Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
17 years ago

quartus error

Hello.

I am trying to compile some VHDL code (deserializer) in Quartus II and the compiler returns me a bunch of errors:

Error (10818): Can't infer register for "qs[0]" at deserializer.vhd(101) because it does not hold its value outside the clock edge

for all the qs[ ]

I tryed to compile the same source in modelsim and it worked fine. Althought i can make a schematic file or write it in AHDL and it will work as VHDL code. So i cannot understand why the VHDL file is not syntesizable. Maybe someone can help me with it.

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.numeric_std.all;

entity deserializer is

--- {{{ interface signals declaration

port(

--- {{{ system clock

sclk : in std_logic; -- 270 Mhz deserializer clock. Deserializes data into 2-bit words.

pclk : in std_logic; -- 27 Mhz word rate clock.

reset : in std_logic; -- Async active high reset

--- }}}

--- {{{ interface 1

data_in : in std_logic; -- 10-bit parallel unscrambled data in

--- }}}

--- {{{ interface 2

q : out std_logic_vector(9 downto 0) -- 1-bit deserialized data output.

--data_10b_out : out std_logic_vector(9 downto 0); -- 10-bit parallel unscrambled data in

--- }}}

);

end deserializer;

--- }}}

--- {{{ RTL Architecture Declaration

architecture STRUCTURE of deserializer is

--- {{{ internal signals declaration

signal inc : std_logic_vector (3 downto 0):="0000";

signal qs : std_logic_vector(9 downto 0) :="0000000000" ;

--- }}}

begin -- rtl

--- {{{ sequential process

-- purpose: sequential process

-- type : sequential

-- inputs : sclk, rst

-- outputs: q

sync_count : process(sclk,pclk, reset)

--variable inc : std_logic_vector (3 downto 0);

begin

if (reset = '1') then

qs <= "0000000000";

elsif rising_edge(pclk) then

q<=qs ;

-- pour pouvoir synthètiser le bloc avec quartus

end if;

if (rising_edge(sclk)) then

inc <= inc+1;

if (inc = "1001") then -- return to '0' when inc achieve '9'

inc <= "0000";

end if;

case inc is -- i is the counter in 0 to 9

when "0000" => qs(9) <= data_in;

when "0001" => qs(8) <= data_in;

when "0010" => qs(7) <= data_in;

when "0011" => qs(6) <= data_in;

when "0100" => qs(5) <= data_in;

when "0101" => qs(4) <= data_in;

when "0110" => qs(3) <= data_in;

when "0111" => qs(2) <= data_in;

when "1000" => qs(1) <= data_in;

when "1001" => qs(0) <= data_in;

when others => qs <= "0000000000";

end case;

end if;

end process sync_count;

--- }}}

end STRUCTURE;

thank you for your help

10 Replies

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

    You are not supposed to use two clk edges per process, only one per process.

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

    i'm used to use two clk in the same process and it works...i can show you the example of the serializer which i coded in vhdl using two clk in the same process:

    library ieee;

    use ieee.std_logic_1164.all;

    use ieee.std_logic_unsigned.all;

    use ieee.numeric_std.all;

    entity serializer is

    --- {{{ interface signals declaration

    port(

    --- {{{ system clock

    sclk : in std_logic; -- 270 Mhz deserializer clock. Deserializes data into 2-bit words.

    pclk : in std_logic; -- 27 Mhz word rate clock.

    reset : in std_logic; -- Async active high reset

    --- }}}

    --- {{{ interface 1

    data10b : in std_logic_vector(9 downto 0); -- 10-bit parallel unscrambled data in

    --- }}}

    --- {{{ interface 2

    data_out1 : out std_logic

    -- 1-bit deserialized data output.

    --data_10b_out : out std_logic_vector(9 downto 0); -- 10-bit parallel unscrambled data in

    --- }}}

    );

    end serializer;

    --- }}}

    --- {{{ RTL Architecture Declaration

    architecture STRUCTURE of serializer is

    --- {{{ internal signals declaration

    --signal en : std_logic;

    signal data10s : std_logic_vector(9 downto 0); -- 10-bit parallel unscrambled data in

    --- }}}

    SIGNAL index : integer := 9;

    begin -- rtl

    --- {{{ sequential process

    -- purpose: sequential process

    -- type : sequential

    -- inputs : sclk, rst

    -- outputs: q

    sync_count : process(sclk,pclk, reset)

    BEGIN

    if (reset = '1') then data10s <= "0000000000";

    elsif rising_edge(pclk) then

    data10s <= data10b;

    -- inc:="0000";-- pour pouvoir synthètiser le bloc avec quartus

    end if;

    if (rising_edge(sclk)) then

    data_out1 <= data10s(index);

    index <= index - 1;

    if index = 0 then

    index <= 9;

    end if;

    end if;

    end process sync_count;

    --- }}}

    end STRUCTURE;

    so i don't think it doesn't work because of the two clk in the same process..

    what do you think?
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    --- Quote Start ---

    You are not supposed to use two clk edges per process

    --- Quote End ---

    It's something similar. Exactly, the problem is, that qs <= "0000000000"; must be mutual exclusive to the other qs[] assignments. The code should look like this:

    --- Quote Start ---

    if (reset = '1') then

    qs <= "0000000000";

    elsif (rising_edge(sclk)) then

    end if;

    --- Quote End ---

    It is basically allowed, to have multiple clock sensitive blocks in a process, but it doesn't make sense. The code is much clearer with only one clock sensitive condition in a process.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    You may have escaped once but not anymore.

    I hav never heard of two edge process in synthesis VHDL.

    It is al too easy to break it up.

    additionally, you can use constrained integer counter then just say:

    qs(count) <= data_in; -- no need for case
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    Also consider this:

    you can use the fast clk only 270MHz and then say:

    q(count) <= data_in; -- no need for double register

    your module can just read input on the counter i.e. in place of the parallel clk 27MHz - assuming it is synchronised to 270

    what is left is care with word boundaries
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    sorry but i still have a little problem;

    my new code is:

    ibrary ieee;

    use ieee.std_logic_1164.all;

    use ieee.std_logic_unsigned.all;

    use ieee.numeric_std.all;

    entity deserializer is

    --- {{{ interface signals declaration

    port(

    --- {{{ system clock

    sclk : in std_logic; -- 270 Mhz deserializer clock. Deserializes data into 2-bit words.

    pclk : in std_logic; -- 27 Mhz word rate clock.

    reset : in std_logic; -- Async active high reset

    --- }}}

    --- {{{ interface 1

    data_in : in std_logic; -- 10-bit parallel unscrambled data in

    --- }}}

    --- {{{ interface 2

    q : out std_logic_vector(9 downto 0) -- 1-bit deserialized data output.

    --data_10b_out : out std_logic_vector(9 downto 0); -- 10-bit parallel unscrambled data in

    --- }}}

    );

    end deserializer;

    --- }}}

    --- {{{ RTL Architecture Declaration

    architecture STRUCTURE of deserializer is

    --- {{{ internal signals declaration

    signal inc : std_logic_vector (3 downto 0):="0000";

    signal qs : std_logic_vector(9 downto 0) :="0000000000" ;

    --- }}}

    begin -- rtl

    --- {{{ sequential process

    -- purpose: sequential process

    -- type : sequential

    -- inputs : sclk, rst

    -- outputs: q

    sync_count : process(sclk,pclk, reset)

    --variable inc : std_logic_vector (3 downto 0);

    begin

    if rising_edge(pclk) then

    q<=qs ;

    inc<="0000"; -- <--this coz me a problem in compilation (depends on differents clock edge)..where should i write it?

    end if;

    -- pour pouvoir synthètiser le bloc avec quartus

    if (reset = '1') then

    qs <= "0000000000";

    elsif (rising_edge(sclk)) then

    inc <= inc+1;

    if (inc = "1001") then -- return to '0' when inc achieve '9'

    inc <= "0000";

    end if;

    case inc is -- i is the counter in 0 to 9

    when "0000" => qs(9) <= data_in;

    when "0001" => qs(8) <= data_in;

    when "0010" => qs(7) <= data_in;

    when "0011" => qs(6) <= data_in;

    when "0100" => qs(5) <= data_in;

    when "0101" => qs(4) <= data_in;

    when "0110" => qs(3) <= data_in;

    when "0111" => qs(2) <= data_in;

    when "1000" => qs(1) <= data_in;

    when "1001" => qs(0) <= data_in;

    when others => qs <= "0000000000";

    end case;

    end if;

    end process sync_count;

    --- }}}

    end STRUCTURE;

    how can i get inc="0000" at every rising edge of the pclk, because i would beginig counting at this rising of pclk clock?

    thank you
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    i forget to mention that without the red line the code works but don't do the real function

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

    Hi,

    try something like this code:

    serializer 

    
signal clk27_d : std_logic;
signal count : integer range 0 to 9;
 
process(reset,clk270)
begin
if reset = '1' then
   q <=  '0';
   clk27_d <= '0';
   count <= 0;
elsif rising_edge(clk270) then
 
   clk27_d <= clk_27; -- for word boundary detection
 
   if clk27 = '1' and clk27_d = '0' then
      count <= 1;
   elsif count = 9 then
      count <= 0;
   else
      count <= count + 1;
   end if;
 
   q <= data_in(count);
 
end if;
end process;
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    17 years ago

    Note above code is a serilizer. You can do a desrializer on same basis.

    I possibly got mixed up with serializer/deserilizer

    important note:

    Your desrialiser will not work since there is no indication of word beginning. You must send a signal from serialiser to indicate that, send it with the first bit. or use clk27 edge if properly aligned with data transition.

    desrialiser 

    
signal clk27_d : std_logic;
signal count : integer range 0 to 9;
 
process(reset,clk270)
begin
if reset = '1' then
   q <=  (others => '0');
   clk27_d <= '0';
   count <= 0;
elsif rising_edge(clk270) then
 
   clk27_d <= clk_27; -- for word boundary detection
 
   if clk27 = '1' and clk27_d = '0' then
      count <= 1;
   elsif count = 9 then
      count <= 0;
   else
      count <= count + 1;
   end if;
 
   q(count) <= data_in;
 
end if;
end process;