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Forum: FPGA, VHDL & Verilog Rectangular waveform generator in the range from 0 to 10MHz.


von Marek (Guest)


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To pass the subject had to do such a project: Rectangular waveform 
generator in the range from 0 to 10MHz. I have a all code, Behavioral 
simulation is good but post-fit is bed, becouse over time, an indefinite 
condition  'X' on a output.
What is wrong with this code? Please help

My code:
------------------------------------------------------------------------ 
----------
-- Company:
-- Engineer:
--
-- Create Date:    17:25:15 06/14/2014
-- Design Name:
-- Module Name:    Generator - Behavioral
-- Project Name:
-- Target Devices:
-- Tool versions:
-- Description:
--
-- Dependencies:
--
-- Revision:
-- Revision 0.01 - File Created
-- Additional Comments:
--
------------------------------------------------------------------------ 
----------
LIBRARY ieee;
use ieee.std_logic_1164.all;
--use IEEE.STD_LOGIC_ARITH.all;
--use ieee.std_logic_signed.all;
use ieee.std_logic_unsigned.all;
use ieee.numeric_std.all;


-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;



ENTITY Generator IS
PORT  (
      clk       : IN STD_LOGIC;      --100Mhz  (10ns)
    zadajnik1 : IN STD_LOGIC_VECTOR(3 downto 0);
    zadajnik2 : IN STD_LOGIC_VECTOR(3 downto 0);
    zadajnik3 : IN STD_LOGIC_VECTOR(3 downto 0);
    zadajnik4 : IN STD_LOGIC_VECTOR(3 downto 0);
    led1 : OUT STD_LOGIC;
    led2 : OUT STD_LOGIC;
      wyjscie   : OUT STD_LOGIC
    );

END Generator;

ARCHITECTURE Behavioral OF Generator IS

subtype shortint is integer range 0 to 1000000000;
subtype microint is integer range 0 to 9;

    signal nastaw1 : microint;
    signal nastaw2 : shortint;
    signal nastaw3 : microint;
    signal nastaw4 : shortint;

BEGIN

process (clk,zadajnik1,zadajnik2,zadajnik3,zadajnik4)

    variable count : std_logic_vector(29 downto 0) := (others => '0');
    variable count2 : std_logic_vector(29 downto 0) := (others => '0');
    variable count3 : std_logic_vector(3 downto 0) := (others => '0');
    variable count4 : std_logic_vector(3 downto 0) := (others => '0');

    begin

  if rising_edge(clk) then

  nastaw1 <= to_integer(unsigned(zadajnik1));
  nastaw3 <= to_integer(unsigned(zadajnik3));


      if (count = nastaw4) then
        count3 := count3 + 1;
        count := (others => '0');
        if (count3 <= nastaw3) then
          wyjscie <= '1';
        else
          wyjscie <= '0';
        end if;
      end if;
      if (count2 = nastaw2) then
        count4 := count4 + 1;
        count2 := (others => '0');
        if (count4 = nastaw1) then
          count3 := (others => '0');
          count4 := (others => '0');
        end if;
      end if;
      count := count + 1;
      count2 := count2 + 1;
  end if;


----------------------------------------------


if (nastaw2 > nastaw4) then
  led1 <= '0';
elsif (nastaw2 < nastaw4) then
  led1 <= '1';
elsif (nastaw2 = nastaw4) then
  if (nastaw1 > nastaw3) then
    led1 <= '0';
  else
    led1 <= '1';
  end if;
end if;


if ((nastaw1 = 0) or (nastaw3 = 0)) then
led2 <= '1';
else
led2 <= '0';
end if;



end process;



      with zadajnik2 select nastaw2 <=
              1 when "0000",
              10 when "0001", --10
              100 when "0010", --100
              1000 when "0011", --1 000
               10000 when "0100", --10 000
              100000 when "0101", --100 000
              1000000 when "0110", --1 000 000
              10000000 when "0111", --10 000 000
              100000000 when "1000", --100 000 000
              1000000000 when "1001", --1 000 000 000
              10 when others;


      with zadajnik4 select nastaw4 <=
              1 when "0000",
              10 when "0001", --10
              100 when "0010", --100
              1000 when "0011", --1 000
               10000 when "0100", --10 000
              100000 when "0101", --100 000
              1000000 when "0110", --1 000 000
              10000000 when "0111", --10 000 000
              100000000 when "1000", --100 000 000
              1000000000 when "1001", --1 000 000 000
              10 when others;

end Behavioral;

von Hans (Guest)


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Marek wrote:
> I have a all code, Behavioral
> simulation is good
Fine. So it shold work on your FPGA too.

> but post-fit is bed, becouse over time, an indefinite
> condition  'X' on a output.
There is an effect, called 'X'-propagation. You can search the reason 
for the 'X'.
Normaly a beahvioral simulation is enough. Post-fit timinig simulation 
is today only used in dodgy designs.
The statical timing analysis with proper clock constraint will help even 
more than a timing simulation.

> What is wrong with this code?
I would change some parts:

Marek wrote:
> LIBRARY ieee;
> use ieee.std_logic_1164.all;
> --use IEEE.STD_LOGIC_ARITH.all;
> --use ieee.std_logic_signed.all;
> use ieee.std_logic_unsigned.all;
> use ieee.numeric_std.all;
1. To make calculation use only numeric_std. Forget 
std_logic_unsigned, std_logic_signed and std_logic_arith. They are 
vendor specific and unstandardised (and wrong compiled to library ieee).


> variable count : std_logic_vector(29 downto 0) := (others => '0');
>     variable count2 : std_logic_vector(29 downto 0) := (others => '0');
>     variable count3 : std_logic_vector(3 downto 0) := (others => '0');
>     variable count4 : std_logic_vector(3 downto 0) := (others => '0');
2. As beginner avoid variables. Learn the specific behaviour of signals 
(latency), after that you can use variables.

3. Use the type unsigned for counters. std_logic_vectors are just a pile 
of bits. To make calculations (like the addition of 1) use unsigned. 
unsigned can easy compared with integer and can easy converted to slv, 
if needed.

regards,
Hans

von inzynier polski (Guest)


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Marek wrote:
> with zadajnik4 select nastaw4 <=
osobliwie sformulowanie :-)

Why do you transform the inpus to deicmal?
You should use binary increasing Counters to directly compare to the 
Input Parameters.

- dziwny zadanie ...

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