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Altera_Forum's avatar
Altera_Forum
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16 years ago

Error (10818): (does not hold its value outside the clock edge)

Hello,

I am trying to build a pulse counter that shoud be connected to an external switch and count the times the user push the button.

moreover i need to output: result,result+1,result +2.

i have written the next code and it works graet on model sim but quartus dosent like it, i an getting the error:

Error (10818): Can't infer register for "q2_int[X]" at counter.vhd(32) because it does not hold its value outside the clock edge.

for every bit, someone has an idea how to solve it?

the code is:

--- Quote Start ---

library ieee;

use ieee.std_logic_1164.all;

use IEEE.std_logic_unsigned.all;

entity counter is port (

load : in std_logic;

q,q1,q2 : buffer std_logic_vector (4 downto 0));

end entity;

architecture rtl of counter is

signal q_int : std_logic_vector (4 downto 0):="00000";

signal q1_int : std_logic_vector (4 downto 0):="00000";

signal q2_int : std_logic_vector (4 downto 0):="00000";

begin

process (load,q_int)

begin

if (q_int="00000") then

q<="LLLLL";

q1_int<="LLLLH";

q2_int<="LLLHL";

else

end if;

if (rising_edge(load)) then

q_int <= q_int + 1;

q1_int<=q1_int + 1;

q2_int<=q2_int + 1;

end if;

end process;

q <= q_int;

q1 <= q1_int;

q2 <= q2_int;

end rtl;

--- Quote End ---

thanks alot

Pini Sberro

6 Replies

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

    The recommended way of writing a process that can be synthesized is the following: 

    process(clock,reset)
begin
  if (reset = '1') then
    -- reset conditions
  elsif (rising_edge(clock)) then
    -- clocked operations
  end if;
end process;
    The reset part is optional, but recommended.

    I think that in your case the synthesizer is confused by your first if in the process and doesn't know what to do with it. It isn't a reset condition, and you are assigning signal values outside of a clock edge. You should change your first part as a real reset condition, or scrap it and give correct initial values to q_int, q1_int and q2_int. You could also keep only one counter and assign its value +1 or +2 to the correct output.

    You shouldn't need to use the L and H values if you do everything inside the clocked part of the process.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    Basically there are 2 problems:

    1. It thinks "load" is a clock. On the edge of load, Q_int is updated along with Q1_int and Q2_int

    2. Now that Q_int has changed, it changes Q1 and Q2 int to fixed values, so now these things that were clocked, are no longer clocked.

    Now, because you dont have a clock - you dont have to do your logic inside a process. But I think you really could use a clock, like Daixiwen suggests.

    One big issue though, appears to be that you're trying to write the code without understanding the hardware that you're describing.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    Thank you very much.

    its working!

    Tricky, about ur comment:

    "

    appears to be that you're trying to write the code without understanding the hardware that you're describing

    "

    it was very usfull for me so thanks again
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    14 years ago

    I am having the same problem too - Error 10818 (does not hold its value outside the clock edge) and 10822 (couldn't implement registers for assignment on this clock edge) but i cant understand what changes do i need to do.

    I am trying to build a Counter that count the time user successfully catches a number 8.

    If it is, then a logic '1' will be sent out and a signal will record the times of success events and sent out too.

    I have another question is "can i use rising_edge to detect any change of logic value for any time of signal ? std_logic / unsigned / integer .. etc ....

    Here is the code

    --- Quote Start ---

    library IEEE;

    use IEEE.std_logic_1164.all;

    use IEEE.std_logic_arith.all;

    entity catch is

    port (

    PUSH : in std_logic;

    COMP : in unsigned(3 downto 0);

    RST : in std_logic;

    INC_FREQ : out integer range 1 to 10;

    SCORE_COUNT : out std_logic

    );

    end catch;

    architecture catch_arch of catch is

    signal var_INC_FreQ : integer range 1 to 10;

    begin

    process (RST,PUSH,COMP)

    begin

    if RST = '0' then

    var_INC_FREQ <= 1;

    elsif rising_edge(PUSH) then

    if COMP = 8 then

    SCORE_COUNT <= '1';

    var_INC_FREQ <= var_INC_FREQ + 1;

    end if;

    else

    SCORE_COUNT <= '0';

    end if;

    end process;

    INC_FREQ <= var_INC_FREQ;

    end catch_arch;

    --- Quote End ---

    Thanks alot !