module BUS_Con (
    input i_sys_clk,
    input i_rst_n,
    
    // SPI Interface
    input i_sclk,
    input i_mosi,
    input i_cs,
    output o_miso,          // <-- MISO Logic added here
    
    // Local Interface
    output o_rvaild,        // (Typo in original: o_rvalid)
    input i_rvaild,         // Valid signal from Backend (Data is ready)
    input i_wvaild,
    output o_wready,
    input i_reg_busy,
    input [23:0] i_rdata,   // Data from Backend to send to Master
    output o_wr,
    output o_cmd_vaild,
    output [23:0] o_data,
    output [6:0] o_addr,
    output o_err
);

    // --- 1. Synchronization ---
    reg [1:0] cs_sync;
    reg [1:0] sclk_sync;
    reg [1:0] mosi_sync;
    
    wire cs_active;
    wire cs_rise;
    wire sclk_rise; // For Sampling MOSI
    wire sclk_fall; // For Shifting MISO
    wire mosi_data;
	

    always @(posedge i_sys_clk) begin
        if (!i_rst_n) begin
            cs_sync   <= 2'b11;
            sclk_sync <= 2'b00;
            mosi_sync <= 2'b00;
        end else begin
            cs_sync   <= {cs_sync[0], i_cs};
            sclk_sync <= {sclk_sync[0], i_sclk};
            mosi_sync <= {mosi_sync[0], i_mosi};
        end
    end

    assign cs_active = ~cs_sync[1]; 
    assign cs_rise   = (!cs_sync[1] && cs_sync[0]); 
    
    // SPI Mode 0: Sample MOSI on Rising, Shift MISO on Falling
    assign sclk_rise = (!sclk_sync[1] && sclk_sync[0]); 
    assign sclk_fall = (sclk_sync[1] && !sclk_sync[0]); // Logic for MISO
    assign mosi_data = mosi_sync[1];

    // --- 2. MOSI (Receive) Logic ---
    reg [31:0] recv_reg;
    reg [5:0]  bit_cnt;
    reg        data_ready;
    reg        err_flag;
	reg [1:0] state;
	//
	reg [31:0] tx_buffer;  // Holds data waiting for the next CS Low
    reg [31:0] miso_shift; // The actual shifter
    // Output Registers
    reg [6:0]  addr_out;
    reg [23:0] data_out;
    reg        wr_out;
    reg        cmd_valid_out;
	
	//
	localparam IDLE      = 2'b00;
    localparam CMD_SENT  = 2'b01;
    localparam WAIT_BUSY = 2'b10;
    localparam DONE      = 2'b11;
    

    always @(posedge i_sys_clk) begin
        if (!i_rst_n) begin
            recv_reg      <= 32'd0;
            bit_cnt       <= 6'd0;
            data_ready    <= 1'b0;
            err_flag      <= 1'b0;
        end 
		else begin
            data_ready <= 1'b0; 

            if (cs_active) begin
                if (sclk_rise) begin
                    recv_reg <= {recv_reg[30:0], mosi_data}; 
                    bit_cnt  <= bit_cnt + 1'b1;
                end
				else if (cs_rise) begin
					if (bit_cnt == 6'd32) begin
						data_ready <= 1'b1;
						err_flag   <= 1'b0;
						bit_cnt <= 6'd0;
					end 
					else if (bit_cnt != 0) begin
						err_flag   <= 1'b1;
						bit_cnt <= 6'd0;
                        recv_reg <= 'd0;
					end
				end
            end
            if (state == DONE) begin
                recv_reg <= 'd0;
            end
        end
    end

    // --- 3. MISO (Transmit) Logic ---
    // Protocol: We shift out 32 bits. 
    // Format: [8 bit Status/Padding] + [24 bit i_rdata]
    

    // Capture data from backend when valid
    always @(posedge i_sys_clk) begin
        if (!i_rst_n) begin
            tx_buffer <= 32'd0;
        end else begin
            // If backend provides valid read data, store it.
            // We pad the top 8 bits with Zeros (or you can put status flags here)
            if (i_rvaild) begin
                tx_buffer <= {8'h00, i_rdata}; 
            end
        end
    end

    // Shift data out
    always @(posedge i_sys_clk) begin
        if (!i_rst_n) begin
            miso_shift <= 32'd0;
        end else begin
            if (!cs_active) begin
                // Pre-load the shifter while CS is High
                // This ensures Bit 31 is ready BEFORE the first clock edge
                miso_shift <= tx_buffer;
            end else begin
                // Shift on Falling Edge (Master samples on Rising)
                if (sclk_fall) begin
                    miso_shift <= {miso_shift[30:0], 1'b0};
                end
            end
        end
    end

    // Tri-state MISO when CS is high (optional, usually good practice)
    // If your board doesn't need tristate, just use: assign o_miso = miso_shift[31];
    assign o_miso = (cs_active) ? miso_shift[31] : 1'bz;

    // --- 4. Register Control FSM ---

    

    always @(posedge i_sys_clk) begin
        if (!i_rst_n) begin
            state         <= IDLE;
            cmd_valid_out <= 1'b0;
            addr_out      <= 7'd0;
            data_out      <= 24'd0;
            wr_out        <= 1'b0;
        end else begin
            case (state)
                IDLE: begin
                    if (data_ready) begin
                        addr_out      <= recv_reg[30:24];
                        data_out      <= recv_reg[23:0];
                        wr_out        <= recv_reg[31];
                        
                        if (!i_reg_busy) begin
                            cmd_valid_out <= 1'b1;
                            state         <= CMD_SENT;
                        end else begin
                            state         <= WAIT_BUSY;
                        end
                    end
                end

                WAIT_BUSY: begin
                    if (!i_reg_busy) begin
                        cmd_valid_out <= 1'b1;
                        state         <= CMD_SENT;
                    end
                end

                CMD_SENT: begin
                    cmd_valid_out <= 1'b0;
                    state         <= DONE;
                end

                DONE: begin
                    if (!i_reg_busy) begin
                        state <= IDLE;
                        addr_out <= 'd0;
                        data_out <= 'd0;
                        wr_out <= 'd0;
                    end
                end
            endcase
        end
    end

    assign o_addr      = addr_out;
    assign o_data      = data_out;
    assign o_wr        = wr_out;
    assign o_cmd_vaild = cmd_valid_out;
    assign o_err       = err_flag;
    assign o_wready    = (state == IDLE); 
    
    // Pass through unused signal or hook it up if needed
    assign o_rvaild    = 1'b0; 

endmodule