Problem converting to integer

Hi,

Read function description:

function TO_UNSIGNED ( ARG,SIZE: NATURAL) return UNSIGNED;

-- Result subtype: UNSIGNED (SIZE-1 downto 0)

-- Result: Converts a non-negative INTEGER to an UNSIGNED vector with

-- the specified SIZE.

As you can see you did not specify "SIZE" parameter and your REG_ADDR_IN has to be integer type also.

I recomend googling about libraries and packages usage in VHDL. I usualy use just two libraries:

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

and if you need some type conversion use:

https://www.doulos.com/knowhow/vhdl_designers_guide/numeric_std/ (https://www.doulos.com/knowhow/vhdl_designers_guide/numeric_std/)