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Altera_Forum's avatar
Altera_Forum
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10 years ago

Comparison between old value and new value

Hi All,

Its a very simple question but I am unable to do that. Below is my code. I want to store signal data_o_new to signal data_o_old and then compare these signals with each other and do increment or decrement until these two signals become same. data_o_new is coming from an ip. Please help me... thanks

Architechture starts here:

Begin

data_o_old <= data_o_new;

data_o <= data_o_old;

fading: PROCESS(clk)

Begin

if rising_edge(clk) then

if data_o_new > data_o_old then

data_o_old <= data_o_old + 1;

elsif data_o_new < data_o_old then

data_o_old <= data_o_old - 1;

else

data_o_old <= data_o_new;

end if;

end if;

end process;

end Architecture;

15 Replies

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  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    then why not do something like this? 

    
signal value_ref : unsigned(Nbits-1 downto 0);
signal output_ref : unsigned(Nbits-1 downto 0);
process(clk)
begin
  if rising_edge(clk) then
    value_ref <= new_value;
    if value_ref > output_ref then
      output_ref <= output_ref +1;
    elsif value_ref < output_ref then
      output_ref <= output_ref -1;
    end if;
  end if;
end process;
op <= output_ref;

    Here, the output never changes dramatically, but is gradually pulled towards your new value.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    --- Quote Start ---

    I dont want abrupt change of new value. that's why I store the new value to a signal then do increment or decrement to that signal while my signal is going to output having a smooth transition.

    --- Quote End ---

    A more practical approach is running average filter, it does not need any mults, you just add say 8 samples together then discard 3 Lsb off result.

    If you are aiming at incrementing/decrementing by 1 you may either not have enough time to catch up or you have more gaps
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    thanks tricky... I dont understand what is initial value of output_ref?? So how it can be compared

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    --- Quote Start ---

    thanks tricky... I dont understand what is initial value of output_ref?? So how it can be compared

    --- Quote End ---

    Sorry, I should have initialised it - you could do it like this:

    signal output_ref : unsigned(Nbits-1 downto 0) := (others => '0'); --or whatever value you want

    or with a reset.