Subversion Repositories simpcon

--

--      sc_sigdel.vhd

--

--      A simple sigma-delta ADC and PWM DAC for the SimpCon interface

--      

--      Author: Martin Schoeberl        martin@jopdesign.com

--

--

--      resources on Cyclone

--

--              xx LCs, max xx MHz

--

--

--      2006-04-16      first version

--

--      todo:

--

--

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.jop_config.all;

entity sc_sigdel is

generic (addr_bits : integer; fsamp : integer);

port (

        clk             : in std_logic;

        reset   : in std_logic;

-- SimpCon interface

        address         : in std_logic_vector(addr_bits-1 downto 0);

        wr_data         : in std_logic_vector(31 downto 0);

        rd, wr          : in std_logic;

        rd_data         : out std_logic_vector(31 downto 0);

        rdy_cnt         : out unsigned(1 downto 0);

-- io ports

        sdi                     : in std_logic;         -- input of the sigma-delta ADC

        sdo                     : out std_logic;        -- output of the sigma-delta ADC

        dac                     : out std_logic         -- output of the PWM DAC

);

end sc_sigdel;

architecture rtl of sc_sigdel is

        -- we use a 10MHz sigma-delta clock

        constant SDF            : integer := 10000000;

        constant SDTICK         : integer := (clk_freq+SDF/2)/SDF;

        signal clksd            : integer range 0 to SDTICK;

        constant CNT_MAX        : integer := (SDF+fsamp/2)/fsamp;

        signal cnt                      : integer range 0 to CNT_MAX;

        signal dac_cnt          : integer range 0 to CNT_MAX;

        signal rx_d                     : std_logic;

        signal serdata          : std_logic;

        signal spike            : std_logic_vector(2 downto 0);  -- sync in, filter

        signal sum                      : unsigned(15 downto 0);

        signal delta            : unsigned(15 downto 0);

        signal audio_in         : std_logic_vector(15 downto 0);

        signal audio_out        : std_logic_vector(15 downto 0);

        signal sample_rdy       : std_logic;

        signal sample_rd        : std_logic;

        signal sample_wr        : std_logic;

begin

        rdy_cnt <= "00";        -- no wait states

        -- we use only 16 bits

        -- bit 31 is the ready bit

        rd_data(30 downto 16) <= (others => '0');

--

--      The registered MUX is all we need for a SimpCon read.

--      The read data is stored in registered rd_data.

--

process(clk, reset)

begin

        if (reset='1') then

                rd_data(15 downto 0) <= (others => '0');

                rd_data(31) <= '0';

                sample_rd <= '0';

        elsif rising_edge(clk) then

                sample_rd <= '0';

                if rd='1' then

                        rd_data(15 downto 0) <= audio_in;

                        rd_data(31) <= sample_rdy;

                        sample_rd <= '1';

                end if;

        end if;

end process;

--

--      SimpCon write is very simple

--

process(clk, reset)

begin

        if (reset='1') then

                audio_out <= (others => '0');

                sample_wr <= '0';

        elsif rising_edge(clk) then

                sample_wr <= '0';

                if wr='1' then

                        audio_out <= wr_data(15 downto 0);

                        sample_wr <= '1';

                end if;

        end if;

end process;

--

--      Here we go with the simple sigma-delta converter:

--

process(clk, reset)

begin

        if reset='1' then

                spike <= "000";

                clksd <= 0;

                cnt <= 0;

                sum <= (others => '0');

                sample_rdy <= '0';

        elsif rising_edge(clk) then

                if clksd=0 then

                        clksd <= SDTICK-1;

                        spike(0) <= sdi;

                        spike(2 downto 1) <= spike(1 downto 0);

                        sdo <= not rx_d;

                        serdata <= rx_d;

                        if cnt=0 then

                                cnt <= CNT_MAX-1;

                                audio_in <= std_logic_vector(sum);

                                sample_rdy <= '1';

                                sum <= (others => '0');

                                -- BTW: we miss one sigma-delta sample here...

                        else

                                cnt <= cnt-1;

                                if serdata='1' then

                                        sum <= sum+1;

                                end if;

                        end if;

                else

                        clksd <= clksd-1;

                end if;

                -- reset ready flag after read

                if sample_rd='1' then

                        sample_rdy <= '0';

                end if;

        end if;

end process;

--

--      filter input (majority voting)

--

        with spike select

                rx_d <= '0' when "000",

                                '0' when "001",

                                '0' when "010",

                                '1' when "011",

                                '0' when "100",

                                '1' when "101",

                                '1' when "110",

                                '1' when "111",

                                'X' when others;

--

--      and here comes the primitive version of the

--      digital delta part - not really delta...

--              it's just a simple PWM...

--      now do it with the main clock...

--

process(clk, reset)

begin

        if reset='1' then

                delta <= (others => '0');

                dac <= '0';

                dac_cnt <= 0;

        elsif rising_edge(clk) then

                if dac_cnt=0 then

                        dac_cnt <= CNT_MAX-1;

                        delta <= unsigned(audio_out);

                else

                        dac_cnt <= dac_cnt-1;

                        dac <= '0';

                        if delta /= 0 then

                                delta <= delta-1;

                                dac <= '1';

                        end if;

                end if;

        end if;

end process;

end rtl;