mor1kx-bemicrocv/cores/uart/uart_tx.vhd

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2016-08-04 19:22:38 +02:00
-- A simple UART (TX)
-- Author : Kurisu <kurisu@shimatta.de>
-- Modifed : Markus <markus-oliver.koch@thalesgroup.com>
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
entity uart_tx is
port(
clk : in std_logic;
rst : in std_logic;
data : in std_logic_vector(7 downto 0);
byte_ready : in std_logic;
busy : out std_logic;
ckDiv : in std_logic_vector(15 downto 0);
parityEnable : in std_logic;
parityOdd : in std_logic;
twoStopBits : in std_logic;
tx : out std_logic
);
end entity uart_tx;
architecture RTL of uart_tx is
type state_t is (IDLE, START, TRANSMIT, PARITY, STOP);
signal state : state_t;
signal clkDivider : unsigned(15 downto 0);
signal data_i : std_logic_vector(7 downto 0);
signal bitCounter : integer range 0 to 7;
signal parity_calc : std_logic;
begin
txFSM : process(clk, rst, ckDiv, parityOdd) is
begin
if rst = '1' then
data_i <= x"00";
state <= IDLE;
tx <= '1';
bitCounter <= 0;
busy <= '0';
clkDivider <= unsigned(ckDiv);
parity_calc <= parityOdd;
elsif rising_edge(clk) then
busy <= '1';
if (clkDivider = 0) then
clkDivider <= unsigned(ckDiv);
else
clkDivider <= clkDivider - 1;
end if;
case state is
when IDLE =>
busy <= '0';
tx <= '1';
if byte_ready = '1' then
data_i <= data;
state <= START;
clkDivider <= unsigned(ckDiv);
bitCounter <= 0;
parity_calc <= '0';
busy <= '1';
tx <= '1';
end if;
when START =>
tx <= '0';
state <= TRANSMIT;
when TRANSMIT =>
if (clkDivider = to_unsigned(0, clkDivider'length)) then
tx <= data_i(bitCounter);
if data_i(bitCounter) = '1' then
parity_calc <= not parity_calc;
end if;
if bitCounter = 7 then
bitCounter <= 0;
if parityEnable = '1' then
state <= PARITY;
else
state <= STOP;
end if;
else
bitCounter <= bitCounter + 1;
end if;
end if;
when PARITY =>
if (clkDivider = to_unsigned(0, clkDivider'length)) then
tx <= parity_calc;
state <= STOP;
end if;
when STOP =>
if (clkDivider = to_unsigned(0, clkDivider'length)) then
tx <= '1';
bitCounter <= bitCounter + 1;
if (bitCounter = 1 and twoStopBits = '0') or (bitCounter = 2 and twoStopBits = '1') then
state <= IDLE;
end if;
end if;
end case;
end if;
end process txFSM;
end architecture RTL;