Hi Willem,
> "Willem Oosthuizen" <> wrote in message
> news:begood$1u5$...
> > How do I do multi-dimentional arrays in components using generics
> >
> > I tried the following. This does not work. I need to define the type
> > array(Depth -1 downto 0) of std_logic_vector(Width-1 downto 0) and
> > type array(Depth -2 downto 0) of std_logic_vector(Width-2 downto 0)
> > somewhere. But where?
[and then...]
> I can put the types in a PACKAGE, but how do I pass the generics to the
> PACKAGE?
This is all a bit horrible in VHDL. When you make an array of something,
the full details of that "something" must be known. Your need for a
parameterisable 2-dimensional array is usually solved in one of the
following ways:
(1) Use a true 2-dimensional array
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
type Arr2D is array (Depth-1 downto 0, Width-1 downto 0) of std_logic;
This is legal VHDL, and you can then create arrays and subscript them:
signal S: Arr2D;
....
S(3,4) <= '0';
But unfortunately it doesn't play well with std_logic_vector
because there is no easy way to copy a row or column of this 2-d
array to/from a 1-D vector - you have to use a FOR loop.
(2) Put the subtype in a package
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
as you suggested...
package MyTypes is
constant Width: integer; --- deferred constant, no value
subtype Row_T is std_logic_vector(Width-1 downto 0);
end;
....
type Vec2D is array(Depth-1 downto 0) of Row_T;
But then, as you say, you need "to pass a generic
into the package". You can't do that. There is only
one "instance" of a package in any given VHDL simulation,
so the package can't have a generic. I've got close to
what you need by using a deferred constant; you set
up the deferred constant's value in the package body:
package body MyTypes is
constant Width: integer := 5;
end;
This package body can be compiled separately, just before
you elaborate the design, but the same Width value will apply
throughout the simulation.
(3) Fake it up with a big 1-D array
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
No help at all, because you can't take a slice
that has non-static bounds.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sorry I can't help more. It's a somewhat messy problem.
|
Similar Threads
