addr_combo_rtl.vhd

design compile synthesis user guide

-----------------------------------------------------------------
-- Combinational address block for RTL Analyzer tutorial
-- dependant on DATAPATH package
-----------------------------------------------------------------
-- Revision 1.3  1998/06/08  dannyb
-- format
--
-- Revision 1.2  1997/03/06  baldrik
-- use datatypes
--
-- Revision 1.1  1997/02/08  baldrik
-- Initial revision
-----------------------------------------------------------------

library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.std_logic_unsigned.all;
use work.DATAPATH.all;

architecture rtl of addr_combo is

constant ADDRESS_width : natural := 32;
subtype ADDRESS_TYPE is std_logic_vector(ADDRESS_width-1 downto 0);

signal  ADDRESS          : ADDRESS_TYPE;
signal  TRANSFER_COUNT   : CNT_TYPE;
signal  WORD_COUNT_read  : CNT_TYPE;
signal  WORD_COUNT_write : CNT_TYPE;
signal  WORD_COUNT       : CNT_TYPE;
signal  POINTER          : POINT_TYPE;
signal  LOW              : std_logic_vector(3 downto 0);
signal  DOUT_I           : ADDRESS_TYPE;


begin

  ADDR_PROC:
  process (BASE, INST_OFFSET, READ_OFFSET, WRITE_OFFSET, ENABLE_SELECT, LOW,
	    WRITE_POINTER, READ_POINTER) 
  begin
    case ENABLE_SELECT is
      when "001" =>
	LOW                  <= INST_OFFSET(15 downto 12);
	ADDRESS(11 downto 0) <= INST_OFFSET(11 downto 0);
	 
      when "101" =>
	LOW                  <= WRITE_OFFSET(15 downto 12);
	ADDRESS(11 downto 0) <= WRITE_OFFSET(11 downto 0);
	 
      when Others =>
	LOW                  <= READ_OFFSET(15 downto 12);
	ADDRESS(11 downto 0) <= READ_OFFSET(11 downto 0);
    end case;
	
    ADDRESS(31 Downto 12) <= BASE + LOW;

    if ENABLE_SELECT="111" then
       POINTER  <= WRITE_POINTER;
    else
       POINTER  <= READ_POINTER;
    end if;

  end process ADDR_PROC;

  WORD_COUNT <= datapath( POINTER => POINTER, ADDR => ADDR);

  TCOUNT: process(WORD_COUNT, ENABLE_SELECT) 
  begin
    
    if ((ENABLE_SELECT="001") 
      or (ENABLE_SELECT="010") 
      or (ENABLE_SELECT="100")) then
       TRANSFER_COUNT(10 downto 0) <= "00000000001";
    else
       TRANSFER_COUNT(10 downto 0) <= WORD_COUNT;
    end if;
  end process TCOUNT;

  SEL_DOUT: process(ADDRESS, TRANSFER_COUNT, DOUT_SELECT ) 
  begin
    if (DOUT_SELECT='1') then
      DOUT_I <= ADDRESS;
    else
      DOUT_I <= (others => '0');
      DOUT_I(10 downto 0) <= TRANSFER_COUNT;
    end if;
  end process SEL_DOUT;

  -- tristate DOUT
  DOUT <= DOUT_I when BUS_ENABLE = '1'
          else (others => 'Z');

end rtl;