Trying to verify Verilog/VHDL designs with formal methods and tools
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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
entity alu is
generic (
Width : natural := 8;
Formal : boolean := true
);
port (
Reset_n_i : in std_logic;
Clk_i : in std_logic;
Opc_i : in std_logic_vector(1 downto 0);
DinA_i : in std_logic_vector(Width-1 downto 0);
DinB_i : in std_logic_vector(Width-1 downto 0);
Dout_o : out std_logic_vector(Width-1 downto 0);
OverFlow_o : out std_logic
);
end entity alu;
architecture rtl of alu is
subtype t_opc is std_logic_vector(Opc_i'range);
constant c_add : t_opc := "00";
constant c_sub : t_opc := "01";
constant c_and : t_opc := "10";
constant c_or : t_opc := "11";
begin
process (Reset_n_i, Clk_i) is
variable v_result : std_logic_vector(Width downto 0);
begin
if (Reset_n_i = '0') then
v_result := (others => '0');
Dout_o <= (others => '0');
OverFlow_o <= '0';
elsif (rising_edge(Clk_i)) then
case Opc_i is
when c_add =>
v_result := std_logic_vector(unsigned('0' & DinA_i) +
unsigned('0' & DinB_i));
when c_sub =>
v_result := std_logic_vector(unsigned('0' & DinA_i) -
unsigned('0' & DinB_i));
when c_and => v_result := ('0', DinA_i and DinB_i);
when c_or => v_result := ('0', DinA_i or DinB_i);
when others => null;
end case;
Dout_o <= v_result(Width-1 downto 0);
OverFlow_o <= v_result(Width);
end if;
end process;
FormalG : if Formal generate
function max(a, b: std_logic_vector) return unsigned is
begin
if unsigned(a) > unsigned(b) then
return unsigned(a);
else
return unsigned(b);
end if;
end function max;
begin
default clock is rising_edge(Clk_i);
-- Initial reset
INITIAL_RESET : restrict {not Reset_n_i[*2]; Reset_n_i[+]}[*1];
AFTER_RESET : assert always
not Reset_n_i -> Dout_o = (Dout_o'range => '0') and OverFlow_o = '0';
ADD_OP : assert always Reset_n_i and Opc_i = c_add ->
next unsigned(Dout_o) = unsigned(prev(DinA_i)) + unsigned(prev(DinB_i)) abort not Reset_n_i;
SUB_OP : assert always Reset_n_i and Opc_i = c_sub ->
next unsigned(Dout_o) = unsigned(prev(DinA_i)) - unsigned(prev(DinB_i)) abort not Reset_n_i;
AND_OP : assert always Reset_n_i and Opc_i = c_and ->
next Dout_o = (prev(DinA_i) and prev(DinB_i)) abort not Reset_n_i;
OR_OP : assert always Reset_n_i and Opc_i = c_or ->
next Dout_o = (prev(DinA_i) or prev(DinB_i)) abort not Reset_n_i;
OVERFLOW_ADD : assert always Reset_n_i and Opc_i = c_add and (unsigned(DinA_i) + unsigned(DinB_i)) < max(DinA_i, DinB_i) ->
next OverFlow_o abort not Reset_n_i;
NOT_OVERFLOW_ADD : assert always Reset_n_i and Opc_i = c_add and (unsigned(DinA_i) + unsigned(DinB_i)) >= max(DinA_i, DinB_i) ->
next not OverFlow_o abort not Reset_n_i;
OVERFLOW_SUB : assert always Reset_n_i and Opc_i = c_sub and (unsigned(DinA_i) - unsigned(DinB_i)) > unsigned(DinA_i) ->
next OverFlow_o abort not Reset_n_i;
NOT_OVERFLOW_SUB : assert always Reset_n_i and Opc_i = c_sub and (unsigned(DinA_i) - unsigned(DinB_i)) <= unsigned(DinA_i) ->
next not OverFlow_o abort not Reset_n_i;
end generate FormalG;
end architecture rtl;