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---------------------------------------------------------------------

-- TITLE: MIPS Misc. Package

-- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)

-- DATE CREATED: 2/15/01

-- FILENAME: mips_pack.vhd

-- PROJECT: MIPS CPU core

-- COPYRIGHT: Software placed into the public domain by the author.

--    Software 'as is' without warranty.  Author liable for nothing.

-- DESCRIPTION:

--    Data types, constants, and add functions needed for the MIPS CPU.

---------------------------------------------------------------------

library ieee;

use ieee.std_logic_1164.all;

package mips_pack is

   constant ZERO          : std_logic_vector(31 downto 0) :=

      "00000000000000000000000000000000";

   constant ONES          : std_logic_vector(31 downto 0) :=

      "11111111111111111111111111111111";

--   type alu_function_type is (alu_nothing, alu_add, alu_subtract, 

--      alu_less_than, alu_less_than_signed, alu_equal, alu_not_equal,

--      alu_ltz, alu_lez, alu_eqz, alu_nez, alu_gez, alu_gtz,

--      alu_or, alu_and, alu_xor, alu_nor);

   subtype alu_function_type is std_logic_vector(4 downto 0);

   constant alu_nothing   : alu_function_type := "00000";

   constant alu_add       : alu_function_type := "00010";

   constant alu_subtract  : alu_function_type := "00011";

   constant alu_less_than : alu_function_type := "00100";

   constant alu_less_than_signed : alu_function_type := "00101";

   constant alu_equal     : alu_function_type := "00110";

   constant alu_not_equal : alu_function_type := "00111";

   constant alu_ltz       : alu_function_type := "01000";

   constant alu_lez       : alu_function_type := "01001";

   constant alu_eqz       : alu_function_type := "01010";

   constant alu_nez       : alu_function_type := "01011";

   constant alu_gez       : alu_function_type := "01100";

   constant alu_gtz       : alu_function_type := "01101";

   constant alu_or        : alu_function_type := "01110";

   constant alu_and       : alu_function_type := "01111";

   constant alu_xor       : alu_function_type := "10001";

   constant alu_nor       : alu_function_type := "10010";

--   type shift_function_type is (

--      shift_nothing, shift_left_unsigned,

--      shift_right_signed, do_right_unsigned);

   subtype shift_function_type is std_logic_vector(1 downto 0);

   constant shift_nothing        : shift_function_type := "00";

   constant shift_left_unsigned  : shift_function_type := "01";

   constant shift_right_signed   : shift_function_type := "11";

   constant shift_right_unsigned : shift_function_type := "10";

--   type mult_function_type is (

--      mult_nothing, mult_read_lo, mult_read_hi, mult_write_lo, 

--      mult_write_hi, mult_mult, mult_divide, mult_signed_divide);

   subtype mult_function_type is std_logic_vector(2 downto 0);

   constant mult_nothing       : mult_function_type := "000";

   constant mult_read_lo       : mult_function_type := "001";

   constant mult_read_hi       : mult_function_type := "010";

   constant mult_write_lo      : mult_function_type := "011";

   constant mult_write_hi      : mult_function_type := "100";

   constant mult_mult          : mult_function_type := "101";

   constant mult_divide        : mult_function_type := "110";

   constant mult_signed_divide : mult_function_type := "111";

--   type a_source_type is (from_reg_source, from_imm10_6);

   subtype a_source_type is std_logic_vector(1 downto 0);

   constant a_from_reg_source : a_source_type := "00";

   constant a_from_imm10_6    : a_source_type := "01";

   constant a_from_pc         : a_source_type := "10";

--   type b_source_type is (from_reg_target, from_imm, from_signed_imm);

   subtype b_source_type is std_logic_vector(1 downto 0);

   constant b_from_reg_target : b_source_type := "00";

   constant b_from_imm        : b_source_type := "01";

   constant b_from_signed_imm : b_source_type := "10";

   constant b_from_immX4      : b_source_type := "11";

--   type c_source_type is (from_null, from_alu, from_shift, 

--      from_mult, from_memory, from_pc, from_imm_shift16,

--      from_reg_source_nez, from_reg_source_eqz);

   subtype c_source_type is std_logic_vector(2 downto 0);

   constant c_from_alu        : c_source_type := "000";

   constant c_from_shift      : c_source_type := "001";

   constant c_from_mult       : c_source_type := "010";

   constant c_from_memory     : c_source_type := "011";

   constant c_from_pc         : c_source_type := "100";

   constant c_from_imm_shift16: c_source_type := "101";

   constant c_from_reg_sourcen: c_source_type := "110";

   constant c_from_null       : c_source_type := "111";

--   type pc_source_type is (from_inc4, from_inc8, from_reg_source, 

--      from_opcode25_0, from_branch, from_lbranch);

   subtype pc_source_type is std_logic_vector(1 downto 0);

   constant from_inc4       : pc_source_type := "00";

   constant from_opcode25_0 : pc_source_type := "01";

   constant from_branch     : pc_source_type := "10";

   constant from_lbranch    : pc_source_type := "11";

   subtype branch_function_type is std_logic_vector(2 downto 0);

   constant branch_ltz : branch_function_type := "000";

   constant branch_lez : branch_function_type := "001";

   constant branch_eq  : branch_function_type := "010";

   constant branch_ne  : branch_function_type := "011";

   constant branch_gez : branch_function_type := "100";

   constant branch_gtz : branch_function_type := "101";

   constant branch_yes : branch_function_type := "110";

   -- mode(32=1,16=2,8=3), signed, write

   subtype mem_source_type is std_logic_vector(3 downto 0);

   constant mem_none    : mem_source_type := "0000";

   constant mem_read32  : mem_source_type := "0100";

   constant mem_write32 : mem_source_type := "0101";

   constant mem_read16  : mem_source_type := "1000";

   constant mem_read16s : mem_source_type := "1010";

   constant mem_write16 : mem_source_type := "1001";

   constant mem_read8   : mem_source_type := "1100";

   constant mem_read8s  : mem_source_type := "1110";

   constant mem_write8  : mem_source_type := "1101";

   function bv_to_integer(bv: in std_logic_vector) return integer;

   function bv_adder(a     : in std_logic_vector(32 downto 0);

                     b     : in std_logic_vector(32 downto 0);

                     do_sub: in std_logic) return std_logic_vector;

   function bv_adder_lookahead(

                     a     : in std_logic_vector(32 downto 0);

                     b     : in std_logic_vector(32 downto 0);

                     do_sub: in std_logic) return std_logic_vector;

   function bv_negate(a : in std_logic_vector) return std_logic_vector;

   function bv_increment(a : in std_logic_vector(31 downto 2)

                     ) return std_logic_vector;

   function bv_inc6(a : in std_logic_vector

                     ) return std_logic_vector;

end; --package mips_pack

package body mips_pack is

function add_1(a:integer) return integer is

begin

   return a+1;

end; --function

function bv_to_integer(bv: in std_logic_vector) return integer is

   variable result : integer;

   variable b      : integer;

begin

   result := 0;

   b := 0;

   for index in bv'range loop

      if bv(index) = '1' then

         b := 1;

      else

         b := 0;

      end if;

      result := result * 2 + b;

   end loop;

   return result;

end; --function bv_to_integer

function bv_adder(a     : in std_logic_vector(32 downto 0);

                  b     : in std_logic_vector(32 downto 0);

                  do_sub: in std_logic) return std_logic_vector is

   variable carry_in : std_logic;

   variable bb       : std_logic_vector(32 downto 0);

   variable result   : std_logic_vector(32 downto 0);

begin

   result := "000000000000000000000000000000000";

   if do_sub = '0' then

      bb := b;

      carry_in := '0';

   else

      bb := not b;

      carry_in := '1';

   end if;

   for index in 0 to 32 loop

      result(index) := a(index) xor bb(index) xor carry_in;

      carry_in := (carry_in and (a(index) or bb(index))) or

                  (a(index) and bb(index));

   end loop;

   return result;

end; --function

function bv_adder_lookahead(

                  a     : in std_logic_vector(32 downto 0);

                  b     : in std_logic_vector(32 downto 0);

                  do_sub: in std_logic) return std_logic_vector is

   variable carry    : std_logic_vector(32 downto 0);

   variable p, g     : std_logic_vector(32 downto 0);

   variable bb       : std_logic_vector(32 downto 0);

   variable result   : std_logic_vector(32 downto 0);

   variable i        : natural;

begin

   carry := "000000000000000000000000000000000";

   if do_sub = '0' then

      bb := b;

      carry(0) := '0';

   else

      bb := not b;

      carry(0) := '1';

   end if;

   p := a or bb;   --propogate

   g := a and bb;  --generate

   for index in 0 to 7 loop

      i := index*4;

      carry(i+1) := g(i) or

                    (p(i) and carry(i));

      i := index*4+1;

      carry(i+1) := g(i) or

                    (p(i) and g(i-1)) or

                    ((p(i) and p(i-1)) and carry(i-1));

      i := index*4+2;

      carry(i+1) := g(i) or

                    (p(i) and g(i-1)) or

                    (p(i) and p(i-1) and g(i-2)) or

                    ((p(i) and p(i-1) and p(i-2)) and carry(i-2));

      i := index*4+3;

      carry(i+1) := g(i) or

                    (p(i) and g(i-1)) or

                    (p(i) and p(i-1) and g(i-2)) or

                    (p(i) and p(i-1) and p(i-2) and g(i-3)) or

                    (((p(i) and p(i-1)) and (p(i-2) and p(i-3)))

                       and carry(i-3));

   end loop;

   result := (a xor bb) xor carry;

   return result;

end; --function

function bv_negate(a : in std_logic_vector) return std_logic_vector is

   variable carry_in : std_logic;

   variable not_a    : std_logic_vector(31 downto 0);

   variable result   : std_logic_vector(31 downto 0);

begin

   result := ZERO;

   not_a := not a;

   carry_in := '1';

   for index in a'reverse_range loop

      result(index) := not_a(index) xor carry_in;

      carry_in := carry_in and not_a(index);

   end loop;

   return result;

end; --function

function bv_increment(a : in std_logic_vector(31 downto 2)

                     ) return std_logic_vector is

   variable carry_in : std_logic;

   variable result   : std_logic_vector(31 downto 2);

begin

   result := "000000000000000000000000000000";

   carry_in := '1';

   for index in 2 to 31 loop

      result(index) := a(index) xor carry_in;

      carry_in := a(index) and carry_in;

   end loop;

   return result;

end; --function

function bv_inc6(a : in std_logic_vector

                     ) return std_logic_vector is

   variable carry_in : std_logic;

   variable result   : std_logic_vector(5 downto 0);

begin

   result := "000000";

   carry_in := '1';

   for index in 0 to 5 loop

      result(index) := a(index) xor carry_in;

      carry_in := a(index) and carry_in;

   end loop;

   return result;

end; --function

end; --package body