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--! Baud generator

--! http://www.fpga4fun.com/SerialInterface.html

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_arith.all;

use ieee.numeric_std.all;

--! Use CPU Definitions package

use work.pkgDefinitions.all;

entity baud_generator is

    Port ( rst : in STD_LOGIC;

                          clk : in  STD_LOGIC;

           cycle_wait : in  STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

                          baud_oversample : out std_logic;

           baud : out  STD_LOGIC);

end baud_generator;

architecture Behavioral of baud_generator is

signal genTick : std_logic;

signal genTickOverSample : std_logic;

begin

        process (rst, clk, cycle_wait)

        variable wait_clk_cycles : STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

        variable half_cycle : STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

        begin

                if rst = '1' then

                        wait_clk_cycles := (others => '0');

                        half_cycle := '0' & cycle_wait(cycle_wait'high downto 1);

                        genTick <= '0';

                elsif rising_edge(clk) then

                        -- Just decremented the cycle_wait by one because genTick would be updated on the next cycle

                        -- and we really want to bring genTick <= '1' when (wait_clk_cycles = cycle_wait)

                        if wait_clk_cycles = (cycle_wait - conv_std_logic_vector(1, nBitsLarge)) then

                                genTick <= '1';

                                wait_clk_cycles := (others => '0');

                        else

                                wait_clk_cycles := wait_clk_cycles + conv_std_logic_vector(1, nBitsLarge);

                                -- If we're at half of the cycle

                                if wait_clk_cycles = half_cycle then

                                        genTick <= '0';

                                end if;

                        end if;

                        -- Avoid creation of transparent latch (By default the VHDL will create an register for vectors that are assigned only in one

                        -- ocasion of a (if, case) instruction

                        half_cycle := '0' & cycle_wait(cycle_wait'high downto 1);

                end if;

        end process;

        baud <= genTick;

        baud_oversample <= genTickOverSample;

        -- Process to generate the overclocked (8x) sample

        process (rst, clk, cycle_wait)

        variable wait_clk_cycles : STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

        variable half_cycle : STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

        variable cycle_wait_oversample : STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

        begin

                if rst = '1' then

                        wait_clk_cycles := (others => '0');

                        -- Divide cycle_wait by 4

                        --cycle_wait_oversample := '0' & cycle_wait(cycle_wait'high downto 1);                  

                        --cycle_wait_oversample := '0' & cycle_wait_oversample(cycle_wait_oversample'high downto 1);

                        cycle_wait_oversample := "00" & cycle_wait(cycle_wait'high downto 2);   -- Shift right by 2                     

                        -- Half of cycle_wait_oversample

                        half_cycle := '0' & cycle_wait_oversample(cycle_wait_oversample'high downto 1); -- Shift right by 1

                        genTickOverSample <= '0';

                elsif rising_edge(clk) then

                        -- Just decremented the cycle_wait by one because genTick would be updated on the next cycle

                        -- and we really want to bring genTick <= '1' when (wait_clk_cycles = cycle_wait)

                        if wait_clk_cycles = (cycle_wait_oversample - conv_std_logic_vector(1, nBitsLarge)) then

                                genTickOverSample <= '1';

                                wait_clk_cycles := (others => '0');

                        else

                                wait_clk_cycles := wait_clk_cycles + conv_std_logic_vector(1, nBitsLarge);

                                -- If we're at half of the cycle

                                if wait_clk_cycles = half_cycle then

                                        genTickOverSample <= '0';

                                end if;

                        end if;

                        -- Avoid creation of transparent latch (By default the VHDL will create an register for vectors that are assigned only in one

                        -- ocasion of a (if, case) instruction

                        cycle_wait_oversample := "00" & cycle_wait(cycle_wait'high downto 2);

                        half_cycle := '0' & cycle_wait_oversample(cycle_wait_oversample'high downto 1);

                end if;

        end process;

end Behavioral;