verilog/rtl/jacaranda-8/UART/UART.v

// clock must be 50MHz
// baud rate 115200bps, stop bit 1bit, data 8bit, no parity, no flow control

module UART(
    input wire clk,
    input wire reset,
    input wire tx_en,
    input wire rx_en,
    input wire begin_flag,
    input wire rx,
    input wire [7:0] tx_data,
    input wire [7:0] access_addr,
    input wire reg_w_en,
    output wire tx,
    output wire[7:0] rx_data,
    output wire busy_flag,
    output wire receive_flag,
    output reg int_req,
    input wire [31:0] clk_freq
);

    parameter BAUD_RATE = 115200;

    wire [31:0] clk_count_bit;
    reg state;

    assign clk_count_bit = clk_freq / BAUD_RATE;

    always @(negedge clk) begin
        if(state == 1'b0) begin //データ待機中
            int_req <= 1'b0;
            if(receive_flag == 1'b1) begin
                state <= 1'b1;
            end else begin
                state <= state;
            end
        end else if(state == 1'b1) begin //データが来たことをCPUに伝える
            int_req <= 1'b1;
            if(access_addr == 8'd252 && reg_w_en == 1'b1) begin
                state <= 1'b0;
            end else begin
                state <= state;
            end
        end
    end
    always @(posedge reset) begin
        int_req <= 1'b0;
        state   <= 1'b0;
    end

    tx tx1(clk, reset, tx_en, begin_flag, tx_data, tx, busy_flag, clk_count_bit);
    rx rx1(clk, rx_en, rx, rx_data, receive_flag, clk_count_bit);
    
endmodule