MMC/rtl/peripherals/UART_RX.v

module UART_RX (
    input             clk      ,
    input             clk_uart ,
    input             RSTn     ,
    input             RXD      ,
    output reg  [7:0] data     ,
    output wire       interrupt,
    output wire       bps_en
);

//shift register
    reg [7:0] shift_reg;
    always@(posedge clk) begin
        if(~RSTn) shift_reg <= 8'hff;
        else shift_reg <= {RXD,shift_reg[7:1]};
    end

    wire re_start;
    assign re_start = (shift_reg == 8'h0f) ? 1'b1 : 1'b0;

// recive counter
    reg       counter_en;
    reg [3:0] counter   ;

    always@(posedge clk or negedge RSTn) begin
        if(~RSTn) counter_en <= 1'b0;
        else if(re_start&&(~counter_en)) counter_en <= 1'b1;
        else if(counter == 4'h9) counter_en <= 1'b0;ß
    end

    always@(posedge clk or negedge RSTn) begin
        if(~RSTn) counter <= 4'h0;
        else if(counter_en) begin
            if(clk_uart) counter <= counter + 1'b1;
            else if(counter == 4'h9) counter <= 4'h0;
        end
    end

    assign bps_en = counter_en;

// RXD re
    always@(posedge clk or negedge RSTn) begin
        if(~RSTn) data <= 8'h00;
        else if(counter_en) begin
            if(clk_uart && (counter <= 4'h8)) data[counter-1] <= RXD;
        end
    end

//interrupt
    assign interrupt = (counter == 4'h9) ? 1'b1 : 1'b0;


endmodule