Hi all, i'm trying to design a floating point adder using advantage pro and i simulating it using modelsim attached my code

LIBRARY ieee; USE ieee.std_logic_1164.all; USE ieee.std_logic_arith.all; ENTITY fp_adder IS -- Declarations port(a,b: in std_logic_vector(31 downto 0); c: out std_logic_vector(31 downto 0) ); END fp_adder ; -- hds interface_end ARCHITECTURE adder OF fp_adder IS --declaration of sign signal sa,sb,sc: std_logic; --declaration of exponent signal tea,teb: std_logic_vector(7 downto 0); signal ea,eb,ec: unsigned(7 downto 0); --declaration of mantissa signal tma,tmb: std_logic_vector(22 downto 0); signal ma,mb,mc: unsigned(22 downto 0); BEGIN --asignement of sign signals sa <= a(31); sb <= b(31); --assignement of exponent signals tea <= std_logic_vector(a(30 downto 23)); teb <= std_logic_vector(b(30 downto 23)); ea <= unsigned(tea); eb <= unsigned(teb); --assignement of mantissa signals tma <= std_logic_vector(a(22 downto 0)); tmb <= std_logic_vector(b(22 downto 0)); ma <= unsigned(tma); mb <= unsigned(tmb); ------------------------------------------------------------------------------------------------------ process(ea,eb,ec,ma,mb,mc,sa,sb,sc) begin if(ea > eb)then loop eb <= eb+1; mb <= '0'& mb(22 downto 1); exit when ea=eb; end loop; mc <= ma+mb; ec <= ea; sc <= sa xor sb; elsif(eb > ea) then loop ea <= ea+1; ma <= '0'& ma(22 downto 1); exit when ea=eb; end loop; mc <= ma+mb; ec <= ea; sc <= sa xor sb; else mc <= ma+mb; ec <= ea; sc <= sa xor sb; end if; end process; c(22 downto 0) <= std_logic_vector(mc); c(30 downto 23) <= std_logic_vector(ec); c(31) <= sc; END adder; |

and i found a problem which i couldn't recognize it there is no error in compiling the code but at simulation the o/p is UUUUUUUUUUUUUUUUUUUU

and there is some warnings at modelsim command window this is the error massage # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 0 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 0 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 0 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 0 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 0 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 0 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 1 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 1 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 1 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 1 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 1 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 1 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 2 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 2 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 2 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 2 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 2 Instance: /fp_adder # ** Warning: There is an 'U'|'X'|'W'|'Z'|'-' in an arithmetic operand, the result will be 'X'(es). # Time: 0 ns Iteration: 2 Instance: /fp_adder |

could anyone help me to solve this error is my design synthesizable?

```
> could anyone help me to solve this error
This is no error, it is a warning ;-)
Try default values for your signals:
```

signal tea,teb: std_logic_vector(7 downto 0) := (others=>'0'); signal ea,eb,ec: unsigned(7 downto 0) := (others=>'0'); |

```
> is my design synthesizable?
```

if(ea > eb)then loop |

No. Loops like this are not synthesisable.

thanks alot i do what you suggest it works right when i add 0+0 but the o/p xxxxxxxxxxxx sorry but could you advice me how to test it

this the new vhdl code after add a default value for all internal signals

LIBRARY ieee; USE ieee.std_logic_1164.all; USE ieee.std_logic_arith.all; ENTITY fp_adder IS -- Declarations port(a,b: in std_logic_vector(31 downto 0); c: out std_logic_vector(31 downto 0) ); END fp_adder ; -- hds interface_end ARCHITECTURE adder OF fp_adder IS --declaration of sign signal sa,sb,sc: std_logic:= '0'; --declaration of exponent signal tea,teb: std_logic_vector(7 downto 0):= (others=>'0'); signal ea,eb,ec: unsigned(7 downto 0):= (others=>'0'); --declaration of mantissa signal tma,tmb: std_logic_vector(22 downto 0):= (others=>'0'); signal ma,mb,mc: unsigned(22 downto 0):= (others=>'0'); BEGIN --asignement of sign signals sa <= a(31); sb <= b(31); --assignement of exponent signals tea <= std_logic_vector(a(30 downto 23)); teb <= std_logic_vector(b(30 downto 23)); ea <= unsigned(tea); eb <= unsigned(teb); --assignement of mantissa signals tma <= std_logic_vector(a(22 downto 0)); tmb <= std_logic_vector(b(22 downto 0)); ma <= unsigned(tma); mb <= unsigned(tmb); ------------------------------------------------------------------------------------------------------ process(ea,eb,ec,ma,mb,mc,sa,sb,sc) begin if(ea > eb)then loop eb <= eb+1; mb <= '0'& mb(22 downto 1); exit when ea=eb; end loop; mc <= ma+mb; ec <= ea; sc <= sa xor sb; elsif(eb > ea) then loop ea <= ea+1; ma <= '0'& ma(22 downto 1); exit when ea=eb; end loop; mc <= ma+mb; ec <= ea; sc <= sa xor sb; else mc <= ma+mb; ec <= ea; sc <= sa xor sb; end if; end process; c(22 downto 0) <= std_logic_vector(mc); c(30 downto 23) <= std_logic_vector(ec); c(31) <= sc; END adder; |

i try to test my desig my put a =.25 "00000000101000000000000000000000" b =.25 "00000000101000000000000000000000" so sa=0 sb=0 sc=0 tea=000000001 teb=000000001 ea=0000000X --i can't understand why? eb=0000000X --i can't understand why? tma=01000000000000000000000 tmb=01000000000000000000000 ma=0X000000000000000000000 --i can't understand why? mb=0X000000000000000000000 --i can't understand why? mc=XXXXXXXXXXXXXXXXXXXXXXX but i expect to be ="10000000000000000000000" plz can you explain why there's unknown bits?

Try type conversion without temporary signals, like here:

--assignement of exponent signals ea <= unsigned(a(30 downto 23)); eb <= unsigned(b(30 downto 23)); --assignement of mantissa signals ma <= unsigned(a(22 downto 0)); mb <= unsigned(b(22 downto 0)); |

Duke P.S.: I suggest to use records:

type float_t is record s: std_logic; e: unsigned(7 downto 0); m: unsigned(22 downto 0); end record; |

You can use it like: c.m <= a.m + b.m;

There are some fundamental problems in your code. Is this supposed to be a clocked or combinatorial adder? Because at the moment it is neither. You have signals that are not assigned in every branch, signals that are assigned their previous values, loops with non-constant exit conditions - all that will blow up when you try to synthesize it. I suggest you follow the rules in http://embdev.net/articles/VHDL and look at some examples.

If you just need a FPAdder, try FloPoCo: http://www.ens-lyon.fr/LIP/Arenaire/Ware/FloPoCo/ It's VERY advanced, you can customize all parameters such as pipeline depth, mantissa width, internal representation, ... What you get is a perfectly synthesizable VHDL entity. Plus it's free!

@ Andreas Schwarz thanks for your help but sorry i'm new at vhdl could u explain to me what's record and how can i use it i'm trying to read about it from vhdl by example but i understand nothing. @ Ras Funk thanks alot for your post but i have to do it by myself coz i'll use it at my graduation project