以下是用 Verilog 实现 AXI MASTER 的代码示例，每次传输大小为 32 字节，数据位宽为 64 位。

module axi_master(
    input wire clk,
    input wire rst_n,
    // AXI 接口信号
    output reg [31:0] awaddr,
    output reg [7:0] awlen,
    output reg [2:0] awsize,
    output reg [1:0] awburst,
    output reg awvalid,
    input wire awready,
    output reg [63:0] wdata,
    output reg [7:0] wstrb,
    output reg wlast,
    output reg wvalid,
    input wire wready,
    input wire [1:0] bresp,
    input wire bvalid,
    output reg bready,
    output reg [31:0] araddr,
    output reg [7:0] arlen,
    output reg [2:0] arsize,
    output reg [1:0] arburst,
    output reg arvalid,
    input wire arready,
    input wire [63:0] rdata,
    input wire [1:0] rresp,
    input wire rlast,
    input wire rvalid,
    output reg rready
);

// 状态定义
localparam IDLE = 3'b000;
localparam WRITE_ADDR = 3'b001;
localparam WRITE_DATA = 3'b010;
localparam WRITE_RESP = 3'b011;
localparam READ_ADDR = 3'b100;
localparam READ_DATA = 3'b101;

reg [2:0] current_state, next_state;

// 第一段：状态转移
always @(posedge clk or negedge rst_n) begin
    if (!rst_n) begin
        current_state <= IDLE;
    end else begin
        current_state <= next_state;
    end
end

// 第二段：状态转移条件
always @(*) begin
    case (current_state)
        IDLE: begin
            next_state = WRITE_ADDR;
        end
        WRITE_ADDR: begin
            if (awready) begin
                next_state = WRITE_DATA;
            end else begin
                next_state = WRITE_ADDR;
            end
        end
        WRITE_DATA: begin
            if (wlast && wready) begin
                next_state = WRITE_RESP;
            end else begin
                next_state = WRITE_DATA;
            end
        end
        WRITE_RESP: begin
            if (bvalid) begin
                next_state = READ_ADDR;
            end else begin
                next_state = WRITE_RESP;
            end
        end
        READ_ADDR: begin
            if (arready) begin
                next_state = READ_DATA;
            end else begin
                next_state = READ_ADDR;
            end
        end
        READ_DATA: begin
            if (rlast && rvalid) begin
                next_state = IDLE;
            end else begin
                next_state = READ_DATA;
            end
        end
        default: next_state = IDLE;
    endcase
end

// 第三段：输出逻辑
always @(posedge clk or negedge rst_n) begin
    if (!rst_n) begin
        awaddr <= 32'h0;
        awlen <= 8'h0;
        awsize <= 3'h2; // 32 字节传输对应 size 为 2（64 位数据位宽）
        awburst <= 2'b01;
        awvalid <= 1'b0;
        wdata <= 64'h0;
        wstrb <= 8'hFF;
        wlast <= 1'b0;
        wvalid <= 1'b0;
        bready <= 1'b0;
        araddr <= 32'h0;
        arlen <= 8'h0;
        arsize <= 3'h2;
        arburst <= 2'b01;
        arvalid <= 1'b0;
        rready <= 1'b0;
    end else begin
        case (current_state)
            IDLE: begin
                awaddr <= 32'h1000; // 设置起始地址
                awlen <= 8'd3; // 总共传输 4 个突发（32 字节）
                awvalid <= 1'b1;
            end
            WRITE_ADDR: begin
                awvalid <= 1'b0;
            end
            WRITE_DATA: begin
                if (wready) begin
                    wdata <= wdata + 64'h1;
                    if (wdata == {64{1'b1}}) begin
                        wlast <= 1'b1;
                    end
                    wvalid <= 1'b1;
                end else begin
                    wvalid <= 1'b0;
                end
            end
            WRITE_RESP: begin
                bready <= 1'b1;
            end
            READ_ADDR: begin
                araddr <= 32'h1000;
                arlen <= 8'd3;
                arvalid <= 1'b1;
            end
            READ_DATA: begin
                if (rvalid) begin
                    rready <= 1'b0;
                    if (rlast) begin
                        rready <= 1'b0;
                    end else begin
                        rready <= 1'b1;
                    end
                end
            end
            default: begin
                // 默认状态下的输出赋值
                awaddr <= 32'h0;
                awvalid <= 1'b0;
                wdata <= 64'h0;
                wvalid <= 1'b0;
                bready <= 1'b0;
                araddr <= 32'h0;
                arvalid <= 1'b0;
                rready <= 1'b0;
            end
        endcase
    end
end

endmodule

在这个实现中，状态机分为三段。第一段负责状态的转移，在时钟上升沿或复位信号下降沿时更新当前状态。第二段根据当前状态确定下一个状态，考虑了各种 AXI 信号的就绪情况。第三段根据当前状态对 AXI Master 的输出信号进行赋值，控制写地址、写数据、等待写响应、读地址和读数据的过程。每次传输的数据大小为 32 字节，数据位宽为 64 位。