Verilogを用いたMIPSプロセッサの基本構造と活用17選

module and_gate(
    input a,
    input b,
    output y
);

assign y = a & b;

endmodule

module register_file(
    input clk,
    input reset,
    input [4:0] read_reg1,
    input [4:0] read_reg2,
    input [4:0] write_reg,
    input [31:0] write_data,
    input reg_write,
    output [31:0] read_data1,
    output [31:0] read_data2
);

reg [31:0] registers [0:31];
integer i;

always @(posedge clk or posedge reset) begin
    if (reset) begin
        for (i = 0; i < 32; i = i + 1) begin
            registers[i] <= 32'b0;
        end
    end else if (reg_write) begin
        registers[write_reg] <= write_data;
    end
end

assign read_data1 = registers[read_reg1];
assign read_data2 = registers[read_reg2];

endmodule

module alu(
    input [31:0] a,
    input [31:0] b,
    input [3:0] alu_control,
    output reg [31:0] result,
    output zero
);

always @(*) begin
    case (alu_control)
        4'b0000: result = a & b; // AND
        4'b0001: result = a | b; // OR
        4'b0010: result = a + b; // ADD
        4'b0110: result = a - b; // SUB
        4'b0111: result = (a < b) ? 32'd1 : 32'd0; // SLT
        default: result = 32'b0;
    endcase
end

assign zero = (result == 32'b0);

endmodule

module control_unit(
    input [5:0] opcode,
    output reg reg_dst,
    output reg branch,
    output reg mem_read,
    output reg mem_to_reg,
    output reg [1:0] alu_op,
    output reg mem_write,
    output reg alu_src,
    output reg reg_write
);

always @(*) begin
    case(opcode)
        6'b000000: begin // R-type
            reg_dst = 1'b1;
            alu_src = 1'b0;
            mem_to_reg = 1'b0;
            reg_write = 1'b1;
            mem_read = 1'b0;
            mem_write = 1'b0;
            branch = 1'b0;
            alu_op = 2'b10;
        end
        6'b100011: begin // lw
            reg_dst = 1'b0;
            alu_src = 1'b1;
            mem_to_reg = 1'b1;
            reg_write = 1'b1;
            mem_read = 1'b1;
            mem_write = 1'b0;
            branch = 1'b0;
            alu_op = 2'b00;
        end
        // その他の命令タイプも同様に実装
        default: begin
            // デフォルト値を設定
        end
    endcase
end

endmodule

module memory_interface(
    input clk,
    input [31:0] address,
    input [31:0] write_data,
    input mem_read,
    input mem_write,
    output reg [31:0] read_data
);

reg [31:0] memory [0:1023]; // 1024ワードのメモリ

always @(posedge clk) begin
    if (mem_write)
        memory[address[11:2]] <= write_data;
end

always @(*) begin
    if (mem_read)
        read_data = memory[address[11:2]];
    else
        read_data = 32'b0;
end

endmodule

module arithmetic_unit(
    input [31:0] operand_a,
    input [31:0] operand_b,
    input [2:0] function_code,
    output reg [31:0] result
);

always @(*) begin
    case(function_code)
        3'b000: result = operand_a + operand_b; // ADD
        3'b001: result = operand_a - operand_b; // SUB
        default: result = 32'b0;
    endcase
end

endmodule

module logical_unit(
    input [31:0] operand_a,
    input [31:0] operand_b,
    input [2:0] function_code,
    output reg [31:0] result
);

always @(*) begin
    case(function_code)
        3'b000: result = operand_a & operand_b; // AND
        3'b001: result = operand_a | operand_b; // OR
        3'b010: result = operand_a ^ operand_b; // XOR
        default: result = 32'b0;
    endcase
end

endmodule

module branch_unit(
    input [31:0] operand_a,
    input [31:0] operand_b,
    input [1:0] branch_type,
    output reg branch_taken
);

always @(*) begin
    case(branch_type)
        2'b00: branch_taken = (operand_a == operand_b); // BEQ
        2'b01: branch_taken = (operand_a != operand_b); // BNE
        default: branch_taken = 1'b0;
    endcase
end

endmodule

module memory_access_unit(
    input clk,
    input [31:0] address,
    input [31:0] write_data,
    input mem_read,
    input mem_write,
    output reg [31:0] read_data
);

reg [31:0] memory [0:1023]; // 1024ワードのメモリ

always @(posedge clk) begin
    if (mem_write)
        memory[address[11:2]] <= write_data;
end

always @(*) begin
    if (mem_read)
        read_data = memory[address[11:2]];
    else
        read_data = 32'b0;
end

endmodule

module mips_pipeline(
    input clk,
    input reset
);

// パイプラインステージ間のレジスタ
reg [31:0] IF_ID_IR, IF_ID_PC;
reg [31:0] ID_EX_IR, ID_EX_A, ID_EX_B, ID_EX_IMM;
reg [31:0] EX_MEM_IR, EX_MEM_ALUOut, EX_MEM_B;
reg [31:0] MEM_WB_IR, MEM_WB_ALUOut, MEM_WB_LMD;

// 各ステージの処理
always @(posedge clk or posedge reset) begin
    if (reset) begin
        // リセット処理
    end else begin
        // IF stage
        // ID stage
        // EX stage
        // MEM stage
        // WB stage
    end
end

endmodule

module pipeline_register(
    input clk,
    input reset,
    input [31:0] in_data,
    output reg [31:0] out_data
);

always @(posedge clk or posedge reset) begin
    if (reset)
        out_data <= 32'b0;
    else
        out_data <= in_data;
end

endmodule

module hazard_detection_unit(
    input [4:0] rs, rt,
    input [4:0] ex_rd, mem_rd,
    input ex_reg_write, mem_reg_write,
    output reg [1:0] forward_a, forward_b
);

always @(*) begin
    // EXステージでのフォワーディング
    if (ex_reg_write && (ex_rd != 0) && (ex_rd == rs))
        forward_a = 2'b10;
    // MEMステージでのフォワーディング
    else if (mem_reg_write && (mem_rd != 0) && (mem_rd == rs))
        forward_a = 2'b01;
    else
        forward_a = 2'b00;

    // rtに対しても同様の処理
    if (ex_reg_write && (ex_rd != 0) && (ex_rd == rt))
        forward_b = 2'b10;
    else if (mem_reg_write && (mem_rd != 0) && (mem_rd == rt))
        forward_b = 2'b01;
    else
        forward_b = 2'b00;
end

endmodule

module branch_predictor(
    input [31:0] pc,
    input [31:0] instruction,
    output reg predict_taken
);

wire [5:0] opcode = instruction[31:26];
wire [15:0] immediate = instruction[15:0];

always @(*) begin
    // 常に分岐しないと予測（静的予測）
    predict_taken = 1'b0;

    // 後方分岐の場合は分岐すると予測
    if (opcode == 6'b000100 && immediate[15] == 1'b1)
        predict_taken = 1'b1;
end

endmodule

// タイミング違反を起こしやすい設計
module long_path(
    input clk,
    input [31:0] a, b, c, d,
    output reg [31:0] result
);

always @(posedge clk) begin
    result <= ((a + b) * c) / d;
end

endmodule

// パイプライン化による改善
module pipelined_path(
    input clk,
    input [31:0] a, b, c, d,
    output reg [31:0] result
);

reg [31:0] stage1, stage2;

always @(posedge clk) begin
    stage1 <= a + b;
    stage2 <= stage1 * c;
    result <= stage2 / d;
end

endmodule

// エラーを含むコード
module syntax_error(
    input a,
    input b,
    output y
);

assign y = a & b  // セミコロンが欠落している

endmodule

// 修正後のコード
module syntax_error_fixed(
    input a,
    input b,
    output y
);

assign y = a & b;  // セミコロンを追加

endmodule

module debug_example(
    input clk,
    input reset,
    input [7:0] data_in,
    output reg [7:0] data_out
);

reg [7:0] internal_state;

// デバッグ用の信号
wire debug_condition = (data_in == 8'hFF);

always @(posedge clk or posedge reset) begin
    if (reset) begin
        internal_state <= 8'h00;
        data_out <= 8'h00;
    end else begin
        if (debug_condition) begin
            internal_state <= data_in;
        end else begin
            internal_state <= internal_state + 1;
        end
        data_out <= internal_state;
    end
end

endmodule

always @(posedge clk) begin
    $display("Time %t: data_in = %h, internal_state = %h, data_out = %h", 
             $time, data_in, internal_state, data_out);
end

module simple_calculator(
    input clk,
    input reset,
    input [3:0] operation,  // 0: 加算, 1: 減算, 2: 乗算, 3: 除算
    input [31:0] operand_a,
    input [31:0] operand_b,
    output reg [31:0] result,
    output reg error  // 0除算エラーフラグ
);

always @(posedge clk or posedge reset) begin
    if (reset) begin
        result <= 32'h00000000;
        error <= 1'b0;
    end else begin
        case (operation)
            4'b0000: result <= operand_a + operand_b;
            4'b0001: result <= operand_a - operand_b;
            4'b0010: result <= operand_a * operand_b;
            4'b0011: begin
                if (operand_b == 32'h00000000) begin
                    error <= 1'b1;
                    result <= 32'hFFFFFFFF;  // エラー値
                end else begin
                    error <= 1'b0;
                    result <= operand_a / operand_b;
                end
            end
            default: result <= 32'h00000000;
        endcase
    end
end

endmodule

module image_coprocessor(
    input clk,
    input reset,
    input [7:0] pixel_in,
    input process_enable,
    output reg [7:0] pixel_out
);

always @(posedge clk or posedge reset) begin
    if (reset) begin
        pixel_out <= 8'h00;
    end else if (process_enable) begin
        pixel_out <= 8'hFF - pixel_in;  // 輝度反転
    end
end

endmodule

module uart_interface(
    input clk,
    input reset,
    input rx,
    output tx,
    input [7:0] tx_data,
    input tx_start,
    output reg [7:0] rx_data,
    output reg rx_done,
    output reg tx_busy
);

// UART parameters
parameter CLKS_PER_BIT = 100;  // クロック周波数 / ボーレート

// State machine states
parameter IDLE = 2'b00;
parameter START_BIT = 2'b01;
parameter DATA_BITS = 2'b10;
parameter STOP_BIT = 2'b11;

reg [1:0] rx_state = IDLE;
reg [1:0] tx_state = IDLE;
reg [7:0] rx_shift_reg;
reg [7:0] tx_shift_reg;
reg [7:0] bit_counter;
reg [7:0] clk_counter;

// Receiver logic
always @(posedge clk or posedge reset) begin
    if (reset) begin
        rx_state <= IDLE;
        rx_data <= 8'h00;
        rx_done <= 1'b0;
    end else begin
        case (rx_state)
            IDLE: begin
                if (rx == 1'b0) begin  // Start bit detected
                    rx_state <= START_BIT;
                    bit_counter <= 8'h00;
                    clk_counter <= 8'h00;
                end
            end
            START_BIT: begin
                if (clk_counter == CLKS_PER_BIT - 1) begin
                    rx_state <= DATA_BITS;
                    clk_counter <= 8'h00;
                end else begin
                    clk_counter <= clk_counter + 1;
                end
            end
            DATA_BITS: begin
                if (clk_counter == CLKS_PER_BIT - 1) begin
                    clk_counter <= 8'h00;
                    rx_shift_reg <= {rx, rx_shift_reg[7:1]};
                    if (bit_counter == 7) begin
                        rx_state <= STOP_BIT;
                    end else begin
                        bit_counter <= bit_counter + 1;
                    end
                end else begin
                    clk_counter <= clk_counter + 1;
                end
            end
            STOP_BIT: begin
                if (clk_counter == CLKS_PER_BIT - 1) begin
                    rx_state <= IDLE;
                    rx_data <= rx_shift_reg;
                    rx_done <= 1'b1;
                end else begin
                    clk_counter <= clk_counter + 1;
                end
            end
        endcase
    end
end

// Transmitter logic
always @(posedge clk or posedge reset) begin
    if (reset) begin
        tx_state <= IDLE;
        tx_busy <= 1'b0;
    end else begin
        case (tx_state)
            IDLE: begin
                if (tx_start) begin
                    tx_state <= START_BIT;
                    tx_shift_reg <= tx_data;
                    tx_busy <= 1'b1;
                    bit_counter <= 8'h00;
                    clk_counter <= 8'h00;
                end
            end
            START_BIT: begin
                if (clk_counter == CLKS_PER_BIT - 1) begin
                    tx_state <= DATA_BITS;
                    clk_counter <= 8'h00;
                end else begin
                    clk_counter <= clk_counter + 1;
                end
            end
            DATA_BITS: begin
                if (clk_counter == CLKS_PER_BIT - 1) begin
                    clk_counter <= 8'h00;
                    tx_shift_reg <= {1'b0, tx_shift_reg[7:1]};
                    if (bit_counter == 7) begin
                        tx_state <= STOP_BIT;
                    end else begin
                        bit_counter <= bit_counter + 1;
                    end
                end else begin
                    clk_counter <= clk_counter + 1;
                end
            end
            STOP_BIT: begin
                if (clk_counter == CLKS_PER_BIT - 1) begin
                    tx_state <= IDLE;
                    tx_busy <= 1'b0;
                end else begin
                    clk_counter <= clk_counter + 1;
                end
            end
        endcase
    end
end

assign tx = (tx_state == IDLE) ? 1'b1 :
            (tx_state == START_BIT) ? 1'b0 :
            (tx_state == DATA_BITS) ? tx_shift_reg[0] :
            1'b1;  // STOP_BIT

endmodule

module direct_mapped_cache(
    input clk,
    input reset,
    input [31:0] address,
    input [31:0] write_data,
    input write_enable,
    input read_enable,
    output reg [31:0] read_data,
    output reg hit
);

parameter CACHE_SIZE = 256;  // キャッシュラインの数
parameter LINE_SIZE = 32;    // キャッシュラインのビット幅
parameter TAG_SIZE = 20;     // タグのビット幅

reg [LINE_SIZE-1:0] cache_data [0:CACHE_SIZE-1];
reg [TAG_SIZE-1:0] cache_tags [0:CACHE_SIZE-1];
reg [CACHE_SIZE-1:0] valid;

wire [TAG_SIZE-1:0] tag = address[31:12];
wire [7:0] index = address[11:4];
wire [3:0] offset = address[3:0];

always @(posedge clk or posedge reset) begin
    if (reset) begin
        integer i;
        for (i = 0; i < CACHE_SIZE; i = i + 1) begin
            valid[i] <= 1'b0;
            cache_tags[i] <= {TAG_SIZE{1'b0}};
            cache_data[i] <= {LINE_SIZE{1'b0}};
        end
        read_data <= 32'h00000000;
        hit <= 1'b0;
    end else begin
        if (read_enable) begin
            if (valid[index] && cache_tags[index] == tag) begin
                read_data <= cache_data[index];
                hit <= 1'b1;
            end else begin
                hit <= 1'b0;
                // ここでメインメモリからデータを読み込む処理を追加
            end
        end else if (write_enable) begin
            cache_data[index] <= write_data;
            cache_tags[index] <= tag;
            valid[index] <= 1'b1;
            hit <= 1'b1;
        end else begin
            hit <= 1'b0;
        end
    end
end

endmodule