parse error: unexpected if in xilinx ise 8.1i

architecture Behavioral of addsubmain is

signal sL,sS :std_logic;
signal eL,eS:std_logic_vector(7 downto 0);
signal fracL,fracS:std_logic_vector(23 downto 0);

signal sX_B : std_logic;
signal op_X : std_logic;

signal diff : integer;

signal X_A : std_logic_vector(24+diff downto 0);
signal X_B : std_logic_vector(24+diff downto 0);
signal X_R : std_logic_vector(24+diff downto 0);

begin
sX_B <= oper xor s_B;

if exp_A < exp_B then
eS <= exp_A;
fracS <= frac_A;
sS <= s_A;
eL <= exp_B;
fracL <= frac_B;
sL <= sX_B;
elsif exp_B < exp_A then
eS <= exp_B;
fracS <= frac_B;
sS <= sX_B;
eL <= exp_A;
fracL <= frac_A;
sL <= s_A;
end if;
my code goes like this.. exp_A and exp_B have been declared as
std_logic_vectors of same size in the entity.
the xilinx ise tool shows "parse error: unexpected if" at the beginning of
this part of code, then "parse error: unexpected else" and also "error:
unexpected if, semicolon expected" at the line of end if.
i can't proceed without getting this conditional statement corrected. i
even tried using case instead of if.. but tat too is erroneous...

wat is wrong with my code?

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revu

revu wrote:

> architecture Behavioral of addsubmain is
>
> signal sL,sS :std_logic;
> signal eL,eS:std_logic_vector(7 downto 0);
> signal fracL,fracS:std_logic_vector(23 downto 0);
>
> signal sX_B : std_logic;
> signal op_X : std_logic;
>
> signal diff : integer;
>
> signal X_A : std_logic_vector(24+diff downto 0);
> signal X_B : std_logic_vector(24+diff downto 0);
> signal X_R : std_logic_vector(24+diff downto 0);
>
> begin
> sX_B <= oper xor s_B;
>
> if exp_A < exp_B then
> eS <= exp_A;
> fracS <= frac_A;
> sS <= s_A;
> eL <= exp_B;
> fracL <= frac_B;
> sL <= sX_B;
> elsif exp_B < exp_A then
> eS <= exp_B;
> fracS <= frac_B;
> sS <= sX_B;
> eL <= exp_A;
> fracL <= frac_A;
> sL <= s_A;
> end if;
> my code goes like this.. exp_A and exp_B have been declared as
> std_logic_vectors of same size in the entity.
> the xilinx ise tool shows "parse error: unexpected if" at the beginning of
> this part of code, then "parse error: unexpected else" and also "error:
> unexpected if, semicolon expected" at the line of end if.
> i can't proceed without getting this conditional statement corrected. i
> even tried using case instead of if.. but tat too is erroneous...
>
> wat is wrong with my code?

You can't use 'if' as a concurrent statement (i.e. outside a process). 'if'
is a sequential statement, so it can only be used in sequential areas, such
as processes, procedures and functions.

So I would suggest putting your stuff in a process.

Also, your signals are not assigned unconditionally, so you will create
latches. Add an else, or assign default values before the if.

ab_cmb: process(exp_A, exp_B, frac_A, frac_B, s_A, sX_B, exp_B) is
begin
if exp_A < exp_B then
eS <= exp_A;
fracS <= frac_A;
sS <= s_A;
eL <= exp_B;
fracL <= frac_B;
sL <= sX_B;
elsif exp_B < exp_A then
eS <= exp_B;
fracS <= frac_B;
sS <= sX_B;
eL <= exp_A;
fracL <= frac_A;
sL <= s_A;
else -- exp_A equals exp_B
eS <= ...;
fracS <= ...;
sS <= ...;
eL <= ...;
fracL <= ...;
sL <= ...;
end if;
end process ab_cmb;

--
Paul Uiterlinden
www.aimvalley.nl
e-mail addres: remove the not.

Paul Uiterlinden

revu wrote:
> architecture Behavioral of addsubmain is
....

> signal diff : integer;
>
> signal X_A : std_logic_vector(24+diff downto 0);
....
Is the above legal? You seem to have the width of X_A depend on the
value of diff? For that to work, diff would need to be a constant
(possibly a generic)?

David R Brooks

so is it legal if i declare the signal X_A after calculating diff ie, after
'begin' of the architecture??

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revu

revu wrote:

> so is it legal if i declare the signal X_A after calculating diff ie,
> after 'begin' of the architecture??

No, because after the 'begin' of an architecture you cannot declare signals.

The width of a signal is static (cannot change during simulation). So in the
declaration of a signal, its width can only be derived from constants and
generics. Not from the value of another signal or variable.

--
Paul Uiterlinden
www.aimvalley.nl
e-mail addres: remove the not.

Paul Uiterlinden

thanks paul.
as u said, when i put it inside a process, the code worked..

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revu