converting an array to a vector in VHDL

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shaiko

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Hi,

Suppose we have a VHDL array of 'n' elements and width of each element is 'k'.
How can we convert the array to a vector?

If we know the width and number of elements - we can use the concatenation operator:
-----------------------------------------------------------------------
type matrix is array (0 to 2) of std_logic_vector(7 downto 0);
signal concatenated_matrix: std_logic_vector(23 downto 0);

concatenated_matrix <= matrix(0) & matrix(1) & matrix(2);
-----------------------------------------------------------------------

But what if we want to write genericly ('k' and 'n' will be generics)
How can we code it?
 

May be write a function with for loop. Something like this.

for i in 0 to n loop
concatenated_matrix(k*i+k-1) <= matrix(i);
end loop;
 
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    shaiko

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you would need a function. (or wait until VHDL gets union types).

recall that my_array'range will return 0,1,2,...,N-1
recall that my_array(my_array'low)'range will return K-1,...,2,1,0
and the output is of size (my_array'length*my_array(my_array'low)'length-1 downto 0).

however, VHDL requires the function's input types be known. as a result, a single function cannot be used for any width/depth combo -- if you have 8b and 9b arrays, you'd a version of the function for each one, even through the code could otherwise be the same...
 
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    shaiko

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So...this type of code cannot be written genericly in VHDL?

---------- Post added at 13:42 ---------- Previous post was at 12:43 ----------

what about the following code (not in a function). given that "depth" and "width" are entity generics:

concatenating: for i in 0 to depth generate
concatenated_matrix((width - 1 + (i * width)) downto (i * width)) <= matrix(i);
end generate;

Will the above synthesize to a concatenated vector of all the array elements?
 

If I don't misunderstand the problem, it should work similar to vinipal's suggestion.

Code: 
for i in 0 to n loop
  concatenated_matrix(k*i+k-1 downto k*i) <= matrix(i);
end loop;

P.S.: I see, you found the solution yourself.
 
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    shaiko

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FvM, thanks for noting my mistake. I forgot the "downto" part..
 

Will the above synthesize to a concatenated vector of all the array elements?
Click to expand...

Yes it'll be fine, but it might be easier and neater to wrap it up in a function rather than a generate.

output <= concat_matrix( input );
 
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    shaiko

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