[SOLVED] VHDL LOOP IS NOT WORKING

[Soh_bhat]

Hi there,
I have tried to add and subtract to check the for loop using two equations. But, whenever I am using it, it is giving result of first step only and the loop is unrolling. What is the error in my code?

Behavioural:
package pk5 is
 type T is range 0.0 to 50.0;
 type T1 is array (0 to 3) of T;
end pk5;

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;
use work.pk5.all;

entity add is
   Port ( x : in T1 ;
          y : in T1;
          h : in T;
          x_o : out T1;
          y_o : out T1);
end add;

architecture Behavioral of add is

signal p, q : T1;

begin

process(x, y, h)
begin
x_o(0) <= 0.0;
y_o(0) <= 0.0;

addi: for i in 1 to 3 loop
x_o(i) <= x(i-1) + h;
y_o(i) <= y(i-1) - x(i-1);
end loop;

end Behavioural;

Test Bench:
library IEEE;

use IEEE.STD_LOGIC_1164.ALL;
use work.pk5.all;

entity add_TB is

end add_TB;

architecture Behavioral of add_TB is

component add is
Port ( x : in T1;
          y : in T1;
          h : in T;
          x_o : out T1;
          y_o : out T1);
end component;

signal x: T1;
signal y: T1;
signal h: T;
signal x_o: T1;
signal y_o: T1;

begin

uut: add port map (
x => x,
y => y,
h => h,
x_o => x_o,
y_o => y_o);

add_proc: process
begin
 x(0) <= 1.0;
   y(0) <= 10.0;
   h <= 0.1;
  wait for 5 ns;
 end process;

 end Behavioral;

It is giving the first output only.

PLease help!!!

 

[FvM]

The error is in the assumption that the left-hand side of signal assignments would be instantly updated. This is not the case, the signals are updated at process exit. If you want to use the result of a previous assignment in the process flow, you have to refer to variables.

--- Updated Sep 1, 2022 ---

Consider also that the real subtype "range 0.0 to 50.0" isn't synthesizable, but it can be used in a simulation.

 

[Soh_bhat]

So, I have to use variable inside the loop and define the output outside the loop.That's what you are saying?
Could you please share a short syntax regarding this, then that would be pretty much helpful for me.Your time and consideration is really appreciated.

 

[Soh_bhat]

I I do this,
begin

process(x, y, h)
 variable p, q : T1;
begin
--x_o(0) <= 0.0;
--y_o(0) <= 0.0;

addi: for i in 1 to 3 loop
p(i) := x(i-1) + h;
q(i) := y(i-1) - x(i-1);
end loop;

x_o(3) <= p(3);
y_o(3) <= q(3);

end process;

Answer is not coming. Only the input value is showing, output shows as 0.
Please help.

 

[FvM]

You want to do something like this

p(0) := x(0);
q(0) := y(0);
for i in 1 to 3 loop
   p(i) := p(i-1) + h;
   q(i) := q(i-1) - x(i-1);
end loop;

 

[Soh_bhat]

Thanks a lot. It's running. Thanks a ton for the help.