resltbitmask.vhd

ARM7核在FPGA中的VHDL代码实现

--****************************************************************************************************
-- This module cleares/sets bit 0 and clears 1 of ALU bus for ARM7TDMI-S processor
-- Designed by Ruslan Lepetenok
-- Modified 18.12.2002
--****************************************************************************************************
library	IEEE;
use IEEE.std_logic_1164.all;

entity ResltBitMask is port(
					   -- Data
	                   DataIn     : in  std_logic_vector(31 downto 0);
	                   DataOut    : out std_logic_vector(31 downto 0);
					   -- Control
					   ClrBitZero : in std_logic;
					   ClrBitOne  : in std_logic;
					   SetBitZero : in std_logic
	                  );
end ResltBitMask;

architecture RTL of ResltBitMask is
begin

DataOut(DataOut'high downto 2)<= DataIn(DataIn'high downto 2);	
	
DataOut(0) <= (DataIn(0) and not(ClrBitZero or SetBitZero))or -- Nomal mode (pass bit[0])
              SetBitZero;                                     -- Set bit[0] - Thumb mode Branch with link (LR bit[0]='1')

DataOut(1) <= '0' when ClrBitOne='1' else DataIn(1);

	
end RTL;