spi_protocol.v

module spi_master (
    input wire clk,
    input wire rst,
    input wire [7:0] data_in,
    input wire start,
    input wire miso,
    input wire [N-1:0] cs,  // N is the number of slaves


    
    output reg spi_clk,
    output reg mosi,
    output reg [7:0] data_out,
    output reg done
);
    parameter N = 4; // Define the number of slaves

    reg [2:0] bit_cnt;
    reg [7:0] shift_reg;
    reg [1:0] state;

    localparam IDLE = 2'b00,
               TRANSFER = 2'b01,
               DONE = 2'b10;

    always @(posedge clk or posedge rst) begin
        if (rst) begin
            spi_clk <= 0;
            mosi <= 0;
            data_out <= 0;
            done <= 0;
            bit_cnt <= 0;
            state <= IDLE;
        end else begin
            case (state)
                IDLE: begin
                    if (start) begin
                        shift_reg <= data_in;
                        bit_cnt <= 0;
                        state <= TRANSFER;
                    end
                    done <= 0;
                end

                TRANSFER: begin
                    spi_clk <= ~spi_clk;
                    if (spi_clk) begin
                        mosi <= shift_reg[7];
                        shift_reg <= {shift_reg[6:0], miso};
                        bit_cnt <= bit_cnt + 1;
                        if (bit_cnt == 7) state <= DONE;
                    end
                end

                DONE: begin
                    data_out <= shift_reg;
                    done <= 1;
                    state <= IDLE;
                end
            endcase
        end
    end
endmodule