0]         daddress_plus4;

wire [31:0]         alu_plus4;

wire [31:0]         rn_plus4;

wire [31:0]         alu_out;

wire [3:0]          alu_flags;

wire [31:0]         rm;

wire [31:0]         rs;

wire [31:0]         rd;

wire [31:0]         rn;

wire [31:0]         reg_bank_rn;

wire [31:0]         reg_bank_rm;

wire [31:0]         reg_bank_rs;

wire [31:0]         reg_bank_rd;

wire [31:0]         pc;

wire [31:0]         pc_nxt;

wire [31:0]         interrupt_vector;

wire [7:0]          shift_amount;

wire [31:0]         barrel_shift_in;

wire [31:0]         barrel_shift_out;

wire                barrel_shift_carry;

wire                barrel_shift_stall;

wire [3:0]          status_bits_flags_nxt;

reg  [3:0]          status_bits_flags = 'd0;

wire [1:0]          status_bits_mode_nxt;

reg  [1:0]          status_bits_mode = SVC;

                    // one-hot encoded rs select

wire [3:0]          status_bits_mode_rds_oh_nxt;

reg  [3:0]          status_bits_mode_rds_oh = 1'd1 << OH_SVC;

wire                status_bits_mode_rds_oh_update;

wire                status_bits_irq_mask_nxt;

reg                 status_bits_irq_mask = 1'd1;

wire                status_bits_firq_mask_nxt;

reg                 status_bits_firq_mask = 1'd1;

wire [8:0]          exec_load_rd_nxt;

wire                execute;                    // high when condition execution is true

wire [31:0]         reg_write_nxt;

wire                pc_wen;

wire [14:0]         reg_bank_wen;

wire [31:0]         multiply_out;

wire [1:0]          multiply_flags;

reg  [31:0]         base_address = 'd0;             // Saves base address during LDM instruction in 

                                                    // case of data abort

wire [31:0]         read_data_filtered1;

wire [31:0]         read_data_filtered;

wire [31:0]         read_data_filtered_c;

reg  [31:0]         read_data_filtered_r = 'd0;

reg  [3:0]          load_rd_r = 'd0;

wire [3:0]          load_rd_c;

wire                write_enable_nxt;

wire                daddress_valid_nxt;

wire                iaddress_valid_nxt;

wire                priviledged_nxt;

wire                priviledged_update;

wire                iaddress_update;

wire                daddress_update;

wire                base_address_update;

wire                write_data_update;

wire                copro_write_data_update;

wire                byte_enable_update;

wire                exec_load_rd_update;

wire                write_enable_update;

wire                exclusive_update;

wire                status_bits_flags_update;

wire                status_bits_mode_update;

wire                status_bits_irq_mask_update;

wire                status_bits_firq_mask_update;

wire [31:0]         alu_out_pc_filtered;

wire                adex_nxt;

wire [31:0]         save_int_pc;

wire [31:0]         save_int_pc_m4;

wire                ldm_flags;

wire                ldm_status_bits;

wire                carry_in;

// ========================================================

// Status Bits in PC register

// ========================================================

wire [1:0] status_bits_mode_out;

assign status_bits_mode_out = (i_status_bits_mode_wen && i_status_bits_sel == 3'd1 && !ldm_status_bits) ?

                                    alu_out[1:0] : status_bits_mode ;

assign o_status_bits = {   status_bits_flags,           // 31:28

                           status_bits_irq_mask,        // 7

                           status_bits_firq_mask,       // 6

                           24'd0,

                           status_bits_mode_out };      // 1:0 = mode

// ========================================================

// Status Bits Select

// ========================================================

assign ldm_flags                 = i_wb_read_data_valid & ~i_mem_stall & i_wb_load_rd[8];

assign ldm_status_bits           = i_wb_read_data_valid & ~i_mem_stall & i_wb_load_rd[7];

assign status_bits_flags_nxt     = ldm_flags                 ? read_data_filtered[31:28]           :

                                   i_status_bits_sel == 3'd0 ? alu_flags                           :

                                   i_status_bits_sel == 3'd1 ? alu_out          [31:28]            :

                                   i_status_bits_sel == 3'd3 ? i_copro_read_data[31:28]            :

                                   // 4 = update flags after a multiply operation

                                   i_status_bits_sel == 3'd4 ? { multiply_flags, status_bits_flags[1:0] } :

                                   // regops that do not change the overflow flag

                                   i_status_bits_sel == 3'd5 ? { alu_flags[3:1], status_bits_flags[0] } :

                                                               4'b1111 ;

assign status_bits_mode_nxt      = ldm_status_bits           ? read_data_filtered [1:0] :

                                   i_status_bits_sel == 3'd0 ? i_status_bits_mode       :

                                   i_status_bits_sel == 3'd5 ? i_status_bits_mode       :

                                   i_status_bits_sel == 3'd1 ? alu_out            [1:0] :

                                                               i_copro_read_data  [1:0] ;

// Used for the Rds output of register_bank - this special version of

// status_bits_mode speeds up the critical path from status_bits_mode through the

// register_bank, barrel_shifter and alu. It moves a mux needed for the

// i_user_mode_regs_store_nxt signal back into the previous stage -

// so its really part of the decode stage even though the logic is right here

// In addition the signal is one-hot encoded to further speed up the logic

assign status_bits_mode_rds_oh_nxt    = i_user_mode_regs_store_nxt ? 1'd1 << OH_USR                            :

                                        status_bits_mode_update    ? oh_status_bits_mode(status_bits_mode_nxt) :

                                                                     oh_status_bits_mode(status_bits_mode)     ;

assign status_bits_irq_mask_nxt  = ldm_status_bits           ? read_data_filtered     [27] :

                                   i_status_bits_sel == 3'd0 ? i_status_bits_irq_mask      :

                                   i_status_bits_sel == 3'd5 ? i_status_bits_irq_mask      :

                                   i_status_bits_sel == 3'd1 ? alu_out                [27] :

                                                               i_copro_read_data      [27] ;

assign status_bits_firq_mask_nxt = ldm_status_bits           ? read_data_filtered     [26] :

                                   i_status_bits_sel == 3'd0 ? i_status_bits_firq_mask     :

                                   i_status_bits_sel == 3'd5 ? i_status_bits_firq_mask     :

                                   i_status_bits_sel == 3'd1 ? alu_out                [26] :

                                                               i_copro_read_data      [26] ;

// ========================================================

// Adders

// ========================================================

assign pc_plus4       = pc         + 32'd4;

assign pc_minus4      = pc         - 32'd4;

assign daddress_plus4 = o_daddress + 32'd4;

assign alu_plus4      = alu_out    + 32'd4;

assign rn_plus4       = rn         + 32'd4;

// ========================================================

// Barrel Shift Amount Select

// ========================================================

// An immediate shift value of 0 is translated into 32

assign shift_amount = i_barrel_shift_amount_sel == 2'd0 ? 8'd0                         :

                      i_barrel_shift_amount_sel == 2'd1 ? rs[7:0]                      :

                                                          {3'd0, i_imm_shift_amount  } ;

// ========================================================

// Barrel Shift Data Select

// ========================================================

assign barrel_shift_in = i_barrel_shift_data_sel == 2'd0 ? i_imm32 : rm ;

// ========================================================

// Interrupt vector Select

// ========================================================

assign interrupt_vector = // Reset vector

                          (i_interrupt_vector_sel == 3'd0) ? 32'h00000000 :

                          // Data abort interrupt vector                 

                          (i_interrupt_vector_sel == 3'd1) ? 32'h00000010 :

                          // Fast interrupt vector  

                          (i_interrupt_vector_sel == 3'd2) ? 32'h0000001c :

                          // Regular interrupt vector

                          (i_interrupt_vector_sel == 3'd3) ? 32'h00000018 :

                          // Prefetch abort interrupt vector

                          (i_interrupt_vector_sel == 3'd5) ? 32'h0000000c :

                          // Undefined instruction interrupt vector

                          (i_interrupt_vector_sel == 3'd6) ? 32'h00000004 :

                          // Software (SWI) interrupt vector

                          (i_interrupt_vector_sel == 3'd7) ? 32'h00000008 :

                          // Default is the address exception interrupt

                                                             32'h00000014 ;

// ========================================================

// Address Select

// ========================================================

assign pc_dmem_wen    = i_wb_read_data_valid & ~i_mem_stall & i_wb_load_rd[3:0] == 4'd15;

// If rd is the pc, then seperate the address bits from the status bits for

// generating the next address to fetch

assign alu_out_pc_filtered = pc_wen && i_pc_sel == 3'd1 ? pcf(alu_out) : alu_out;

// if current instruction does not execute because it does not meet the condition

// then address advances to next instruction

assign o_iaddress_nxt = (pc_dmem_wen)            ? pcf(read_data_filtered) :

                        (!execute)               ? pc_plus4                :

                        (i_iaddress_sel == 4'd0) ? pc_plus4                :

                        (i_iaddress_sel == 4'd1) ? alu_out_pc_filtered     :

                        (i_iaddress_sel == 4'd2) ? interrupt_vector        :

                                                   pc                      ;

// if current instruction does not execute because it does not meet the condition

// then address advances to next instruction

assign o_daddress_nxt = (i_daddress_sel == 4'd1) ? alu_out_pc_filtered   :

                        (i_daddress_sel == 4'd2) ? interrupt_vector      :

                        (i_daddress_sel == 4'd4) ? rn                    :

                        (i_daddress_sel == 4'd5) ? daddress_plus4        :  // MTRANS address incrementer

                        (i_daddress_sel == 4'd6) ? alu_plus4             :  // MTRANS decrement after

                                                   rn_plus4              ;  // MTRANS increment before

// Data accesses use 32-bit address space, but instruction

// accesses are restricted to 26 bit space

assign adex_nxt      = |o_iaddress_nxt[31:26] && i_decode_iaccess;

// ========================================================

// Filter Read Data

// ========================================================

// mem_load_rd[10:9]-> shift ROR bytes

// mem_load_rd[8]   -> load flags with PC

// mem_load_rd[7]   -> load status bits with PC

// mem_load_rd[6:5] -> Write into this Mode registers

// mem_load_rd[4]   -> zero_extend byte

// mem_load_rd[3:0] -> Destination Register 

assign read_data_filtered1 = i_wb_load_rd[10:9] == 2'd0 ? i_wb_read_data                                :

                             i_wb_load_rd[10:9] == 2'd1 ? {i_wb_read_data[7:0],  i_wb_read_data[31:8]}  :

                             i_wb_load_rd[10:9] == 2'd2 ? {i_wb_read_data[15:0], i_wb_read_data[31:16]} :

                                                          {i_wb_read_data[23:0], i_wb_read_data[31:24]} ;

assign read_data_filtered  = i_wb_load_rd[4] ? {24'd0, read_data_filtered1[7:0]} : read_data_filtered1 ;

// ========================================================

// Program Counter Select

// ========================================================

// If current instruction does not execute because it does not meet the condition

// then PC advances to next instruction

assign pc_nxt = (!execute)       ? pc_plus4                :

                i_pc_sel == 3'd0 ? pc_plus4                :

                i_pc_sel == 3'd1 ? alu_out                 :

                i_pc_sel == 3'd2 ? interrupt_vector        :

                i_pc_sel == 3'd3 ? pcf(read_data_filtered) :

                                   pc_minus4               ;

// ========================================================

// Register Write Select

// ========================================================

assign save_int_pc    = { status_bits_flags,

                          status_bits_irq_mask,

                          status_bits_firq_mask,

                          pc[25:2],

                          status_bits_mode      };

assign save_int_pc_m4 = { status_bits_flags,

                          status_bits_irq_mask,

                          status_bits_firq_mask,

                          pc_minus4[25:2],

                          status_bits_mode      };

assign reg_write_nxt = i_reg_write_sel == 3'd0 ? alu_out               :

                       // save pc to lr on an interrupt                    

                       i_reg_write_sel == 3'd1 ? save_int_pc_m4        :

                       // to update Rd at the end of Multiplication

                       i_reg_write_sel == 3'd2 ? multiply_out          :

                       i_reg_write_sel == 3'd3 ? o_status_bits         :

                       i_reg_write_sel == 3'd5 ? i_copro_read_data     :  // mrc

                       i_reg_write_sel == 3'd6 ? base_address          :

                                                 save_int_pc           ;

// ========================================================

// Byte Enable Select

// ========================================================

assign byte_enable_nxt = i_byte_enable_sel == 2'd0   ? 4'b1111 :  // word write

                         i_byte_enable_sel == 2'd2   ?            // halfword write

                         ( o_daddress_nxt[1] == 1'd0 ? 4'b0011 :

                                                       4'b1100  ) :

                         o_daddress_nxt[1:0] == 2'd0 ? 4'b0001 :  // byte write

                         o_daddress_nxt[1:0] == 2'd1 ? 4'b0010 :

                         o_daddress_nxt[1:0] == 2'd2 ? 4'b0100 :

                                                       4'b1000 ;

// ========================================================

// Write Data Select

// ========================================================

assign write_data_nxt = i_byte_enable_sel == 2'd0 ? rd            :

                                                    {4{rd[ 7:0]}} ;

// ========================================================

// Conditional Execution

// ========================================================

assign execute = conditional_execute ( i_condition, status_bits_flags );

// allow the PC to increment to the next instruction when current

// instruction does not execute

assign pc_wen       = (i_pc_wen || !execute) && !i_conflict;

// only update register bank if current instruction executes

assign reg_bank_wen = {{15{execute}} & i_reg_bank_wen};

// ========================================================

// Priviledged output flag

// ========================================================

// Need to look at status_bits_mode_nxt so switch to priviledged mode

// at the same time as assert interrupt vector address

assign priviledged_nxt  = ( i_status_bits_mode_wen ? status_bits_mode_nxt : status_bits_mode ) != USR ;

// ========================================================

// Write Enable

// ========================================================

// This must be de-asserted when execute is fault

assign write_enable_nxt = execute && i_write_data_wen;

// ========================================================

// Address Valid

// ========================================================

assign daddress_valid_nxt = execute && i_decode_daccess && !i_core_stall;

// For some multi-cycle instructions, the stream of instrution

// reads can be paused. However if the instruction does not execute

// then the read stream must not be interrupted.

assign iaddress_valid_nxt = i_decode_iaccess || !execute;

// ========================================================

// Use read value from data memory instead of from register

// ========================================================

assign rn = i_rn_use_read && i_rn_sel == load_rd_c ? read_data_filtered_c : reg_bank_rn;

assign rm = i_rm_use_read && i_rm_sel == load_rd_c ? read_data_filtered_c : reg_bank_rm;

assign rs = i_rs_use_read && i_rs_sel == load_rd_c ? read_data_filtered_c : reg_bank_rs;

assign rd = i_rd_use_read && i_rs_sel == load_rd_c ? read_data_filtered_c : reg_bank_rd;

always@( posedge i_clk )

    if ( i_wb_read_data_valid )

        begin

        read_data_filtered_r <= read_data_filtered;

        load_rd_r            <= i_wb_load_rd[3:0];

        end

assign read_data_filtered_c = i_wb_read_data_valid ? read_data_filtered : read_data_filtered_r;

assign load_rd_c            = i_wb_read_data_valid ? i_wb_load_rd[3:0]  : load_rd_r;

// ========================================================

// Set mode for the destination registers of a mem read

// ========================================================

// The mode is either user mode, or the current mode

assign  exec_load_rd_nxt   = { i_decode_load_rd[7:6],

                               i_decode_load_rd[5] ? USR : status_bits_mode,  // 1 bit -> 2 bits

                               i_decode_load_rd[4:0] };

// ========================================================

// Register Update

// ========================================================

assign o_exec_stall                    = barrel_shift_stall;

assign daddress_update                 = !i_core_stall;

assign exec_load_rd_update             = !i_core_stall && execute;

assign priviledged_update              = !i_core_stall;

assign exclusive_update                = !i_core_stall && execute;

assign write_enable_update             = !i_core_stall;

assign write_data_update               = !i_core_stall && execute && i_write_data_wen;

assign byte_enable_update              = !i_core_stall && execute && i_write_data_wen;

assign iaddress_update                 = pc_dmem_wen || (!i_core_stall && !i_conflict);

assign copro_write_data_update         = !i_core_stall && execute && i_copro_write_data_wen;

assign base_address_update             = !i_core_stall && execute && i_base_address_wen;

assign status_bits_flags_update        = ldm_flags       || (!i_core_stall && execute && i_status_bits_flags_wen);

assign status_bits_mode_update         = ldm_status_bits || (!i_core_stall && execute && i_status_bits_mode_wen);

assign status_bits_mode_rds_oh_update  = !i_core_stall;

assign status_bits_irq_mask_update     = ldm_status_bits || (!i_core_stall && execute && i_status_bits_irq_mask_wen);

assign status_bits_firq_mask_update    = ldm_status_bits || (!i_core_stall && execute && i_status_bits_firq_mask_wen);

always @( posedge i_clk )

    begin

    o_daddress              <= daddress_update                ? o_daddress_nxt               : o_daddress;

    o_daddress_valid        <= daddress_update                ? daddress_valid_nxt           : o_daddress_valid;

    o_exec_load_rd          <= exec_load_rd_update            ? exec_load_rd_nxt             : o_exec_load_rd;

    o_priviledged           <= priviledged_update             ? priviledged_nxt              : o_priviledged;

    o_exclusive             <= exclusive_update               ? i_decode_exclusive           : o_exclusive;

    o_write_enable          <= write_enable_update            ? write_enable_nxt             : o_write_enable;

    o_write_data            <= write_data_update              ? write_data_nxt               : o_write_data;

    o_byte_enable           <= byte_enable_update             ? byte_enable_nxt              : o_byte_enable;

    o_iaddress              <= iaddress_update                ? o_iaddress_nxt               : o_iaddress;

    o_iaddress_valid        <= iaddress_update                ? iaddress_valid_nxt           : o_iaddress_valid;

    o_adex                  <= iaddress_update                ? adex_nxt                     : o_adex;

    o_copro_write_data      <= copro_write_data_update        ? write_data_nxt               : o_copro_write_data;

    base_address            <= base_address_update            ? rn                           : base_address;

    status_bits_flags       <= status_bits_flags_update       ? status_bits_flags_nxt        : status_bits_flags;

    status_bits_mode        <= status_bits_mode_update        ? status_bits_mode_nxt         : status_bits_mode;

    status_bits_mode_rds_oh <= status_bits_mode_rds_oh_update ? status_bits_mode_rds_oh_nxt  : status_bits_mode_rds_oh;

    status_bits_irq_mask    <= status_bits_irq_mask_update    ? status_bits_irq_mask_nxt     : status_bits_irq_mask;

    status_bits_firq_mask   <= status_bits_firq_mask_update   ? status_bits_firq_mask_nxt    : status_bits_firq_mask;

    end

// ========================================================

// Instantiate Barrel Shift

// ========================================================

assign carry_in = i_use_carry_in ? status_bits_flags[1] : 1'd0;

a25_barrel_shift u_barrel_shift  (

    .i_clk            ( i_clk                     ),

    .i_in             ( barrel_shift_in           ),

    .i_carry_in       ( carry_in                  ),

    .i_shift_amount   ( shift_amount              ),

    .i_shift_imm_zero ( i_shift_imm_zero          ),

    .i_function       ( i_barrel_shift_function   ),

    .o_out            ( barrel_shift_out          ),

    .o_carry_out      ( barrel_shift_carry        ),

    .o_stall          ( barrel_shift_stall        )

);

// ========================================================

// Instantiate ALU

// ========================================================

a25_alu u_alu (

    .i_a_in                 ( rn                    ),

    .i_b_in                 ( barrel_shift_out      ),

    .i_barrel_shift_carry   ( barrel_shift_carry    ),

    .i_status_bits_carry    ( status_bits_flags[1]  ),

    .i_function             ( i_alu_function        ),

    .o_out                  ( alu_out               ),

    .o_flags                ( alu_flags             )

);

// ========================================================

// Instantiate Booth 64-bit Multiplier-Accumulator

// ========================================================

a25_multiply u_multiply (

    .i_clk          ( i_clk                 ),

    .i_core_stall   ( i_core_stall          ),

    .i_a_in         ( rs                    ),

    .i_b_in         ( rm                    ),

    .i_function     ( i_multiply_function   ),

    .i_execute      ( execute               ),

    .o_out          ( multiply_out          ),

    .o_flags        ( multiply_flags        ),  // [1] = N, [0] = Z

    .o_done         ( o_multiply_done       )

);

// ========================================================

// Instantiate Register Bank

// ========================================================

a25_register_bank u_register_bank(

    .i_clk                   ( i_clk                     ),

    .i_core_stall            ( i_core_stall              ),

    .i_mem_stall             ( i_mem_stall               ),

    .i_rm_sel                ( i_rm_sel                  ),

    .i_rs_sel                ( i_rs_sel                  ),

    .i_rn_sel                ( i_rn_sel                  ),

    .i_pc_wen                ( pc_wen                    ),

    .i_reg_bank_wen          ( reg_bank_wen              ),

    .i_pc                    ( pc_nxt[25:2]              ),

    .i_reg                   ( reg_write_nxt             ),

    .i_mode_idec             ( i_status_bits_mode        ),

    .i_mode_exec             ( status_bits_mode          ),