Array rotate : "Range bound must be a constant" in synthesis

Hello

I have one error message "Range bound must be a constant" duriung
synthesis.


I intend to rotate a variable sized integer array.
Array looks like {size, element,..,element }.
Number of elements = size.
I wish to get new array, rotated by "pos" value.


For example,
old array = { 4, 2, 3, 1, 4} and pos = 2
new array = { 4, 3, 1, 4, 2}.


Another example,
old array = { 5, 4, 2, 1, 3, 5 } and pos = 3
new array = { 5, 1, 3, 5, 4, 2 }


In order to implement that, I used "function", as shown in the
following.


1. I considered record type "parameters"


---- parameter to pass
type para is array (0 to size) of integer range 0 to size;
type parameters is record
old : para; -- old array
pos : integer range 0 to size; -- pos
end record;


2. I wrote a function below.


The code is not synthesizable.
Does anyone have idea how to make this synthesizable?
Thankyou.


-- generate new array from old array
function NEW_ARRAY( Temp: parameters ) return para is
variable array_out : para; -- new array
variable CTRL : integer range 0 to size; -- pos
variable IDX : integer range 0 to size; -- size
begin


CTRL := Temp.pos ;
IDX := Temp.old(0);


array_out(0) := Temp.old(0);


if ( IDX = 0 or CTRL = 0 ) then array_out := (others => 0 );
else


for I in CTRL to IDX loop
array_out(I - CTRL + 1) := Temp.old(I); ---- problematic
end loop;


for I in 1 to CTRL-1 loop
array_out(I + IDX - CTRL + 1) := Temp.old(I); ---- problematic
end loop;


end if;
return array_out;
end NEW_ARRAY;

Pasacco

Pasacco wrote:

> I have one error message "Range bound must be a constant" duriung
> synthesis.
....
> 2. I wrote a function below.
....
> The code is not synthesizable.
> Does anyone have idea how to make this synthesizable?

Synthesis infers logic between
entity input and output ports only.

Functions may be used to describe values,
which indirectly infer hardware, but
an entity and architecture are also
needed to describe assignments
to the output ports.

See how the functions
rising_edge and bit_done
are used in the reference design here:

http://home.comcast.net/~mike_treseler/


-- Mike Treseler

Mike Treseler