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[/] [rtl/] [machine_control.v] - Rev 11

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//////////////////////////////////////////////////////////////////////////////////
// Engineer: Rafael de Oliveira Calçada (rafaelcalcada@gmail.com) 
// 
// Create Date: 26.04.2020 23:18:08
// Module Name: machine_control
// Project Name: Steel Core 
// Description: Controls the core operation in M-mode 
// 
// Dependencies: globals.vh
// 
// Version 0.01
// 
//////////////////////////////////////////////////////////////////////////////////
 
/*********************************************************************************
 
MIT License
 
Copyright (c) 2020 Rafael de Oliveira Calçada
 
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
 
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
 
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
 
********************************************************************************/
 
`timescale 1ns / 1ps
`include "globals.vh"
 
module machine_control(
 
    input wire CLK,
    input wire RESET,
 
    // from control unit
    input wire ILLEGAL_INSTR,
    input wire MISALIGNED_LOAD,
    input wire MISALIGNED_STORE,
 
    // from pipeline stage 1
    input wire MISALIGNED_INSTR,
 
    // from instruction
    input wire [6:2] OPCODE_6_TO_2,
    input wire [2:0] FUNCT3,
    input wire [6:0] FUNCT7,
    input wire [4:0] RS1_ADDR,
    input wire [4:0] RS2_ADDR,
    input wire [4:0] RD_ADDR,
 
    // from interrupt controller
    input wire E_IRQ,
    input wire T_IRQ,
    input wire S_IRQ,
 
    // from CSR file
    input wire MIE,
    input wire MEIE,
    input wire MTIE,
    input wire MSIE,
    input wire MEIP,
    input wire MTIP,
    input wire MSIP,         
 
    // to CSR file
    output reg I_OR_E,
    output reg SET_EPC,
    output reg SET_CAUSE,
    output reg [3:0] CAUSE,
    output reg INSTRET_INC,
    output reg MIE_CLEAR,
    output reg MIE_SET,
    output reg MISALIGNED_EXCEPTION,
 
    // to PC MUX
    output reg [1:0] PC_SRC,
 
    // to pipeline stage 2 register
    output reg FLUSH,
 
    // to Control Unit
    output wire TRAP_TAKEN
 
    );
 
    // state registers
    reg [3:0] curr_state;
    reg [3:0] next_state;
 
    // machine states
    parameter STATE_RESET         = 4'b0001; 
    parameter STATE_OPERATING     = 4'b0010;
    parameter STATE_TRAP_TAKEN    = 4'b0100;    
    parameter STATE_TRAP_RETURN   = 4'b1000;
 
    // internal control signals
    wire exception;
    wire ip;
    wire eip;
    wire tip;
    wire sip;
    wire is_system;
    wire RS1_ADDR_zero;
    wire RS2_ADDR_zero;
    wire rd_zero;
    wire RS2_ADDR_mret;
    wire RS2_ADDR_ebreak;
    wire FUNCT3_zero;
    wire FUNCT7_zero;
    wire FUNCT7_mret;
    wire csr;
    wire mret;
    wire ecall;
    wire ebreak;
    reg pre_instret_inc;
 
    // COMBINATIONAL LOGIC -------------------------------------------
 
    assign is_system = OPCODE_6_TO_2[6] & OPCODE_6_TO_2[5] & OPCODE_6_TO_2[4] & ~OPCODE_6_TO_2[3] & ~OPCODE_6_TO_2[2];
    assign FUNCT3_zero = ~(FUNCT3[2] | FUNCT3[1] | FUNCT3[0]);
    assign FUNCT7_zero = ~(FUNCT7[6] | FUNCT7[5] | FUNCT7[4] | FUNCT7[3] | FUNCT7[2] | FUNCT7[1] | FUNCT7[0]);
    assign FUNCT7_wfi = ~FUNCT7[6] & ~FUNCT7[5] & ~FUNCT7[4] & FUNCT7[3] & ~FUNCT7[2] & ~FUNCT7[1] & ~FUNCT7[0];
    assign FUNCT7_mret = ~FUNCT7[6] & ~FUNCT7[5] & FUNCT7[4] & FUNCT7[3] & ~FUNCT7[2] & ~FUNCT7[1] & ~FUNCT7[0];
    assign RS1_ADDR_zero = ~(RS1_ADDR[4] | RS1_ADDR[3] | RS1_ADDR[2] | RS1_ADDR[1] | RS1_ADDR[0]);
    assign RS2_ADDR_zero = ~(RS2_ADDR[4] | RS2_ADDR[3] | RS2_ADDR[2] | RS2_ADDR[1] | RS2_ADDR[0]);
    assign rd_zero = ~(RD_ADDR[4] | RD_ADDR[3] | RD_ADDR[2] | RD_ADDR[1] | RD_ADDR[0]);
    assign RS2_ADDR_wfi = ~RS2_ADDR[4] & ~RS2_ADDR[3] & RS2_ADDR[2] & ~RS2_ADDR[1] & RS2_ADDR[0];
    assign RS2_ADDR_mret = ~RS2_ADDR[4] & ~RS2_ADDR[3] & ~RS2_ADDR[2] & RS2_ADDR[1] & ~RS2_ADDR[0];
    assign RS2_ADDR_ebreak = ~RS2_ADDR[4] & ~RS2_ADDR[3] & ~RS2_ADDR[2] & ~RS2_ADDR[1] & RS2_ADDR[0];
    assign mret = is_system & FUNCT7_mret & RS2_ADDR_mret & RS1_ADDR_zero & FUNCT3_zero & rd_zero;
    assign ecall = is_system & FUNCT7_zero & RS2_ADDR_zero & RS1_ADDR_zero & FUNCT3_zero & rd_zero;
    assign ebreak = is_system & FUNCT7_zero & RS2_ADDR_ebreak & RS1_ADDR_zero & FUNCT3_zero & rd_zero;
 
    assign eip = MEIE & (E_IRQ | MEIP);
    assign tip = MTIE & (T_IRQ | MTIP);
    assign sip = MSIE & (S_IRQ | MSIP);
    assign ip = eip | tip | sip;
    assign exception = ILLEGAL_INSTR | MISALIGNED_INSTR | MISALIGNED_LOAD | MISALIGNED_STORE;
    assign TRAP_TAKEN = (MIE & ip) | exception | ecall | ebreak;
 
    always @*
    begin
        case(curr_state)
            STATE_RESET:
                next_state = STATE_OPERATING;
            STATE_OPERATING: 
                if(TRAP_TAKEN) next_state = STATE_TRAP_TAKEN;
                else if(mret) next_state = STATE_TRAP_RETURN;
                else next_state = STATE_OPERATING;
            STATE_TRAP_TAKEN:
                next_state = STATE_OPERATING;
            STATE_TRAP_RETURN:
                next_state = STATE_OPERATING;
            default:
                next_state = STATE_OPERATING;
        endcase
    end
 
    // output generation
    always @*
    begin
        case(curr_state)
            STATE_RESET:
                begin
                    PC_SRC = `PC_BOOT;
                    FLUSH = 1'b1;
                    INSTRET_INC = 1'b0;
                    SET_EPC = 1'b0;
                    SET_CAUSE = 1'b0;
                    MIE_CLEAR = 1'b0;
                    MIE_SET = 1'b0;
                end
            STATE_OPERATING:
                begin
                    PC_SRC = `PC_NEXT;
                    FLUSH = 1'b0;
                    INSTRET_INC = 1'b1;
                    SET_EPC = 1'b0;
                    SET_CAUSE = 1'b0;
                    MIE_CLEAR = 1'b0;
                    MIE_SET = 1'b0;
                end
            STATE_TRAP_TAKEN:
                begin
                    PC_SRC = `PC_TRAP;
                    FLUSH = 1'b1;
                    INSTRET_INC = 1'b0;
                    SET_EPC = 1'b1;
                    SET_CAUSE = 1'b1;
                    MIE_CLEAR = 1'b1;
                    MIE_SET = 1'b0;
                end
            STATE_TRAP_RETURN:
                begin
                    PC_SRC = `PC_EPC;
                    FLUSH = 1'b1;
                    INSTRET_INC = 1'b0;
                    SET_EPC = 1'b0;
                    SET_CAUSE = 1'b0;
                    MIE_CLEAR = 1'b0;
                    MIE_SET = 1'b1;
                end
            default:
                begin
                    PC_SRC = `PC_NEXT;
                    FLUSH = 1'b0;
                    INSTRET_INC = 1'b1;
                    SET_EPC = 1'b0;
                    SET_CAUSE = 1'b0;
                    MIE_CLEAR = 1'b0;
                    MIE_SET = 1'b0;
                end
        endcase
 
    end
 
    // SEQUENTIAL LOGIC -------------------------------------------
 
    always @(posedge CLK)
    begin
        if(RESET) curr_state <= STATE_RESET;
        else curr_state <= next_state;
    end    
 
    always @(posedge CLK)
    begin
        if(RESET) MISALIGNED_EXCEPTION <= 1'b0;
        else MISALIGNED_EXCEPTION <= MISALIGNED_INSTR | MISALIGNED_LOAD | MISALIGNED_STORE;
    end
 
    always @(posedge CLK)
    begin
        if(RESET)
        begin
            CAUSE <= 4'b0;
            I_OR_E <= 1'b0;
        end
        else if(curr_state == STATE_OPERATING)
        begin 
            if(MIE & eip)
            begin
                CAUSE <= 4'b1011; // M-mode external interrupt
                I_OR_E <= 1'b1;
            end            
            else if(MIE & sip)
            begin
                CAUSE <= 4'b0011; // M-mode software interrupt
                I_OR_E <= 1'b1;
            end
            else if(MIE & tip)
            begin
                CAUSE <= 4'b0111; // M-mode timer interrupt
                I_OR_E <= 1'b1;
            end
            else if(ILLEGAL_INSTR)
            begin
                CAUSE <= 4'b0010; // Illegal instruction
                I_OR_E <= 1'b0;
            end
            else if(MISALIGNED_INSTR)
            begin
                CAUSE <= 4'b0000; // Instruction address misaligned
                I_OR_E <= 1'b0;
            end
            else if(ecall)
            begin
                CAUSE <= 4'b1011; // Environment call from M-mode
                I_OR_E <= 1'b0;
            end
            else if(ebreak)
            begin
                CAUSE <= 4'b0011; // Breakpoint
                I_OR_E <= 1'b0;
            end
            else if(MISALIGNED_STORE)
            begin
                CAUSE <= 4'b0110; // Store address misaligned
                I_OR_E <= 1'b0;
            end
            else if(MISALIGNED_LOAD)
            begin
                CAUSE <= 4'b0100; // Load address misaligned
                I_OR_E <= 1'b0;
            end
        end        
    end
 
endmodule
 

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