Generic: use constant or not?

[Ricardo]

Hello,

The generic part of entity declaration. I've found that there are two
ways, like:

GENERIC ( constant value : integer := 5 )

or

GENERIC ( value : integer := 5 )

Both ways seem to work fine, for synthesis and simulation. I suppose
they are equivalent. Wich difference the "constant" do? Any comments?

Regards,

Ricardo.

 

[Mike Treseler]

Ricardo wrote:

The generic part of entity declaration. I've found that there are two
ways, like:
GENERIC ( constant value : integer := 5 )
or
GENERIC ( value : integer := 5 )

Both ways seem to work fine, for synthesis and simulation. I suppose
they are equivalent.

yes

Wich difference the "constant" do? Any comments?


I leave out the "constant" because
a generic cannot be of any other class.
If someday there are other options
(generic types would be nice!), I expect
that constant will still be the default class.

-- Mike Treseler

 

[Schüle Daniel]

Ricardo schrieb:

Hello,

The generic part of entity declaration. I've found that there are two
ways, like:

GENERIC ( constant value : integer := 5 )

or

GENERIC ( value : integer := 5 )

Both ways seem to work fine, for synthesis and simulation. I suppose
they are equivalent. Wich difference the "constant" do? Any comments?

from my book 'A VHDL primer'
"A generic declares constant object of mode -in-"

whether you write constant or not, it's constant per default
the same is true for procedures

procedure test(a: in bit, b: out bit);
if object class is omited then parameters with
-in- mode are implicitely constant and thoese with
-inout- or -out- mode are variable's and could be written as

procedure test(constant a: in bit, variable b: out bit);

if one wants b to be signal this should be then

procedure test(constant a: in bit, signal b: out bit);

hth, Daniel