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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_register.vhd] - Rev 199
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-- Copyright (c)2006, 2016, 2019, 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 : o8_register -- Description: Provides a single addressible 8-bit register -- -- Register Map: -- Offset Bitfield Description Read/Write -- 0x00 AAAAAAAA Registered Outputs (RW) -- -- Revision History -- Author Date Change ------------------ -------- --------------------------------------------------- -- Seth Henry 12/20/19 Design Start library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; use ieee.std_logic_arith.all; use ieee.std_logic_misc.all; library work; use work.open8_pkg.all; entity o8_register is generic( Default_Value : DATA_TYPE := x"00"; Reset_Level : std_logic; Address : ADDRESS_TYPE ); port( Clock : in std_logic; Reset : in std_logic; -- Bus_Address : in ADDRESS_TYPE; Wr_Enable : in std_logic; Wr_Data : in DATA_TYPE; Rd_Enable : in std_logic; Rd_Data : out DATA_TYPE; -- Register_Out : out DATA_TYPE ); end entity; architecture behave of o8_register is 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; constant User_Addr : std_logic_vector(15 downto 0) := Address(15 downto 0); alias Comp_Addr is Bus_Address(15 downto 0); signal Addr_Match : std_logic; signal Wr_En : std_logic; signal Wr_Data_q : DATA_TYPE; signal Reg_Out : DATA_TYPE; signal Rd_En : std_logic; begin Addr_Match <= '1' when Comp_Addr = User_Addr else '0'; io_reg: process( Clock, Reset ) begin if( Reset = Reset_Level )then Wr_En <= '0'; Wr_Data_q <= (others => '0'); Reg_Out <= Default_Value; Rd_En <= '0'; Rd_Data <= OPEN8_NULLBUS; elsif( rising_edge( Clock ) )then Wr_En <= Addr_Match and Wr_Enable; Wr_Data_q <= Wr_Data; if( Wr_En = '1' )then Reg_Out <= Wr_Data_q; end if; Rd_Data <= OPEN8_NULLBUS; Rd_En <= Addr_Match and Rd_Enable; if( Rd_En = '1' )then Rd_Data <= Reg_Out; end if; end if; end process; Register_Out <= Reg_Out; end architecture;
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