library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;
 
entity transfer is
    generic(framlent:integer:=8);
    Port (bclkt,resett,xmit_cmd_p:in std_logic;                       --定義輸入輸出信號
          txdbuf:in std_logic_vector(7 downto 0):="11001010";
          txd:out std_logic;
          txd_done:out std_logic);
end transfer;
 
architecture behavioral of transfer is
type states is (x_idle,x_start,x_wait,x_shift,x_stop);                 --定義個子狀態
signal state:states:=x_idle;
signal tcnt:integer:=0;
begin
 
process(bclkt,resett,xmit_cmd_p,txdbuf)                            --主控時序、組合進程
variable xcnt16:std_logic_vector(4 downto 0):="00000";             --定義中間變量
variable xbitcnt:integer:=0;
variable txds:std_logic;
 
begin 
  if resett='1' then                                                 --復位
     state<=x_idle; txd_done<='0'; txds:='1';
  elsif rising_edge(bclkt) then
     case state is
           when x_idle=>if xmit_cmd_p='1' then state<=x_start; txd_done<='0';                                 
                             else state<=x_idle;                  --狀態1，等待數據幀發送命令
                             end if;
       when x_start=>if xcnt16>="01111" then state<=x_wait; xcnt16:="00000";
                                 else xcnt16:=xcnt16+1; txds:='0'; state<=x_start;
                                     end if;                          --狀態2，發送信號至起始位
       when x_wait=>if xcnt16>="01110" then
                            if xbitcnt=framlent then state<=x_stop; xbitcnt:=0;
                                            else state<=x_shift;
                                            end if;
                                        xcnt16:="00000";
                         else xcnt16:=xcnt16+1; state<=x_wait;
                                     end if;                     --狀態3，等待狀態
       when x_shift=>txds:=txdbuf(xbitcnt); xbitcnt:=xbitcnt+1; state<=x_wait;                                                                    --狀態4，將待發數據進行并串轉換
       when x_stop=>if xcnt16>="01111" then
                                    if xmit_cmd_p='0' then state<=x_idle; xcnt16:="00000";
                                            else xcnt16:=xcnt16; state<=x_stop;
                                            end if; txd_done<='1';
                                 else xcnt16:=xcnt16+1; txds:='1'; state<=x_stop;
                                 end if;                      --狀態5，停止位發送狀態
               when others=>state<=x_idle;
       end case;         
  end if;
  txd<=txds;
end process;
 
end behavioral;