Subversion Repositories light8080

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-- l80pkg.vhdl -- Support package for Light8080 SoC.

--

-- Contains functions used to initialize internal BRAM with object code.

--

-- This package will be used from the object code package where the program

-- initialized RAM constant is defined. If you use script obj2hdl it will 

-- take care of this for you.

-- The package is used in entity l80soc too, and nowhere else.

--

-- This file and all the light8080 project files are freeware (See COPYING.TXT)

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library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

package l80pkg is

-- Basic array type for the declaration of initialization constants.

-- This type is meant to be used to declare a constant with the object code

-- that is to be preprogrammed in an initialized RAM.

type obj_code_t is array(integer range <>) of std_logic_vector(7 downto 0);

-- Basic array type for the definition of initialized RAMs.

type ram_t is array(integer range <>) of std_logic_vector(7 downto 0);

-- Builds BRAM initialization constant from a constant CONSTRAINED byte array

-- containing the application object code.

-- The object code is placed at the beginning of the BRAM and the rest is

-- filled with zeros.

-- CAN BE USED IN SYNTHESIZABLE CODE to compute a BRAM initialization constant 

-- from a constant argument.

-- 

-- oC: Object code table (as generated by utility script obj2hdl for instance).

-- size: Size of the target memory.

-- Returns ram_t value size-bytes long, suitable for synth-time initialization 

-- of a BRAM.

function objcode_to_bram(oC : obj_code_t; size : integer) return ram_t;

-- Compute log2(A), rounding up. 

-- Use this to get the minimum width of the address bus necessary to

-- address A locations.

function log2(A : natural) return natural;

end package;

package body l80pkg is

-- Builds BRAM initialization constant from a constant CONSTRAINED byte array

-- containing the application object code.

function objcode_to_bram(oC : obj_code_t; size : integer) return ram_t is

variable br : ram_t(integer range 0 to size-1);

variable i : integer;

variable obj_size : integer;

begin

    -- If the object code table is longer than the array size, truncate code

    if oC'length > size then

        obj_size := size;

    else

        obj_size := oC'length;

    end if;

    -- Copy object code to start of BRAM...

    for i in 0 to obj_size-1 loop

        br(i) := oC(i);

    end loop;

    -- ... and fill the rest with zeros

    br(obj_size to size-1) := (others => x"00");

    return br;

end function objcode_to_bram;

function log2(A : natural) return natural is

begin

    for I in 1 to 30 loop -- Works for up to 32 bit integers

        if(2**I >= A) then

            return(I);

        end if;

    end loop;

    return(30);

end function log2;

end package body;