Honored Contributor
Honored ContributorHello Frank,
thanks for your interesting observation. I continued the investigation and try to summarize my results. I think the state machine viewer has a bug and the compiler inserts redundant logic in special cases: I used the code which I posted on January 11th, 2008 05:03 PM. I have 4 different versions:architecture performancetest of performancetest_1_fsm2conditions_2 is
type STATES is (init, green, yellow, red);
signal state : STATES;
signal reset_timer : std_logic;
signal timer_max : std_logic;
component timer
port(
clk : in std_logic;
reset : in std_logic;
reset_timer : in std_logic;
timer_max : out std_logic
);
end component;
begin
timer1:timer
port map (
clk => clk,
reset => reset,
reset_timer => reset_timer,
timer_max => timer_max
);
process(clk,reset)
variable reset_timer_var : std_logic;
begin
if reset = '1' then
output <= "00";
reset_timer_var := '0';
state <= init;
elsif clk'event and clk = '1' then
reset_timer_var := '0';
if trafficLight_ena = '0' then
reset_timer_var := '1';
state <= init;
else
case state is
when init =>
if trafficLight_ena = '1' then -- removed at version 3 & 4
output <= "00";
reset_timer_var := '1';
state <= red;
else -- removed at version 1 & 3 & 4
state <= init; -- removed at version 1 & 3 & 4
end if;
when green =>
output <= "01";
if timer_max = '1' and input = '0' then
state <= yellow;
else -- removed at version 1 & 3
state <= green; -- removed at version 1 & 3
end if;
when yellow =>
output <= "10";
reset_timer_var := '1';
state <= red;
when red =>
output <= "11";
if timer_max = '1' and input = '1' then
reset_timer_var := '1';
state <= green;
else -- removed at version 1 & 3
state <= red; -- removed at version 1 & 3
end if;
end case;
end if;
reset_timer <= reset_timer_var;
end if;
end process;
end performancetest;
init 0 0
green 0 1
yellow 1 0
red 1 1
init init (!trafficLight_ena)
init red (trafficLight_ena)
green init (!trafficLight_ena)
green green (!timer:timer1).(trafficLight_ena) + (timer:timer1).(input).(trafficLight_ena)
green yellow (timer:timer1).(!input).(trafficLight_ena)
yellow init (!trafficLight_ena)
yellow red (trafficLight_ena)
red init (!trafficLight_ena)
red green (timer:timer1).(input).(trafficLight_ena)
red red (!timer:timer1).(trafficLight_ena) + (timer:timer1).(!input).(trafficLight_ena)
