multiply two numbers

[Altera_Forum]

Hello. 

 I am a new to vhdl and as a part of my tranning i need to multiplay 2 numbers can u help me and tell my what i doing wrong?   LIBRARY IEEE; USE IEEE.STD_LOGIC_1164.ALL; use ieee.numeric_std.all;   ENTITY MUL IS PORT( a,b: IN unsigned (3 downto 0);    y : OUT unsigned (7 downto 0));  END MUL ; ARCHITECTURE Behavioral OF MUL IS  BEGIN  process (a,b)    variable temp1:unsigned(7 downto 0);  variable temp:unsigned(7 downto 0);    BEGIN      for j in 0 to 3 loop    if (b(j)='0') then   temp1:=(7 downto 0 =>'0');    else    temp1:=( j=>a(0),j+1=>a(1), j+2=>a(2),j+3=>a(3),others=>'0') ;    temp:=temp+temp1;     end if ;   end loop;   y<=temp;   end process;  END Behavioral;

[Altera_Forum]

whats wrong with  

 y <= a*b;  But if you need to build your own multuplier - you havent said what problems you are having with this code.

[Altera_Forum]

Yes i need to built my own multiplier my problem with the code is that logically i think it is ok and also compile but when i enter signals i am getting that y(out) is in unknown state.. 

 Thx.

[Altera_Forum]

That means temp is unknown and probably temp1 aswell 

Get a good testbench going in modelsim. This is debugging that you need to do yourself.

[Altera_Forum]

I am using a wrap program and active vhdl sim. so i dont need test banch can u see the code and maybe guide me why temp1 and temp getting an unknown state? 

Thx.

[Altera_Forum]

because temp is never initialised. 

And 'U' is not unknown, it is uninitialised. 'X' is unknown

[Altera_Forum]

Ok thx i will try to fix it thx.

[Altera_Forum]

I tried today this was not the issue but still thx .

[Altera_Forum]

--- Quote Start ---  I tried today this was not the issue but still thx .  --- Quote End ---   Are you referring to your original code? With Quartus synthesis, the missing initialization of temp is exactly the issue.