Re: [oc] I2C slave source help

[Colin Marquardt <c.marquardt@alcatel.de>]

ckh827@hotmail.com writes:

> could somebody give me some comments on the I2C slave model below? it
> got ping only 1 out of 20.  I tried so hard to debug it and has no
> luck.  could somebody help me out.  

I took 7 minutes to clean up the style a bit and made some coding
style comments, without even trying to run it through a compiler
or understanding what it is actually doing.  Maybe that helps you
already. Check for "!!!" and "FIXME", and do a diff against your
original code to see what I changed.


entity backlightI2C is
   port (sda     : inout std_logic := 'Z';
         scl     : in    std_logic;          -- !!! why was this inout?
         dataout : out   std_logic_vector(7 downto 0));
end backlightI2C;

-- !!! architecture is not really behavioral but more RTL:
architecture Behavioral of backlightI2C is

   signal sda_o        : std_logic;
   signal clr_start    : std_logic;
   signal start        : std_logic;
   signal d_start      : std_logic;
   signal startnow     : std_logic;
   signal d_startnow   : std_logic;
   signal startnow1    : std_logic;
   signal stop         : std_logic;
   signal stopnow      : std_logic;
   signal clkstop      : std_logic;
   signal sigSDA       : std_logic;
   signal selected     : std_logic;
   signal DATA         : std_logic_vector(7 downto 0);
   
begin

   sdacheck : process(sda)
   begin
      ---------------------------------------------
      if sda'event then
         if (scl = '1' and sda = '0') then
            startnow <= '1';
         elsif (scl = '1' and sda = '1') then
            stopnow <= '1';
            -- FIXME: else missing
         end if;
      end if;
   end process;

   sclkk : process(scl)
      variable count : natural := 0;
   begin
      -- !!! no reset?
      if (scl'event and scl = '0') then
         if (startnow = '1') then
            start <= '1';
         elsif (stopnow = '1') then
            start <= '0';
            count := 0;
            -- FIXME: missing else
         end if;

         -- FIXME: missing default assignments (e.g. selected)
         if (start = '1') then
            case count is
               when 0 => data(7) <= sda;
                         count := 1;
                         start <= '1';

               when 1 => data(6) <= sda;
                         count := 2;
                         start <= '1';
                         
               when 2 => data(5) <= sda;
                         count := 3;
                         start <= '1';

               when 3 => data(4) <= sda;
                         count := 4;
                         start <= '1';
                         
               when 4 => data(3) <= sda;
                         count := 5;
                         start <= '1';
                         
               when 5 => data(2) <= sda;
                         count := 6;
                         start <= '1';
                         
               when 6 => data(1) <= sda;
                         count := 7;
                         start <= '1';

               when 7 => data(0) <= sda;
                         count := 8;
                         start <= '1';
                         
               when 8 =>
                  start    <= '0';
                  count    := 0;
                  if (data = "11100001") then
                     selected <= '1';
                     sda_o    <= '0';
                  else
                     sda_o <= 'Z';
                  end if;

               when others =>
                  count := 0;
                  start <= '0';
                  sda_o <= 'Z';

            end case;
         end if;

         if sda_o = '0' then
            sda <= '0';
         else
            sda <= 'Z';
         end if;

      end if;

   end process;

end Behavioral;
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