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I2S output in VHDL

Discussion in 'Physics' started by Mathias, Oct 8, 2018.

  1. Mathias

    Mathias Guest

    I am making an I2S output in VHDL for a project. This is my first project using VHDL and the problem may be my basic VHDL understanding.

    This is my code:

    library ieee;
    use ieee.std_logic_1164.all;
    use IEEE.numeric_std.all;

    entity DE0_CV is
    port (
    CLOCK_50 : in std_logic; --clock input
    GPIO : inout std_logic_vector(35 downto 1) --IO ports
    end DE0_CV;

    architecture behave of DE0_CV is
    signal WS : std_logic; --word select for I2S --word select
    signal data_left : std_logic_vector(15 downto 0); --data for I2S
    signal data_right : std_logic_vector(15 downto 0); --data for I2S

    signal CHANNEL : std_logic; -- input from ADC, used for WS

    signal clk_div_4 : std_logic; --6.25 MHz clock
    signal clk_div_8 : std_logic; --3.125 MHz clock

    CHANNEL <= GPIO(24); -- input from ADC
    GPIO(34) <= CHANNEL; -- output to DAC


    variable cnt_4 : integer range 0 to 3 := 0;
    variable cnt_8 : integer range 0 to 7 := 0;

    if RISING_EDGE(CLOCK_50) then
    if cnt_8 = 7 then
    clk_div_8 <= NOT clk_div_8;
    cnt_8 := 0;
    cnt_8 := cnt_8 + 1;
    end if;

    if cnt_4 = 3 then
    clk_div_4 <= NOT clk_div_4;
    cnt_4 := 0;
    cnt_4 := cnt_4 + 1;
    end if;
    end if;
    end process;

    process (clk_div_8)
    variable out_bit : integer range 0 to 15 := 0;
    variable WS_state : std_logic;


    data_right <= "1111111111111111"; --test data for right channel
    data_left <="111011101111111"; --test data for right channel

    GPIO(32) <= clk_div_8; --clk for DAC

    if WS_state /= WS AND RISING_EDGE(clk_div_8) then --if WS changes state
    WS_state := WS;
    out_bit := 0; --reset out bit
    end if;

    if RISING_EDGE(clk_div_8) then
    if WS = '1' then
    GPIO(30) <= data_right(out_bit); --set data for DAC
    out_bit := out_bit + 1; --change data bit
    elsif WS = '0' then
    GPIO(30) <= data_left(out_bit); --set data for DAC
    out_bit := out_bit + 1; --change data bit
    end if;
    end if;
    end process;
    end behave;

    When using the code, the output works partly. As seen on the follwing picture, the data is delayed every second time. This is for moth left and right channel.


    How can i fix this? I don't understand why this is happening as the out_bit should reset at the same time (I think?).

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