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;