Subversion Repositories tinycpu

--Memory management component

--By having this separate, it should be fairly easy to add RAMs or ROMs later

--This basically lets the CPU not have to worry about how memory "Really" works

--currently just one RAM. 1024 byte blockram.vhd mapped as 0 - 1023

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.NUMERIC_STD.ALL;

entity top is

  port(

    Reset: in std_logic;

    Hold: in std_logic;

    HoldAck: out std_logic;

    Clock: in std_logic;

    DMA: in std_logic; --when high, Address, WriteEnable, and Data are connected to memory

    Address: in std_logic_vector(15 downto 0); --memory address (in bytes)

    WriteEnable: in std_logic;

    Data: inout std_logic_vector(15 downto 0);

    --debug ports

    DebugR0: out std_logic_vector(7 downto 0)

  );

end top;

architecture Behavioral of top is

  component memory is

    port(

      Address: in std_logic_vector(15 downto 0); --memory address (in bytes)

      WriteWord: in std_logic; --if set, will write a full 16-bit word instead of a byte. Address must be aligned to 16-bit address. (bottom bit must be 0)

      WriteEnable: in std_logic;

      Clock: in std_logic;

      DataIn: in std_logic_vector(15 downto 0);

      DataOut: out std_logic_vector(15 downto 0)

    );

  end component;

  component core is

    port(

      --memory interface 

      MemAddr: out std_logic_vector(15 downto 0); --memory address (in bytes)

      MemWW: out std_logic; --memory writeword

      MemWE: out std_logic; --memory writeenable

      MemIn: in std_logic_vector(15 downto 0);

      MemOut: out std_logic_vector(15 downto 0);

      --general interface

      Clock: in std_logic;

      Reset: in std_logic; --When this is high, CPU will reset within 1 clock cycles. 

      --Enable: in std_logic; --When this is high, the CPU executes as normal, when low the CPU stops at the next clock cycle(maintaining all state)

      Hold: in std_logic; --when high, CPU pauses execution and places Memory interfaces into high impendance state so the memory can be used by other components

      HoldAck: out std_logic; --when high, CPU acknowledged hold and buses are in high Z

      --todo: port interface

      --debug ports:

      DebugIR: out std_logic_vector(15 downto 0); --current instruction

      DebugIP: out std_logic_vector(7 downto 0); --current IP

      DebugCS: out std_logic_vector(7 downto 0); --current code segment

      DebugTR: out std_logic; --current value of TR

      DebugR0: out std_logic_vector(7 downto 0)

    );

  end component;

  signal cpuaddr: std_logic_vector(15 downto 0);

  signal cpuww: std_logic;

  signal cpuwe: std_logic;

  signal cpumemin: std_logic_vector(15 downto 0);

  signal cpumemout: std_logic_vector(15 downto 0);

  signal debugir: std_logic_vector(15 downto 0);

  signal debugip: std_logic_vector(7 downto 0);

  signal debugcs: std_logic_vector(7 downto 0);

  signal debugtr: std_logic;

  signal MemAddress: std_logic_vector(15 downto 0); --memory address (in bytes)

  signal MemWriteWord: std_logic; --if set, will write a full 16-bit word instead of a byte. Address must be aligned to 16-bit address. (bottom bit must be 0)

  signal MemWriteEnable: std_logic;

  signal MemDataIn: std_logic_vector(15 downto 0);

  signal MemDataOut: std_logic_vector(15 downto 0);

begin

  cpu: core port map (

    MemAddr => cpuaddr,

    MemWW => cpuww,

    MemWE => cpuwe,

    MemIn => cpumemin,

    MemOut => cpumemout,

    Clock => Clock,

    Reset => Reset,

    Hold => Hold,

    HoldAck => HoldAck,

    DebugIR => DebugIR,

    DebugIP => DebugIP,

    DebugCS => DebugCS,

    DebugTR => DebugTR,

    DebugR0 => DebugR0

  );

  mem: memory port map(

    Address => MemAddress,

    WriteWord => MemWriteWord,

    WriteEnable => MemWriteEnable,

    Clock => Clock,

    DataIn => MemDataIn,

    DataOut => MemDataOut

  );

  MemAddress <= cpuaddr when DMA='0' else Address;

  MemWriteWord <= cpuww when DMA='0' else '1';

  MemWriteEnable <= cpuwe when DMA='0' else WriteEnable;

  MemDataIn <= cpumemout when DMA='0' else Data when WriteEnable='1' else "ZZZZZZZZZZZZZZZZ";

  cpumemin <= MemDataOut;

  Data <= MemDataOut when DMA='1' and WriteEnable='0' else "ZZZZZZZZZZZZZZZZ";

end Behavioral;