user defined functions in VHDL

Hi!

My problem is I have wrote a function with 3 input parameters (integer, integer and std_logic_vector) and return std_logic_vector. This package is synthesible. that OK

but in my VHDL code when I use the function it doesn't work.

the syntax is

SO <= fun 3 6 "101";

the error is

IN mode Formal xfrom of fun with no default value must be associated with an actual value.


any idea how to solve my problem?

bart

Bartart said:

Hi!
but in my VHDL code when I use the function it doesn't work.

the syntax is

SO <= fun 3 6 "101";

the error is

IN mode Formal xfrom of fun with no default value must be associated with an actual value.
bart

Click to expand...

I guess the parentheses were lost and you really meant:

SO <= fun(3,6,"101");

Can you post the definition of the function?

function fun(a:integer; b:integer; c:std_logic_vector) return std_logic_vector; ?

The error shows that there is at least one missing parameter.

This function gets two arguments as integer and a number as std_logic_vector. Output of the function is logic_vector with extended sign bit (MSB) of the input data.

example:

fun(3,6,"101") should return 111101
fun(8,6,"001") - || - 001 error

This is a function definition:

function fun (
signal xfrom : integer;
signalal xto : integer;
signal xdat : std_logic_vector ) return std_logic_vector is

variable lxdat : std_logic_vector ((xto - xfrom) downto 0 );

begin
if ((xto - xfrom) = 0 or (xto - xfrom) < 0 ) then
return xdat;
elsif (xto - xfrom) > 0 then
for i in xfrom to xto loop
lxdat(i + xfrom) := xdat(xfrom);
end loop;
return lxdat;
end if;
end fun;


I have tried with fun() but no effect.



thx vomit!

Bart

The problem here is the matching between actual and formal parameters:

you defined xfrom, xto and xdata (formal parameters) as signals, while the actual parameters you're using are constants.

You can:

1) define three signals A, B as integer, C as std_logic_vector and use them to pass actual parameters to the function;

2) remove the signal definition from formal parameters

Try to change you function definition as:

function fun ( xfrom : integer;
xto : integer;
xdat : std_logic_vector )
return std_logic_vector

It works fine!

Pay attention also to your implementation; imho there is some errors: if i've understood your intentions, the right code would be

function fun ( xfrom : integer;
xto : integer;
xdat : std_logic_vector )
return std_logic_vector is

variable lxdat : std_logic_vector ((xto - 1) downto 0 );

begin
if ((xto - xfrom) = 0 or (xto - xfrom) < 0 ) then
return xdat;
elsif (xto - xfrom) > 0 then
for i in 0 to xfrom - 1 loop
lxdat(i) := xdat(i);
end loop;
for i in xfrom - 1 to xto - 1 loop
lxdat(i) := xdat(xfrom-1);
end loop;
return lxdat;
end if;
end fun;

Hoping this will be an help for you,

Ro.