Indexing arrays in VHDL

Question

I have an array:

type offsets_type is array (4 downto 0) of std_logic_vector (4 downto 0); 
signal av     : offsets_type;

I want to do this, essentially: av[addr] += 1;
But this line:

 av(to_integer(unsigned(addr))) <= unsigned(av(to_integer(unsigned(addr))) + 1;

yields this error:
to_integer can not have such operands in this context.

I've also tried using conv_integer, but that gives Wrong type of index as an error.

Any solutions? Thanks.

Answer 1

There are a few problems in your code:

1. You cast the result of your calculation to an unsigned, while the left-hand side is std_logic_vector
2. There might be something wrong with the data type of addr, but you have not shared that with us.
3. There is a closing parenthese missing in the assignment.

It will be easier if you use "unsigned" in your type definitions. This way, you express that the bit pattern is actually something you want to use in integer arithmetic.

type offsets_type is array (4 downto 0) of unsigned (4 downto 0);
signal av     : offsets_type;
signal addr :unsigned(2 downto 0);

This will save you a few type conversions:

av(to_integer(addr)) <= av(to_integer(addr)) + "1";

Edit: you did use ieee.numeric_std.all didn't you?