--------------------------------------------------
-- Model        :   8051 Behavioral Model,
--                  VHDL Entity mc8051.inter_ctrl.interface
--
-- Author       :   Michael Mayer (mrmayer@computer.org),
--                  Dr. Hardy J. Pottinger,
--                  Department of Electrical Engineering
--                  University of Missouri - Rolla
--
-- Created at   :   10/24/98 13:45:19
--
LIBRARY ieee ;
USE ieee.std_logic_1164.all;
USE ieee.numeric_std.all;
LIBRARY mc8051 ;
USE mc8051.synth_pack.all;

ENTITY inter_ctrl IS
   PORT( 
      P0 : IN     std_logic_vector( 7 DOWNTO 0 )  ;
      acknow : IN     std_logic ;
      cycle_states : IN     std_logic_vector( 3 DOWNTO 0 )  ;
      dptr : IN     std_logic_vector( 15 DOWNTO 0 )  ;
      ea_n : IN     std_logic ;
      int_clk : IN     std_logic ;
      int_rst : IN     std_logic ;
      ir : IN     std_logic_vector( 7 DOWNTO 0 )  ;
      last_cycle : IN     std_logic ;
      pdat_loc : IN     std_logic_vector( 15 DOWNTO 0 )  ;
      rom_data : IN     std_logic_vector( 7 DOWNTO 0 )  ;
      rs : IN     std_logic_vector( 1 DOWNTO 0 )  ;
      addr_gb : OUT    std_logic_vector( 7 DOWNTO 0 )  ;
      ale : OUT    std_logic ;
      indirect_sel : OUT    std_logic ;
      p0_addr : OUT    std_logic_vector( 7 DOWNTO 0 )  ;
      p0_ctrl : OUT    std_logic ;
      p2_addr : OUT    std_logic_vector( 7 DOWNTO 0 )  ;
      p2_ctrl : OUT    std_logic ;
      pdata : OUT    std_logic_vector( 7 DOWNTO 0 )  ;
      psen_n : OUT    std_logic ;
      rd_gb : OUT    std_logic ;
      rd_n : OUT    std_logic ;
      rd_n_ctrl : OUT    std_logic ;
      rom_rd_n : OUT    std_logic ;
      wr_gb : OUT    std_logic ;
      wr_n : OUT    std_logic ;
      wr_n_ctrl : OUT    std_logic ;
      data_gb : INOUT  std_logic_vector( 7 DOWNTO 0 ) 
   );

-- Declarations

END inter_ctrl ;
--
-- VHDL Architecture mc8051.inter_ctrl.spec
--
-- Created:
--          by - mrmayer.UNKNOWN (eceultra18.ece.umr.edu)
--          at - 22:34:31 08/26/98
--
-- Generated by Mentor Graphics' Renoir(TM) 3.0 (Build 110)
--

-- Description
--    inter_ctrl is responsible for the interface control
--    of the 8051.  This includes all timing for the folloing
--    ports:
--        ALE
--        PSEN_N
--        RD_N
--        WR_N
--        P0 (in addr / data mode)
--        P2 (in addr mode)
--
--    It is tied to input port EA_N. 
--
--    Additional I/O include:
--        pdat_loc (IN)   - location in program data
--        dptr            - location for MOVX DPTR 
--        addr_gb, data_gb, rd_gb, wr_gb, acknow


ARCHITECTURE spec OF inter_ctrl IS

  -- a latched, X01 version of ea_n
  SIGNAL ea_n_int  : std_logic;
  SIGNAL ale_int   : std_logic;
  SIGNAL psen_n_int, rd_n_int, wr_n_int : std_logic;
  SIGNAL rom_rd_n_int : std_logic;
  SIGNAL ia_pmem, ea_pmem, rd_xmem, wr_xmem : std_logic;
  SIGNAL use_reg   : std_logic;
  SIGNAL reg_value : std_logic_vector(7 DOWNTO 0);
  SIGNAL data_byte : std_logic_vector(7 DOWNTO 0);
  SIGNAL p0_alt, p2_alt : std_logic_vector(7 DOWNTO 0);

BEGIN
  rd_n <= rd_n_int;
  wr_n <= wr_n_int;
  psen_n <= psen_n_int;
  ale <= ale_int;
  p0_addr <= p0_alt;
  p2_addr <= p2_alt;
  rom_rd_n <= rom_rd_n_int;
  pdata <= data_byte;

  ea_n_int     <= to_X01(ea_n) WHEN rising_edge(int_clk) AND (
                              cycle_states = s1p1 OR cycle_states = s4p1 ) ELSE 
                              ea_n_int;

  rd_xmem <= '1' WHEN std_match(ir,"1110001-") OR std_match(ir,"11100000") ELSE 
             '0';
  wr_xmem <= '1' WHEN std_match(ir,"1111001-") OR std_match(ir,"11110000") ELSE 
             '0';
  use_reg <= '1' WHEN std_match(ir,"111-001-") ELSE 
             '0';
  -- the next signal will change only at s1p1 or s4p1
  ia_pmem <= '1' WHEN ea_n_int = '1' AND unsigned(pdat_loc) < 16#1000# ELSE 
             '0';
  ea_pmem <= '1' WHEN (rd_xmem = '0' AND wr_xmem = '0') AND ia_pmem = '0' ELSE 
             '0';

  -- use the global bus to read the register r0 or r1 for an address, and
  -- to read / write the accumulator for a data value
  addr_gb <= "000" & rs & "00" & ir(0) WHEN (use_reg = '1' AND last_cycle = '0') AND 
                    (cycle_states = s3p1 OR cycle_states = s3p2) ELSE
             "11100000" WHEN ((wr_xmem = '1' AND last_cycle = '0') AND
                    (cycle_states = s4p1 OR cycle_states = s4p2))  OR
                    ((rd_xmem = '1' AND last_cycle = '1') AND
                    (cycle_states = s4p1 OR cycle_states = s4p2)) ELSE (OTHERS => 'Z');
  rd_gb   <=  '1' WHEN     (wr_xmem = '1' AND last_cycle = '0') AND
                    (cycle_states = s4p1 OR cycle_states = s4p2) ELSE
              'Z';
  wr_gb   <=  '1' WHEN     (rd_xmem = '1' AND last_cycle = '1') AND
                    (cycle_states = s4p1 OR cycle_states = s4p2) ELSE
              'Z';
  data_gb <=   data_byte WHEN (rd_xmem = '1' AND last_cycle = '1') AND
                    (cycle_states = s4p1 OR cycle_states = s4p2) ELSE
              (OTHERS => 'Z');
  reg_value <= data_gb WHEN (wr_xmem = '1' AND last_cycle = '0') AND acknow = '1' ELSE
               reg_value;

  -- drive the internal versions of the handshaking signals
  ale_int <=  '1' WHEN ((cycle_states = s2p1 OR cycle_states = s2p2) AND ea_pmem = '1') OR
                       ((cycle_states = s5p1 OR cycle_states = s5p2) AND 
                             (ea_pmem = '1' OR rd_xmem = '1' OR wr_xmem = '1'))
                          ELSE
                '0';

  -- psen_n is set low when doing program fetches.  This happens at s3p1 and s6p1 when
  -- there is no external read /write occurring.  It also happens at s6p1 of the last cycle
  -- of an external read / write when the internal memory accessing is not being used.
  psen_n_int <= '0' WHEN ((cycle_states = s3p1 OR cycle_states = s3p2 OR cycle_states = s4p1)
                            AND ea_pmem = '1')  OR
                         ((cycle_states = s6p1 OR cycle_states = s6p2 OR cycle_states = s1p1) AND
                            (ea_pmem = '1' OR (last_cycle = '1' AND ia_pmem = '0')))
                            ELSE
                '1'; 

  rom_rd_n_int   <= '0' WHEN (falling_edge(int_clk) AND ia_pmem = '1') AND
                         (cycle_states = s3p1 OR cycle_states = s6p1) ELSE
                '1' WHEN falling_edge(int_clk) AND 
                         (cycle_states = s1p2 OR cycle_states = s4p2) ELSE
                rom_rd_n_int;

  rd_n_int   <= '0' WHEN (falling_edge(int_clk) AND rd_xmem = '1') AND
                         (last_cycle = '1' AND cycle_states = s1p1) ELSE
                '1' WHEN (falling_edge(int_clk) AND cycle_states = s4p1) ELSE
                rd_n_int;

  wr_n_int   <= '0' WHEN (falling_edge(int_clk) AND wr_xmem = '1') AND
                         (last_cycle = '1' AND cycle_states = s1p1) ELSE
                '1' WHEN (falling_edge(int_clk) AND cycle_states = s4p1) ELSE
                wr_n_int;

  p2_alt    <= (OTHERS => '0') WHEN int_rst = '1' ELSE
                dptr(15 DOWNTO 8) WHEN (falling_edge(int_clk) AND cycle_states = s5p1) AND
                                       ((rd_xmem = '1' OR wr_xmem = '1') AND use_reg = '0') ELSE
                pdat_loc(15 DOWNTO 8) WHEN (falling_edge(int_clk) AND (
                          (cycle_states = s2p1 AND ea_pmem = '1') OR
                          (cycle_states = s5p1 AND (
                             ea_pmem = '1' OR (last_cycle = '1' AND ia_pmem = '0') ))
                           )) ELSE
                p2_alt;

  -- take control of p2 whenever external access of pmem is enabled, or
  -- when we are in (cycle 1 s5p1) through (cycle 2 s4p2) of external data rd / wr
  p2_ctrl    <= '1' WHEN ea_pmem = '1' OR ( (
              (last_cycle = '0' AND std_match(cycle_states,"11--")) OR
              (last_cycle = '1' AND (NOT std_match(cycle_states,"11--"))) ) AND 
                      (wr_xmem = '1' OR rd_xmem = '1')  ) ELSE 
                '0';

  p0_alt     <= (OTHERS => '0') WHEN int_rst = '1' ELSE
                dptr(7 DOWNTO 0) WHEN (rising_edge(int_clk) AND cycle_states = s5p1) AND
                                      ((rd_xmem = '1' OR wr_xmem = '1') AND use_reg = '0') ELSE
                reg_value        WHEN (rising_edge(int_clk) AND cycle_states = s5p1) AND
                                      ((rd_xmem = '1' OR wr_xmem = '1') AND use_reg = '1') ELSE
                pdat_loc(7 DOWNTO 0) WHEN  (cycle_states = s2p1 AND ea_pmem = '1') OR
                          (cycle_states = s5p1 AND (
                             ea_pmem = '1' OR (last_cycle = '1' AND ia_pmem = '0') ))
                            ELSE
                p0_alt;

  -- everytime this is set high, it sets all bits in the P0 sfr
  p0_ctrl    <= '1' WHEN ( ea_pmem = '1' AND ((cycle_states = s2p1 OR cycle_states = s2p2) OR
                                              (cycle_states = s5p1 OR cycle_states = s5p2)) )
                              OR
                         ( rd_xmem = '1' AND last_cycle = '0' AND (
                                              (cycle_states = s5p1 OR cycle_states = s5p2) OR
                                               cycle_states = s6p1 ) )
                              OR
                          -- wr_xmem from states (cycle 1, s5p1) to (cycle 2, s4p2)
                         ( wr_xmem = '1' AND ( (last_cycle = '0' AND std_match(cycle_states,"11--")) OR
                                 (last_cycle = '1' AND (cycle_states(3) = '1' XOR cycle_states(2) = '1') ) ))
                              OR
                         ( ia_pmem = '0' AND last_cycle = '1' AND
                                (cycle_states = s5p1 OR cycle_states = s5p2)) ELSE
                 '0';

  data_byte <= to_x01(p0)  WHEN rising_edge(int_clk) AND (
                            ((cycle_states = s1p1 OR cycle_states = s4p1) AND psen_n_int = '0') OR
                            ((last_cycle = '1' AND cycle_states = s3p1) AND rd_n_int = '0') ) ELSE
               rom_data WHEN rising_edge(int_clk) AND (
                            (cycle_states = s1p1 OR cycle_states = s4p1) AND ia_pmem = '1' )  ELSE
               data_byte;

END ARCHITECTURE spec;