IEEE 200X Fast Track Change Proposal

ID:	  FT-14

Proposer:     Jim Lewis 
email:        Jim@SynthWorks.com

Status:       Proposed
Proposed:     12/03
Analyzed:     Date
Resolved:     Date

Enhancement Summary:     Arrays of unconstrained arrays
Related issues:          FT-14
Relevant LRM section:    

Enhancement Detail:
----------------------------
type std_logic_matrix is array (natural range<>) of std_logic_vector;
type std_logic_matrix2 is array (natural range<>, natural range<>)
            of std_logic_vector ; 

subtype Matrix_5x5 is std_logic_matrix(4 downto 0)(4 downto 0) ;

signal A : std_logic_matrix(7 downto 0)(5 downto 0) ; 

-- Accessing a Row
A(5) <= "111000" ;
-- Accessing an Element
A(7)(5) <= '1' ;

entity e is
generic (
  width : integer := 2 ;
  depth : integer := 2 
) ;
port (
A : std_logic_matrix(7 downto 0)(5 downto 0) ;
B : std_logic_matrix(Depth -1 downto 0)(Width-1 downto 0);
. . .
) ;



-----------------------
COMPONENT Reduce is
generic
( Width : integer;
  Depth : integer
);
port
( D_IN  : IN  array(Depth -1 downto 0) of
              std_logic_vector(Width-1 downto 0);
  Q     : OUT array(Depth -2 downto 0) of
              std_logic_vector(Width-2 downto 0);
);
end COMPONENT; 

Form 1:  unconstrained array of unconstrained array
  type two_dim_arrayofarray is array(natural <>) of std_logic_vector ;

  signal A  : two_dim_arrayofarray (Depth-1 downto 0)(Width-1 downto 0) ;
  signal A2 : two_dim_arrayofarray (Depth-2 downto 0)(Width-2 downto 0) ;

  Currently arrays of arrays are really useful as one can manipulate
  a row as follows:

  signal D : std_logic_vector(Width-1 downto 0) ;

  D <= A(1) ;


  A further interesting extension would be to be able to grab a column
  as follows:

  signal G, H : std_logic_vector(Depth-1 downto 0) ;

  G <= A(Depth-1 downto 0)(1) ;
  H <= A(all)(1) ;

  Since one is really accessing a column of elements of std_logic,
  a type conversion may be required:

  G <= std_logic_vector(A(Depth-1 downto 0)(1)) ;
  H <= std_logic_vector(A(all)(1)) ;

  Perhaps further capability, but not justified by this example:
  A2 <= A(Width-2 downto 0)(Depth-2 downto 0) ;

------------------------------------
Form 3:  Two dimensional arrays
  type two_dim_array is array(natural <>, natural <>) of std_logic ;

  signal C  : two_dim_array(Depth-1 downto 0, Width-1 downto 0) ;
  signal C2 : two_dim_array(Depth-2 downto 0, Width-2 downto 0) ;

  Currently this one is not too interesting because one cannot access
  an entire row at a time, but if I could do the following this would
  be interesting:

  signal D, E, F : std_logic_vector(Width-1 downto 0) ;

  D <= C(1, Width-1 downto 0) ;
  E <= C(1, all) ; -- all = key word to replace the entire index of that object
  E <= C(1, *) ;   -- an alternate to all
  F <= C(1) ;  -- by default if a multidim object is referenced and only one
               -- index is specified it is the left most index
               -- this may be a bad thing for a strong typed language like VHDL

  OOPS, the above probably require type conversion/casting?
  D <= std_logic_vector(C(1, Width-1 downto 0)) ;
  E <= std_logic_vector(C(1, all)) ;
  . . .

  Even more interesting, a capability we don't have now:
  signal G : std_logic_vector(Depth-1 downto 0) ;

  G <= std_logic_vector(C(all, 2)) ; -- all elements from column 2

  Perhaps further capability, but not justified by this example:
  C2 <= C(Width-2 downto 0, Depth-2 downto 0) ;

Analysis:
----------------------------
[To be performed by the 200X Fast Track Working Group]


Resolution:
----------------------------
[To be performed by the 200X Fast Track Working Group]