Subversion Repositories open8_urisc

-- Copyright (c)2006,2011,2012,2013,2015,2020 Jeremy Seth Henry
-- All rights reserved.
--
-- Redistribution and use in source and binary forms, with or without
-- modification, are permitted provided that the following conditions are met:
--     * Redistributions of source code must retain the above copyright
--       notice, this list of conditions and the following disclaimer.
--     * Redistributions in binary form must reproduce the above copyright
--       notice, this list of conditions and the following disclaimer in the
--       documentation and/or other materials provided with the distribution,
--       where applicable (as part of a user interface, debugging port, etc.)
--
-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``AS IS'' AND ANY
-- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-- DISCLAIMED. IN NO EVENT SHALL JEREMY SETH HENRY BE LIABLE FOR ANY
-- DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-- VHDL Units :  Open8_pkg
-- Description:  Contains constant definitions for the Open8 processor
--
-- Revision History
-- Author          Date     Change
------------------ -------- ---------------------------------------------------
-- Seth Henry      07/22/06 Design Start
-- Seth Henry      02/03/12 Updated generics to match current model
-- Seth Henry      10/29/15 Migrated type/constant definitions to this file
-- Seth Henry      03/09/20 Created new ALU/SP opcodes for handling new RSP
-- Seth Henry      03/12/20 Rationalized the naming of the CPU flags to match
--                           the assembler names. Also removed superfluous
--                           signals in the ALU and PC records.
-- Seth Henry      03/17/20 Added new subtype and constants for external
--                           GP flags.
-- Seth Henry      03/18/20 Added the ceil_log2 function, since it is used in
--                           memory sizing calculations.
-- Seth Henry      04/09/20 Added the I bit to the exported flags for use in
--                           memory protection schemes.
-- Seth Henry      04/16/20 Added the OPEN8_BUS_TYPE record to simplify
--                           peripheral connections.
-- Seth Henry      10/21/20 Modified the write data path to use separate
--                           enumerated states rather than reuse the .reg field
--                           to improve performance.
-- Seth Henry      10/23/20 Moved CPU internal constants to o8_cpu.vhd
 
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
 
package Open8_pkg is
 
-------------------------------------------------------------------------------
-- External constants and type declarations
--
-- These subtypes can be used with external peripherals to simplify
--  connection to the core.
-------------------------------------------------------------------------------
 
  -- These must never be changed, as the core requires them to be these static
  --  values for proper operation. These are ONLY defined here to allow user
  --  code to dynamically configure itself to match the Open8 core.
 
  constant OPEN8_ADDR_WIDTH  : integer := 16; -- DON'T EVEN CONTEMPLATE
  constant OPEN8_DATA_WIDTH  : integer := 8;  -- CHANGING THESE!
 
  subtype ADDRESS_TYPE is std_logic_vector(OPEN8_ADDR_WIDTH - 1 downto 0);
  subtype DATA_TYPE    is std_logic_vector(OPEN8_DATA_WIDTH - 1 downto 0);
  -- Note: INTERRUPT_BUNDLE must be exactly the same width as DATA_TYPE
  subtype INTERRUPT_BUNDLE is DATA_TYPE;
 
  subtype EXT_GP_FLAGS is std_logic_vector(4 downto 0);
 
  constant EXT_ISR           : integer := 0;
  constant EXT_GP4           : integer := 1;
  constant EXT_GP5           : integer := 2;
  constant EXT_GP6           : integer := 3;
  constant EXT_GP7           : integer := 4;
 
  constant OPEN8_NULLBUS     : DATA_TYPE := x"00";
 
  constant Reset_Level       : std_logic := '1';
 
  type OPEN8_BUS_TYPE is record
    Clock                    : std_logic;
    Reset                    : std_logic;
    uSec_Tick                : std_logic;
    Address                  : ADDRESS_TYPE;
    Wr_En                    : std_logic;
    Wr_Data                  : DATA_TYPE;
    Rd_En                    : std_logic;
    GP_Flags                 : EXT_GP_FLAGS;
  end record;
 
  constant INIT_OPEN8_BUS    : OPEN8_BUS_TYPE := (
                                 '0',           -- Clock
                                 Reset_Level,   -- Reset
                                 '0',           -- uSec_Tick
                                 x"0000",       -- Address
                                 '0',           -- Wr_En
                                 OPEN8_NULLBUS, -- Wr_Data
                                 '0',           -- Rd_En
                                 "00000"        -- GP_Flags
                               );
 
  -- Component declaration
  --  (assumes a 1K RAM at 0x0000 and ROM at the top of the memory map)
  component o8_cpu is
  generic(
    Program_Start_Addr       : ADDRESS_TYPE := x"8000";
    ISR_Start_Addr           : ADDRESS_TYPE := x"FFF0";
    Stack_Start_Addr         : ADDRESS_TYPE := x"03FF";
    Allow_Stack_Address_Move : boolean      := false;
    Enable_Auto_Increment    : boolean      := false;
    BRK_Implements_WAI       : boolean      := false;
    Enable_NMI               : boolean      := true;
    RTI_Ignores_GP_Flags     : boolean      := false;
    Default_Interrupt_Mask   : DATA_TYPE    := x"FF";
    Clock_Frequency          : real
  );
  port(
    Clock                    : in  std_logic;
    PLL_Locked               : in  std_logic;
    Halt_Req                 : in  std_logic := '0';
    Halt_Ack                 : out std_logic;
    Open8_Bus                : out OPEN8_BUS_TYPE;
    Rd_Data                  : in  DATA_TYPE;
    Interrupts               : in  INTERRUPT_BUNDLE := x"00"
  );
  end component;
 
  -- This function is used to calculate RAM parameters, but is generally
  --  useful for making things more generic.
  function ceil_log2 (x : in natural) return natural;
 
end package;
 
package body Open8_pkg is
 
  -- The ceil_log2 function returns the minimum register width required to
  --  hold the supplied integer.
  function ceil_log2 (x : in natural) return natural is
    variable retval          : natural;
  begin
    retval                   := 1;
    while ((2**retval) - 1) < x loop
      retval                 := retval + 1;
    end loop;
    return retval;
  end function;
 
end package body;