This is my main code in VHDL:
library ieee;
USE ieee.std_logic_1164.all;
use ieee.numeric_std.all;
entity pid is
port( error ,Kp, Ti, Td ,dt: in std_logic_vector(7 downto 0);
reset : in std_logic;
output :out std_logic_vector(31 downto 0) );
end pid;
architecture pid_arch of pid is
-------------------------------- functions
function add_vec(num1,num2,num3: in std_logic_vector(15 downto 0)) return std_logic_vector is
variable v_TEST_VARIABLE1: integer;
variable v_TEST_VARIABLE2: integer;
variable v_TEST_VARIABLE3: integer;
variable n_times1: integer;
variable n_times2: integer;
variable sum: integer;
begin
v_TEST_VARIABLE1 := to_integer(unsigned(num1)) ;
v_TEST_VARIABLE2 := to_integer(unsigned(num2)) ;
v_TEST_VARIABLE3 := to_integer(unsigned(num3 ));
--for n_times1 in 1 to v_TEST_VARIABLE2 loop
-- v_TEST_VARIABLE1: = v_TEST_VARIABLE1 + '1';
-- end loop;
-- for n_times2 in 1 to v_TEST_VARIABLE3 loop
-- v_TEST_VARIABLE1:= v_TEST_VARIABLE1 + '1';
-- end loop;
sum:= v_TEST_VARIABLE1+ v_TEST_VARIABLE2 + v_TEST_VARIABLE3;
return std_logic_vector(to_unsigned(sum,32));
end add_vec;
-----------------------------------
function sub(num1, num2: in std_logic_vector(7 downto 0)) return std_logic_vector is
variable v_TEST_VARIABLE1: integer;
variable v_TEST_VARIABLE2: integer;
variable difference: integer;
begin
v_TEST_VARIABLE1 := to_integer(unsigned(num1)) ;
v_TEST_VARIABLE2 := to_integer(unsigned(num2)) ;
difference := v_TEST_VARIABLE1 - v_TEST_VARIABLE2;
return std_logic_vector(to_unsigned(difference,8));
end sub;
------------------------------------
function mul(num1,num2 : in std_logic_vector(7 DOWNTO 0)) return std_logic_vector is
variable v_TEST_VARIABLE1 : integer;
variable v_TEST_VARIABLE2 : integer;
variable n_times: integer:=1;
variable product: integer:=0;
begin
v_TEST_VARIABLE1 := to_integer(unsigned(num1)) ;
v_TEST_VARIABLE2 := to_integer(unsigned(num2)) ;
for n_times in 1 to v_TEST_VARIABLE2 loop
product:=product + v_TEST_VARIABLE1;
end loop;
return std_logic_vector(to_unsigned(product,16));
end mul;
--------------------------------
function div(num1, num2 : in std_logic_vector(7 DOWNTO 0)) return std_logic_vector is
variable v_TEST_VARIABLE1 : integer;
variable v_TEST_VARIABLE2 : integer;
variable quotient :integer;
-- begin
--P3: PROCESS(num1, num2)
variable n_times: integer:=1;
begin
if num1>num2 then
v_TEST_VARIABLE1 := to_integer(unsigned(num1)) ;
v_TEST_VARIABLE2 := to_integer(unsigned(num2)) ;
L1:loop
n_times := n_times + 1;
exit when ((v_TEST_VARIABLE2 - v_TEST_VARIABLE1)>0);
v_TEST_VARIABLE1 := v_TEST_VARIABLE1 - v_TEST_VARIABLE2;
end loop L1;
quotient := n_times-1;
elsif num2>num1 then
v_TEST_VARIABLE1 := to_integer(unsigned(num1)) ;
v_TEST_VARIABLE2 := to_integer(unsigned(num2)) ;
L2:loop
n_times:=n_times+1;
exit when ((v_TEST_VARIABLE1 - v_TEST_VARIABLE2)>0);
v_TEST_VARIABLE2 := v_TEST_VARIABLE2 - v_TEST_VARIABLE1;
quotient := n_times-1;
end loop L2;
else
quotient := 1;
end if;
return std_logic_vector(to_unsigned(quotient,16));
-- end PROCESS P3;
end div;
---------------------------------
function derivative(error, previous_error, dt :in std_logic_vector(7 downto 0)) return std_logic_vector is
variable derivative_val: std_logic_vector(15 downto 0);
begin
derivative_val := div(sub(error,previous_error),dt);
return derivative_val;
end derivative;
--------------------------------------------
function integration(error,dt:in std_logic_vector(7 downto 0);current_integration :in std_logic_vector(15 downto 0);reset : in std_logic) return std_logic_vector is
begin
if (reset='1') then
return "0000000000000000";
else
--current_integration := add_vec(current_integration, mul(error,dt),x"0000");
-- return current_integration;
return add_vec(current_integration, mul(error,dt),x"0000");
end if;
end integration;
-------------------------
begin
P1:PROCESS (reset ,error , Kp, Ti, Td)
variable proportional_term : std_logic_vector(15 downto 0):=x"0000";
variable derivative1: std_logic_vector(15 downto 0) := x"0000";
variable derivative_term: std_logic_vector(31 downto 0) ;
variable integration1: std_logic_vector(15 downto 0) :=x"0000";
variable integration_term : std_logic_vector(15 downto 0) := x"0000";
variable current_integration: std_logic_vector(15 downto 0) ;
variable previous_error: std_logic_vector(7 downto 0) := "00000000";
variable v1: std_logic_vector( 15 downto 0);
variable v2 : std_logic_vector( 23 downto 0);
variable v3 : std_logic_vector (7 downto 0);
------------------checked till here
begin
if (reset='1') then
-- output <= x"00000000";
previous_error :="00000000";
current_integration := x"0000";
else
--output <= Kp*(error + integration/Ti + derivative*Td);
current_integration := integration1;
end if;
-- proportional_term := mul(Kp,error);
proportional_term := std_logic_vector(unsigned(Kp) * unsigned(error));
-- derivative_term := mul(mul(Kp,Td), derivative(error, previous_error,dt));
v1 :=std_logic_vector(unsigned(Kp)*unsigned(Td));
derivative1 := derivative(error, previous_error,dt);
derivative_term := std_logic_vector(unsigned(v1)*unsigned(derivative1));
integration1 :=integration(error,dt,current_integration,reset);
v2 :=std_logic_vector((unsigned(Kp)*unsigned(integration1)));
v3 := std_logic_vector(resize(unsigned(v2),8));
integration_term := div( v3, Ti);
-- integration_term := div(mul(Kp, integration(error,dt,current_integration,reset)) , Ti);
previous_error :=error;
output <= add_vec(std_logic_vector(resize(unsigned(proportional_term),16)) , std_logic_vector(resize(unsigned(derivative_term),16)), std_logic_vector(resize(unsigned(integration_term),16)));
--output <= x"0000";
--Kp*(error + integration/Ti + derivative*Td);
END PROCESS P1;
end pid_arch;
And this is the testbench:
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
use IEEE.numeric_std.all;
ENTITY pid_2_tb IS
END pid_2_tb;
ARCHITECTURE behavior OF pid_2_tb IS
COMPONENT pid --'test' is the name of the module needed to be tested.
port(error ,Kp, Ti, Td ,dt: in std_logic_vector(7 downto 0);
reset : in std_logic;
output :out std_logic_vector(31 downto 0) );
END COMPONENT;
signal error : std_logic_vector(7 downto 0) := "00000000";
signal Kp : std_logic_vector(7 downto 0) := "00001000";
signal Ti : std_logic_vector(7 downto 0) := "00000001";
signal Td : std_logic_vector(7 downto 0) := "00000001";
signal dt : std_logic_vector(7 downto 0) := "00000001";
signal reset : std_logic := '1';
signal output : std_logic_vector(31 downto 0);
constant clk_period : time := 1 ns;
BEGIN
uut: pid PORT MAP (
error => error,
Kp => Kp,
Ti => Ti,
Td => Td,
dt => dt,
reset => reset,
output => output
);
clk_process :process
begin
error <= "00000001";
reset <= '1';
wait for clk_period/2;
error <= "00000010";
reset <= '0';
wait for clk_period/2; --for next 0.5 ns signal is '1'.
end process;
-- Stimulus process
stim_proc: process
begin
wait for 17 ns;
error <= "00000011";
reset <= '0';
wait for 1 ns;
error <= "00000010";
reset <= '0';
wait;
end process;
END;
The two show no error on compilation. I have tried simulating for smaller programs using the same functions, and that worked well. But on simulation it gives Fatal error. What can be the reasons for the same? I am a newbie in vhdl. Please help me out. Thanks in advance.
The div function uses a loop where the exit condition never becomes true,
whereby the div function will never return, thus the simulation time will
never advance.
One relevant part of the div code is in:
elsif num2 > num1 then
v_TEST_VARIABLE1 := to_integer(unsigned(num1));
v_TEST_VARIABLE2 := to_integer(unsigned(num2));
L2 : loop
n_times := n_times+1;
exit when ((v_TEST_VARIABLE1 - v_TEST_VARIABLE2) > 0);
v_TEST_VARIABLE2 := v_TEST_VARIABLE2 - v_TEST_VARIABLE1;
quotient := n_times-1;
end loop L2;
But if num1 is 0 (zero) then v_TEST_VARIABLE2 is never decremented in the
loop, thus ((v_TEST_VARIABLE1 - v_TEST_VARIABLE2) > 0) never becomes true.
The div function must be updated to handle this case also, or arguments must
be guaranteed never to result in the case.