MMC/rtl/peripherals/UART_TX.v

module UART_TX (
    input             clk     ,
    input             clk_uart,
    input             RSTn    ,
    input       [7:0] data    ,
    input             tx_en   ,
    output reg        TXD     ,
    output wire       state   ,
    output wire       bps_en
);

//FIFO 8bit-16depth
    wire       FIFOrd_en;
    wire       FIFOwr_en;
    wire [7:0] FIFOdata ;
    wire       FIFOempty;
    wire       FIFOfull ;
    FIFO FIFO (
        .clock(clk      ),
        .sclr (RSTn     ),
        .rdreq(FIFOrd_en),
        .wrreq(FIFOwr_en),
        .full (FIFOfull ),
        .empty(FIFOempty),
        .data (data     ),
        .q    (FIFOdata )
    );

//FIFO write control
    assign FIFOwr_en = (~FIFOfull) & tx_en;

    assign state = FIFOfull;

//UART TX
    reg       counter_en;
    reg [3:0] counter   ;

    wire trans_finish;
    assign trans_finish = (counter == 4'hb);

    wire trans_start;
    assign trans_start = (~FIFOempty) & (~counter_en);

    always@(posedge clk or negedge RSTn) begin
        if(~RSTn) counter_en <= 1'b0;
        else if(trans_start) counter_en <= 1'b1;
        else if(trans_finish) counter_en <= 1'b0;
    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(trans_finish) counter <= 4'h0;
        end
    end

    assign bps_en = counter_en;

    wire [9:0] data_formed;

    assign data_formed = {1'b1,FIFOdata,1'b0};

    always@(posedge clk or negedge RSTn) begin
        if(~RSTn) TXD <= 1'b1;
        else if(counter_en) begin
            if(clk_uart && (counter <= 4'h9)) TXD <= data_formed[counter];
        end else TXD <= 1'b1;
    end

//FIFO read control
    assign FIFOrd_en = (~FIFOempty) & trans_finish;

endmodule