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/* ****************************************************************************

  This Source Code Form is subject to the terms of the

  Open Hardware Description License, v. 1.0. If a copy

  of the OHDL was not distributed with this file, You

  can obtain one at http://juliusbaxter.net/ohdl/ohdl.txt

  Description: Cappuccino decode to execute module.

  - Decode to execute stage signal passing.

  - Branches are resolved (in decode stage).

  - Hazards that can not be resolved by bypassing are detected and

    bubbles are inserted on such conditions.

  Generate valid signal when stage is done.

  Copyright (C) 2012 Julius Baxter <juliusbaxter@gmail.com>

  Copyright (C) 2013 Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>

***************************************************************************** */

`include "mor1kx-defines.v"

module mor1kx_decode_execute_cappuccino

  #(

    parameter OPTION_OPERAND_WIDTH = 32,

    parameter OPTION_RESET_PC = {{(OPTION_OPERAND_WIDTH-13){1'b0}},

                                 `OR1K_RESET_VECTOR,8'd0},

    parameter OPTION_RF_ADDR_WIDTH = 5,

    parameter FEATURE_SYSCALL = "ENABLED",

    parameter FEATURE_TRAP = "ENABLED",

    parameter FEATURE_DELAY_SLOT = "ENABLED",

    parameter FEATURE_MULTIPLIER = "THREESTAGE",

    parameter FEATURE_INBUILT_CHECKERS = "ENABLED"

    )

   (

    input                                 clk,

    input                                 rst,

    // pipeline control signal in

    input                                 padv_i,

    input [OPTION_OPERAND_WIDTH-1:0]       pc_decode_i,

    // input from register file

    input [OPTION_OPERAND_WIDTH-1:0]       decode_rfb_i,

    input [OPTION_OPERAND_WIDTH-1:0]       execute_rfb_i,

    // Branch prediction signals

    input                                 predicted_flag_i,

    output reg                            execute_predicted_flag_o,

    // The target pc that should be used in case of branch misprediction

    output reg [OPTION_OPERAND_WIDTH-1:0] execute_mispredict_target_o,

    input                                 pipeline_flush_i,

    // ALU related inputs from decode

    input [`OR1K_ALU_OPC_WIDTH-1:0]        decode_opc_alu_i,

    input [`OR1K_ALU_OPC_WIDTH-1:0]        decode_opc_alu_secondary_i,

    input [`OR1K_IMM_WIDTH-1:0]    decode_imm16_i,

    input [OPTION_OPERAND_WIDTH-1:0]       decode_immediate_i,

    input                                 decode_immediate_sel_i,

    //  ALU related outputs to execute

    output reg [`OR1K_ALU_OPC_WIDTH-1:0]  execute_opc_alu_o,

    output reg [`OR1K_ALU_OPC_WIDTH-1:0]  execute_opc_alu_secondary_o,

    output reg [`OR1K_IMM_WIDTH-1:0]       execute_imm16_o,

    output reg [OPTION_OPERAND_WIDTH-1:0] execute_immediate_o,

    output reg                            execute_immediate_sel_o,

    // Adder control logic from decode

    input                                 decode_adder_do_sub_i,

    input                                 decode_adder_do_carry_i,

    // Adder control logic to execute

    output reg                            execute_adder_do_sub_o,

    output reg                            execute_adder_do_carry_o,

    // Upper 10 bits of immediate for jumps and branches

    input [9:0]                    decode_immjbr_upper_i,

    output reg [9:0]                       execute_immjbr_upper_o,

    // GPR numbers

    output reg [OPTION_RF_ADDR_WIDTH-1:0] execute_rfd_adr_o,

    input [OPTION_RF_ADDR_WIDTH-1:0]       decode_rfd_adr_i,

    input [OPTION_RF_ADDR_WIDTH-1:0]       decode_rfa_adr_i,

    input [OPTION_RF_ADDR_WIDTH-1:0]       decode_rfb_adr_i,

    input [OPTION_RF_ADDR_WIDTH-1:0]       ctrl_rfd_adr_i,

    input                                 ctrl_op_lsu_load_i,

    input                                 ctrl_op_mfspr_i,

    input                                 ctrl_op_mul_i,

    // Control signal inputs from decode stage

    input                                 decode_rf_wb_i,

    input                                 decode_op_alu_i,

    input                                 decode_op_setflag_i,

    input                                 decode_op_jbr_i,

    input                                 decode_op_jr_i,

    input                                 decode_op_jal_i,

    input                                 decode_op_bf_i,

    input                                 decode_op_bnf_i,

    input                                 decode_op_brcond_i,

    input                                 decode_op_branch_i,

    input                                 decode_op_lsu_load_i,

    input                                 decode_op_lsu_store_i,

    input                                 decode_op_lsu_atomic_i,

    input [1:0]                    decode_lsu_length_i,

    input                                 decode_lsu_zext_i,

    input                                 decode_op_mfspr_i,

    input                                 decode_op_mtspr_i,

    input                                 decode_op_rfe_i,

    input                                 decode_op_add_i,

    input                                 decode_op_mul_i,

    input                                 decode_op_mul_signed_i,

    input                                 decode_op_mul_unsigned_i,

    input                                 decode_op_div_i,

    input                                 decode_op_div_signed_i,

    input                                 decode_op_div_unsigned_i,

    input                                 decode_op_shift_i,

    input                                 decode_op_ffl1_i,

    input                                 decode_op_movhi_i,

    input [`OR1K_OPCODE_WIDTH-1:0]         decode_opc_insn_i,

    // Control signal outputs to execute stage

    output reg                            execute_rf_wb_o,

    output reg                            execute_op_alu_o,

    output reg                            execute_op_setflag_o,

    output reg                            execute_op_jbr_o,

    output reg                            execute_op_jr_o,

    output reg                            execute_op_jal_o,

    output reg                            execute_op_brcond_o,

    output reg                            execute_op_branch_o,

    output reg                            execute_op_lsu_load_o,

    output reg                            execute_op_lsu_store_o,

    output reg                            execute_op_lsu_atomic_o,

    output reg [1:0]                       execute_lsu_length_o,

    output reg                            execute_lsu_zext_o,

    output reg                            execute_op_mfspr_o,

    output reg                            execute_op_mtspr_o,

    output reg                            execute_op_rfe_o,

    output reg                            execute_op_add_o,

    output reg                            execute_op_mul_o,

    output reg                            execute_op_mul_signed_o,

    output reg                            execute_op_mul_unsigned_o,

    output reg                            execute_op_div_o,

    output reg                            execute_op_div_signed_o,

    output reg                            execute_op_div_unsigned_o,

    output reg                            execute_op_shift_o,

    output reg                            execute_op_ffl1_o,

    output reg                            execute_op_movhi_o,

    output reg [OPTION_OPERAND_WIDTH-1:0] execute_jal_result_o,

    output reg [`OR1K_OPCODE_WIDTH-1:0]   execute_opc_insn_o,

    // branch detection

    output                                decode_branch_o,

    output [OPTION_OPERAND_WIDTH-1:0]      decode_branch_target_o,

    // exceptions in

    input                                 decode_except_ibus_err_i,

    input                                 decode_except_itlb_miss_i,

    input                                 decode_except_ipagefault_i,

    input                                 decode_except_illegal_i,

    input                                 decode_except_syscall_i,

    input                                 decode_except_trap_i,

    // exception output -

    output reg                            execute_except_ibus_err_o,

    output reg                            execute_except_itlb_miss_o,

    output reg                            execute_except_ipagefault_o,

    output reg                            execute_except_illegal_o,

    output reg                            execute_except_ibus_align_o,

    output reg                            execute_except_syscall_o,

    output reg                            execute_except_trap_o,

    output reg [OPTION_OPERAND_WIDTH-1:0] pc_execute_o,

    // output is valid, signal

    output reg                            decode_valid_o,

    output                                decode_bubble_o,

    output reg                            execute_bubble_o

    );

   wire                            ctrl_to_decode_interlock;

   wire                            branch_to_imm;

   wire [OPTION_OPERAND_WIDTH-1:0] branch_to_imm_target;

   wire                            branch_to_reg;

   wire                            decode_except_ibus_align;

   wire [OPTION_OPERAND_WIDTH-1:0] next_pc_after_branch_insn;

   wire [OPTION_OPERAND_WIDTH-1:0] decode_mispredict_target;

   // Op control signals to execute stage

   always @(posedge clk `OR_ASYNC_RST)

     if (rst) begin

        execute_op_alu_o <= 1'b0;

        execute_op_add_o <= 1'b0;

        execute_op_mul_o <= 1'b0;

        execute_op_mul_signed_o <= 1'b0;

        execute_op_mul_unsigned_o <= 1'b0;

        execute_op_div_o <= 1'b0;

        execute_op_div_signed_o <= 1'b0;

        execute_op_div_unsigned_o <= 1'b0;

        execute_op_shift_o <= 1'b0;

        execute_op_ffl1_o <= 1'b0;

        execute_op_movhi_o <= 1'b0;

        execute_op_mfspr_o <= 1'b0;

        execute_op_mtspr_o <= 1'b0;

        execute_op_lsu_load_o <= 1'b0;

        execute_op_lsu_store_o <= 1'b0;

        execute_op_lsu_atomic_o <= 1'b0;

        execute_op_setflag_o <= 1'b0;

        execute_op_jbr_o <= 1'b0;

        execute_op_jr_o <= 1'b0;

        execute_op_jal_o <= 1'b0;

        execute_op_brcond_o <= 1'b0;

        execute_op_branch_o <= 0;

     end else if (pipeline_flush_i) begin

        execute_op_alu_o <= 1'b0;

        execute_op_add_o <= 1'b0;

        execute_op_mul_o <= 1'b0;

        execute_op_mul_signed_o <= 1'b0;

        execute_op_mul_unsigned_o <= 1'b0;

        execute_op_div_o <= 1'b0;

        execute_op_div_signed_o <= 1'b0;

        execute_op_div_unsigned_o <= 1'b0;

        execute_op_shift_o <= 1'b0;

        execute_op_ffl1_o <= 1'b0;

        execute_op_movhi_o <= 1'b0;

        execute_op_lsu_load_o <= 1'b0;

        execute_op_lsu_store_o <= 1'b0;

        execute_op_lsu_atomic_o <= 1'b0;

        execute_op_setflag_o <= 1'b0;

        execute_op_jbr_o <= 1'b0;

        execute_op_jr_o <= 1'b0;

        execute_op_jal_o <= 1'b0;

        execute_op_brcond_o <= 1'b0;

        execute_op_branch_o <= 1'b0;

     end else if (padv_i) begin

        execute_op_alu_o <= decode_op_alu_i;

        execute_op_add_o <= decode_op_add_i;

        execute_op_mul_o <= decode_op_mul_i;

        execute_op_mul_signed_o <= decode_op_mul_signed_i;

        execute_op_mul_unsigned_o <= decode_op_mul_unsigned_i;

        execute_op_div_o <= decode_op_div_i;

        execute_op_div_signed_o <= decode_op_div_signed_i;

        execute_op_div_unsigned_o <= decode_op_div_unsigned_i;

        execute_op_shift_o <= decode_op_shift_i;

        execute_op_ffl1_o <= decode_op_ffl1_i;

        execute_op_movhi_o <= decode_op_movhi_i;

        execute_op_mfspr_o <= decode_op_mfspr_i;

        execute_op_mtspr_o <= decode_op_mtspr_i;

        execute_op_lsu_load_o <= decode_op_lsu_load_i;

        execute_op_lsu_store_o <= decode_op_lsu_store_i;

        execute_op_lsu_atomic_o <= decode_op_lsu_atomic_i;

        execute_op_setflag_o <= decode_op_setflag_i;

        execute_op_jbr_o <= decode_op_jbr_i;

        execute_op_jr_o <= decode_op_jr_i;

        execute_op_jal_o <= decode_op_jal_i;

        execute_op_brcond_o <= decode_op_brcond_i;

        execute_op_branch_o <= decode_op_branch_i;

        if (decode_bubble_o) begin

           execute_op_alu_o <= 1'b0;

           execute_op_add_o <= 1'b0;

           execute_op_mul_o <= 1'b0;

           execute_op_mul_signed_o <= 1'b0;

           execute_op_mul_unsigned_o <= 1'b0;

           execute_op_div_o <= 1'b0;

           execute_op_div_signed_o <= 1'b0;

           execute_op_div_unsigned_o <= 1'b0;

           execute_op_shift_o <= 1'b0;

           execute_op_ffl1_o <= 1'b0;

           execute_op_movhi_o <= 1'b0;

           execute_op_mtspr_o <= 1'b0;

           execute_op_mfspr_o <= 1'b0;

           execute_op_lsu_load_o <= 1'b0;

           execute_op_lsu_store_o <= 1'b0;

           execute_op_lsu_atomic_o <= 1'b0;

           execute_op_setflag_o <= 1'b0;

           execute_op_jbr_o <= 1'b0;

           execute_op_jr_o <= 1'b0;

           execute_op_jal_o <= 1'b0;

           execute_op_brcond_o <= 1'b0;

           execute_op_branch_o <= 1'b0;

        end

     end

   // rfe is a special case, instead of pushing the pipeline full

   // of nops on a decode_bubble_o, we push it full of rfes.

   // The reason for this is that we need the rfe to reach control

   // stage so it will cause the branch.

   // It will clear itself by the pipeline_flush_i that the rfe

   // will generate.

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_op_rfe_o <= 0;

     else if (pipeline_flush_i)

       execute_op_rfe_o <= 0;

     else if (padv_i)

       execute_op_rfe_o <= decode_op_rfe_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst) begin

        execute_rf_wb_o <= 0;

     end else if (pipeline_flush_i) begin

        execute_rf_wb_o <= 0;

     end else if (padv_i) begin

        execute_rf_wb_o <= decode_rf_wb_i;

        if (decode_bubble_o)

          execute_rf_wb_o <= 0;

     end

   always @(posedge clk)

     if (padv_i)

       execute_rfd_adr_o <= decode_rfd_adr_i;

   always @(posedge clk)

     if (padv_i) begin

        execute_lsu_length_o <= decode_lsu_length_i;

        execute_lsu_zext_o <= decode_lsu_zext_i;

     end

   always @(posedge clk)

     if (padv_i) begin

        execute_imm16_o <= decode_imm16_i;

        execute_immediate_o <= decode_immediate_i;

        execute_immediate_sel_o <= decode_immediate_sel_i;

     end

   always @(posedge clk)

     if (padv_i )

       execute_immjbr_upper_o <= decode_immjbr_upper_i;

   always @(posedge clk)

     if (padv_i) begin

        execute_opc_alu_o <= decode_opc_alu_i;

        execute_opc_alu_secondary_o <= decode_opc_alu_secondary_i;

     end

   always @(posedge clk `OR_ASYNC_RST)

     if (rst) begin

        execute_opc_insn_o <= `OR1K_OPCODE_NOP;

     end else if (pipeline_flush_i) begin

        execute_opc_insn_o <= `OR1K_OPCODE_NOP;

     end else if (padv_i) begin

        execute_opc_insn_o <= decode_opc_insn_i;

        if (decode_bubble_o)

          execute_opc_insn_o <= `OR1K_OPCODE_NOP;

     end

   always @(posedge clk `OR_ASYNC_RST)

     if (rst) begin

        execute_adder_do_sub_o <= 1'b0;

        execute_adder_do_carry_o <= 1'b0;

     end else if (pipeline_flush_i) begin

        execute_adder_do_sub_o <= 1'b0;

        execute_adder_do_carry_o <= 1'b0;

     end else if (padv_i) begin

        execute_adder_do_sub_o <= decode_adder_do_sub_i;

        execute_adder_do_carry_o <= decode_adder_do_carry_i;

        if (decode_bubble_o) begin

           execute_adder_do_sub_o <= 1'b0;

           execute_adder_do_carry_o <= 1'b0;

        end

     end

   // Decode for system call exception

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_syscall_o <= 0;

     else if (padv_i && FEATURE_SYSCALL=="ENABLED")

       execute_except_syscall_o <= decode_except_syscall_i;

   // Decode for system call exception

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_trap_o <= 0;

     else if (padv_i && FEATURE_TRAP=="ENABLED")

       execute_except_trap_o <= decode_except_trap_i;

   // Decode Illegal instruction

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_illegal_o <= 0;

     else if (padv_i)

       execute_except_illegal_o <= decode_except_illegal_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_ibus_err_o <= 1'b0;

     else if (padv_i)

       execute_except_ibus_err_o <= decode_except_ibus_err_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_itlb_miss_o <= 1'b0;

     else if (padv_i)

       execute_except_itlb_miss_o <= decode_except_itlb_miss_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_ipagefault_o <= 1'b0;

     else if (padv_i)

       execute_except_ipagefault_o <= decode_except_ipagefault_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_except_ibus_align_o <= 1'b0;

     else if (padv_i)

       execute_except_ibus_align_o <= decode_except_ibus_align;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       decode_valid_o <= 0;

     else

       decode_valid_o <= padv_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (padv_i)

       pc_execute_o <= pc_decode_i;

   // Branch detection

   assign ctrl_to_decode_interlock = (ctrl_op_lsu_load_i | ctrl_op_mfspr_i |

                                      ctrl_op_mul_i &

                                      FEATURE_MULTIPLIER=="PIPELINED") &

                                     ((decode_rfa_adr_i == ctrl_rfd_adr_i) ||

                                      (decode_rfb_adr_i == ctrl_rfd_adr_i));

   assign branch_to_imm = (decode_op_jbr_i &

                           // l.j/l.jal

                           (!(|decode_opc_insn_i[2:1]) |

                            // l.bf/bnf and flag is right

                            (decode_opc_insn_i[2] == predicted_flag_i)));

   assign branch_to_imm_target = pc_decode_i + {{4{decode_immjbr_upper_i[9]}},

                                                decode_immjbr_upper_i,

                                                decode_imm16_i,2'b00};

   assign branch_to_reg = decode_op_jr_i &

                          !(ctrl_to_decode_interlock |

                            execute_rf_wb_o &

                            (decode_rfb_adr_i == execute_rfd_adr_o));

   assign decode_branch_o = (branch_to_imm | branch_to_reg) &

                            !pipeline_flush_i;

   assign decode_branch_target_o = branch_to_imm ?

                                   branch_to_imm_target :

                                   // If a bubble have been pushed out to get

                                   // the instruction that will write the

                                   // branch target to control stage, then we

                                   // need to use the register result from

                                   // execute stage instead of decode stage.

                                   execute_bubble_o | execute_op_jr_o ?

                                   execute_rfb_i : decode_rfb_i;

   assign decode_except_ibus_align = decode_branch_o &

                                     (|decode_branch_target_o[1:0]);

   assign next_pc_after_branch_insn = FEATURE_DELAY_SLOT == "ENABLED" ?

                                      pc_decode_i + 8 : pc_decode_i + 4;

   assign decode_mispredict_target = decode_op_bf_i & !predicted_flag_i |

                                     decode_op_bnf_i & predicted_flag_i ?

                                     branch_to_imm_target :

                                     next_pc_after_branch_insn;

   // Forward branch prediction signals to execute stage

   always @(posedge clk)

     if (padv_i & decode_op_brcond_i)

       execute_mispredict_target_o <= decode_mispredict_target;

   always @(posedge clk)

     if (padv_i & decode_op_brcond_i)

       execute_predicted_flag_o <= predicted_flag_i;

   // Calculate the link register result

   // TODO: investigate if the ALU adder can be used for this without

   // introducing critical paths

   always @(posedge clk)

     if (padv_i)

       execute_jal_result_o <= next_pc_after_branch_insn;

   // Detect the situation where there is an instruction in execute stage

   // that will produce it's result in control stage (i.e. load and mfspr),

   // and an instruction currently in decode stage needing it's result as

   // input in execute stage.

   // Also detect the situation where there is a jump to register in decode

   // stage and an instruction in execute stage that will write to that

   // register.

   //

   // A bubble is also inserted when an rfe instruction is in decode stage,

   // the main purpose of this is to stall fetch while the rfe is propagating

   // up to ctrl stage.

   assign decode_bubble_o = (

                             // load/mfspr/mul

                             (execute_op_lsu_load_o | execute_op_mfspr_o |

                              execute_op_mul_o &

                              FEATURE_MULTIPLIER=="PIPELINED") &

                             (decode_rfa_adr_i == execute_rfd_adr_o ||

                              decode_rfb_adr_i == execute_rfd_adr_o) |

                             // mul

                             FEATURE_MULTIPLIER=="PIPELINED" &

                             (decode_op_mul_i &

                              (ctrl_to_decode_interlock |

                               execute_rf_wb_o &

                               (decode_rfa_adr_i == execute_rfd_adr_o ||

                                decode_rfb_adr_i == execute_rfd_adr_o))) |

                             // jr

                             decode_op_jr_i &

                             (ctrl_to_decode_interlock |

                              execute_rf_wb_o &

                              (decode_rfb_adr_i == execute_rfd_adr_o)) |

                             // atomic store

                             execute_op_lsu_store_o & execute_op_lsu_atomic_o |

                             // rfe

                             decode_op_rfe_i

                             ) & padv_i;

   always @(posedge clk `OR_ASYNC_RST)

     if (rst)

       execute_bubble_o <= 0;

     else if (pipeline_flush_i)

       execute_bubble_o <= 0;

     else if (padv_i)

       execute_bubble_o <= decode_bubble_o;

endmodule // mor1kx_decode_execute_cappuccino