Simple ALU block

synthesisable description with COMPASS ASIC synthetizer

prepared by P. Bakowski

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

LIBRARY COMPASS_LIB;

USE COMPASS_LIB.COMPASS.ALL;

use work.tms.all;

entity mon_alu is

port(oper:in Trois_BITs; operand1,operand2:in ADDR_BUS; ovm,setov,ovfl:in std_logic; ov:out std_logic; result:out ADDR_BUS);

end mon_alu;

architecture beh_mon_alu of mon_alu is

begin

process(oper,operand1,operand2,ovm,setov,ovfl) -- combinational process

variable res:ADDR_BUS;

begin

case oper is

when "111"=> res:=operand1 xor operand2;

when "110"=> res:=operand1 and operand2;

when "101"=> res:=operand1 or operand2;

when "100"=> res:=operand1 + operand2;

when "011"=> res:=operand1 - operand2;

when "010"=> res:=operand2;

when others=> res:=extend("0",32); -- extend function is used to generate the operands of required size (e.g. 32 bits)

end case;

if setov='1' then

ov<=ovfl;

elsif ((operand1(31)='0' and operand2(31)='0' and res(31)='1') or(operand1(31)='1' and operand2(31)='1'and res(31)='0')) and (oper="100" or oper="011") then

ov<='1'; else ov<='0';

end if;

if ((operand1(31)='0' and operand2(31)='0' and res(31)='1') or(operand1(31)='1' and operand2(31)='1'and res(31)='0')) and (ovm='1') then

if (res(31)='1') then

result(30 downto 0)<=sign_extend("1",31);

else

result(30 downto 0)<=extend("0",31);

end if;

result(31)<=not(res(31));

else

result(31 downto 0)<=res(31 downto 0);

end if;

end process;

end beh_mon_alu;

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