Uart.V 串口 fpga

http://home.eeworld.com.cn/my/space-uid-210489-blogid-66899.html

module uart #(
    parameter clk_freq = 50000000,
    parameter baud = 9600
) (
    input sys_clk,
    input sys_rst,

    output rx_irq,
    output tx_irq,

    input uart_rx,
    output uart_tx
);

wire [7:0] rx_data;
reg [7:0] tx_data;
reg tx_wr;

always @(posedge sys_clk)
begin
    if (rx_irq)
    begin
    tx_data <= rx_data;
    tx_wr <= 1'b1;
    end
    else
    begin
    tx_wr <= 1'b0;
    end
end

uart_transceiver transceiver(
    .sys_clk(sys_clk),
    .sys_rst(sys_rst),

    .uart_rx(uart_rx),
    .uart_tx(uart_tx),

    .divisor(clk_freq/baud/16),

    .rx_data(rx_data),
    .rx_done(rx_irq),

    .tx_data(tx_data),
    .tx_wr(tx_wr),
    .tx_done(tx_irq)
);

endmodule

  uart_transceiver.v

  /*

 * Milkymist VJ SoC
 * Copyright (C) 2007, 2008, 2009, 2010 Sebastien Bourdeauducq
 * Copyright (C) 2007 Das Labor
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

module uart_transceiver(
    input sys_rst,
    input sys_clk,

    input uart_rx,
    output reg uart_tx,

    input [15:0] divisor,

    output reg [7:0] rx_data,
    output reg rx_done,

    input [7:0] tx_data,
    input tx_wr,
    output reg tx_done
);

//-----------------------------------------------------------------
// enable16 generator
//-----------------------------------------------------------------
reg [15:0] enable16_counter;

wire enable16;
assign enable16 = (enable16_counter == 16'd0);

always @(posedge sys_clk) begin
    if(sys_rst)
        enable16_counter <= divisor - 16'b1;
    else begin
        enable16_counter <= enable16_counter - 16'd1;
        if(enable16)
            enable16_counter <= divisor - 16'b1;
    end
end

//-----------------------------------------------------------------
// Synchronize uart_rx
//-----------------------------------------------------------------
reg uart_rx1;
reg uart_rx2;

always @(posedge sys_clk) begin
    uart_rx1 <= uart_rx;
    uart_rx2 <= uart_rx1;
end

//-----------------------------------------------------------------
// UART RX Logic
//-----------------------------------------------------------------
reg rx_busy;
reg [3:0] rx_count16;
reg [3:0] rx_bitcount;
reg [7:0] rx_reg;

always @(posedge sys_clk) begin
    if(sys_rst) begin
        rx_done <= 1'b0;
        rx_busy <= 1'b0;
        rx_count16  <= 4'd0;
        rx_bitcount <= 4'd0;
    end else begin
        rx_done <= 1'b0;

        if(enable16) begin
            if(~rx_busy) begin // look for start bit
                if(~uart_rx2) begin // start bit found
                    rx_busy <= 1'b1;
                    rx_count16 <= 4'd7;
                    rx_bitcount <= 4'd0;
                end
            end else begin
                rx_count16 <= rx_count16 + 4'd1;

                if(rx_count16 == 4'd0) begin // sample
                    rx_bitcount <= rx_bitcount + 4'd1;

                    if(rx_bitcount == 4'd0) begin // verify startbit
                        if(uart_rx2)
                            rx_busy <= 1'b0;
                    end else if(rx_bitcount == 4'd9) begin
                        rx_busy <= 1'b0;
                        if(uart_rx2) begin // stop bit ok
                            rx_data <= rx_reg;
                            rx_done <= 1'b1;
                        end // ignore RX error
                    end else
                        rx_reg <= {uart_rx2, rx_reg[7:1]};
                end
            end
        end
    end
end

//-----------------------------------------------------------------
// UART TX Logic
//-----------------------------------------------------------------
reg tx_busy;
reg [3:0] tx_bitcount;
reg [3:0] tx_count16;
reg [7:0] tx_reg;

always @(posedge sys_clk) begin
    if(sys_rst) begin
        tx_done <= 1'b0;
        tx_busy <= 1'b0;
        uart_tx <= 1'b1;
    end else begin
        tx_done <= 1'b0;
        if(tx_wr) begin
            tx_reg <= tx_data;
            tx_bitcount <= 4'd0;
            tx_count16 <= 4'd1;
            tx_busy <= 1'b1;
            uart_tx <= 1'b0;
`ifdef SIMULATION
            $display("UART:Â %c", tx_data);
`endif
        end else if(enable16 && tx_busy) begin
            tx_count16  <= tx_count16 + 4'd1;

            if(tx_count16 == 4'd0) begin
                tx_bitcount <= tx_bitcount + 4'd1;

                if(tx_bitcount == 4'd8) begin
                    uart_tx <= 1'b1;
                end else if(tx_bitcount == 4'd9) begin
                    uart_tx <= 1'b1;
                    tx_busy <= 1'b0;
                    tx_done <= 1'b1;
                end else begin
                    uart_tx <= tx_reg[0];
                    tx_reg <= {1'b0, tx_reg[7:1]};
                end
            end
        end
    end
end

endmodule