Range constants?

[Tim Hubberstey]

It is often necessary to extract portions of a vector using a slice.
Whenever I do this, I use constants for maintainability. I have been
using what I refer to as "range constants" where I define a vector
constant that I don't intend to use directly and then use the 'range
attribute on it to define a slice:

--------
-- define a "range constant" in a package
constant SomeField : std_logic_vector(21 downto 15)
:= (others => 'X');
--------
out_vec <= source_vec(SomeField'range);
--------

While this works quite well, it seems somewhat messy. Is there a cleaner
way to do this?
--
Tim Hubberstey, P.Eng. . . . . . Hardware/Software Consulting Engineer
Marmot Engineering . . . . . . . VHDL, ASICs, FPGAs, embedded systems
Vancouver, BC, Canada . . . . . . . . . . . http://www.marmot-eng.com

 

[Mike Treseler]

Tim Hubberstey wrote:

constant SomeField : std_logic_vector(21 downto 15)
:= (others => 'X');
out_vec <= source_vec(SomeField'range);
While this works quite well, it seems somewhat messy. Is there a cleaner
way to do this?

That does the job.
I might declare and use
an array or record type to do the same thing.

-- Mike Treseler

 

[Jonathan Bromley]

On Fri, 25 Jun 2004 18:44:58 GMT, Tim Hubberstey <bogus@bogusname.com>
wrote:

[...]

-- define a "range constant" in a package
constant SomeField : std_logic_vector(21 downto 15)
:= (others => 'X');
--------
out_vec <= source_vec(SomeField'range);
--------

While this works quite well, it seems somewhat messy. Is there a cleaner
way to do this?

Subtypes?

subtype SomeFieldRange is natural range 21 downto 15;
-----------
out_vec <= source_vec(SomeFieldRange);

Make sure your subtype has the same direction (to/downto)
as the subscripts of source_vec.

Cheers
--
Jonathan Bromley, Consultant

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