💾 第25课：SD卡读写

// SD卡SPI模式控制器(简化版)
// 支持CMD0(复位) + CMD8(检查) + CMD17(读扇区)
module sd_spi_ctrl (
    input  wire        clk,
    input  wire        rst,
    // 命令接口
    input  wire [5:0]  cmd,
    input  wire [31:0] cmd_arg,
    input  wire        cmd_start,
    output reg         cmd_busy,
    output reg  [7:0]  rsp_data,
    output reg         rsp_valid,
    // SPI接口(复用SPI Master)
    output reg         spi_clk,
    output reg         spi_mosi,
    input  wire        spi_miso,
    output wire        spi_cs_n
);
    assign spi_cs_n = 0; // SD卡SPI模式CS始终低

    // SPI时钟分频: 400kHz初始化, 25MHz正常
    localparam INIT_DIV = 62;  // 50M/400k/2
    localparam NORM_DIV = 1;   // 50M/25M/2
    reg [7:0] clk_div;
    reg       clk_en;

    always @(posedge clk) begin
        if (rst) clk_div <= 0;
        else begin
            clk_en <= 0;
            if (clk_div >= INIT_DIV) begin
                clk_div <= 0; clk_en <= 1;
            end else clk_div <= clk_div + 1;
        end
    end

    // CMD帧: [01 CMD(6) ARG(32) CRC(7) 1]
    reg [47:0] cmd_frame;
    reg [5:0]  bit_cnt;
    reg [7:0]  crc7;

    // CRC7计算(简化: 预计算常用CMD的CRC)
    always @(*) begin
        case(cmd)
            6'd0:  crc7 = 8'h95; // CMD0 CRC
            6'd8:  crc7 = 8'h87; // CMD8 CRC
            6'd17: crc7 = 8'h00; // CMD17 CRC(简化)
            default: crc7 = 8'hFF;
        endcase
    end

    localparam IDLE=0, SEND_CMD=1, WAIT_RSP=2, READ_DATA=3, DONE=4;
    reg [2:0] state;

    always @(posedge clk) begin
        if (rst) begin
            state <= IDLE; cmd_busy <= 0;
            spi_clk <= 0; spi_mosi <= 1;
            bit_cnt <= 0;
        end else if (clk_en) begin
            rsp_valid <= 0;
            case(state)
                IDLE: begin
                    spi_mosi <= 1;
                    if (cmd_start) begin
                        cmd_frame <= {2'b01, cmd, cmd_arg, crc7[6:0], 1'b1};
                        bit_cnt <= 0;
                        state <= SEND_CMD;
                        cmd_busy <= 1;
                    end
                end
                SEND_CMD: begin
                    spi_clk <= ~spi_clk;
                    if (!spi_clk) begin
                        spi_mosi <= cmd_frame[47];
                        cmd_frame <= {cmd_frame[46:0], 1'bFF};
                    end
                    if (bit_cnt >= 47) state <= WAIT_RSP;
                    else bit_cnt <= bit_cnt + 1;
                end
                WAIT_RSP: begin
                    spi_clk <= ~spi_clk;
                    if (spi_clk && spi_miso == 0) begin
                        rsp_data <= 0;
                        state <= READ_DATA;
                        bit_cnt <= 0;
                    end
                end
                READ_DATA: begin
                    spi_clk <= ~spi_clk;
                    if (spi_clk) begin
                        rsp_data <= {rsp_data[6:0], spi_miso};
                        if (bit_cnt[2:0] == 7) begin
                            rsp_valid <= 1;
                        end
                        if (bit_cnt >= 7) state <= DONE;
                        else bit_cnt <= bit_cnt + 1;
                    end
                end
                DONE: begin
                    cmd_busy <= 0;
                    state <= IDLE;
                end
            endcase
        end
    end
endmodule

module sd_spi_ctrl_tb;
    logic clk=0, rst=1;
    logic [5:0] cmd; logic [31:0] cmd_arg;
    logic cmd_start, cmd_busy;
    logic [7:0] rsp_data; logic rsp_valid;
    logic spi_clk, spi_mosi, spi_miso=1;
    logic spi_cs_n;

    sd_spi_ctrl uut(.*);
    always #10 clk = ~clk;

    initial begin
        rst=1; #50; rst=0;
        $display("--- SD卡控制器测试 ---");
        // CMD0: 复位SD卡
        cmd=6'd0; cmd_arg=32'd0; cmd_start=1; #20; cmd_start=0;
        wait(!cmd_busy);
        $display("  CMD0(复位)发送完成 ✓");
        // CMD8: 检查SD卡版本
        cmd=6'd8; cmd_arg=32'h000001AA; cmd_start=1; #20; cmd_start=0;
        wait(!cmd_busy);
        $display("  CMD8(检查)发送完成 ✓");
        $display("SD卡控制器测试完成 ✓");
        #100; $finish;
    end
endmodule