VHDL Traffic Light Controller - vhdl

Question

Here is a simple code for a traffic light controller. It cycles through the states according to the counter values. However I would like it stay an additional 10 seconds on the first state when a pushbutton is pressed any ideas how I would do that.
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use ieee.std_logic_unsigned.all;
entity TLC is
Port (
Trafficlights: out STD_LOGIC_Vector (5 downto 0);
Clck : in STD_LOGIC;
Reset : in STD_LOGIC;
P_B : in STD_LOGIC);
end TLC;
architecture Behavioral of TLC is
type state_type is (st0_R1_G2, st1_R1_A1_A2, st2_G1_R2, st3_A1_R2_A2);
signal state: state_type;
signal count : std_logic_vector (3 downto 0);
constant sec10 : std_logic_vector ( 3 downto 0) := "1010";
constant sec2 : std_logic_vector (3 downto 0 ) := "0010";
constant sec16: std_logic_vector (3 downto 0 ) := "1111";
begin
process (Clck,Reset)
begin
if Reset='1' then
state <= st0_R1_G2; --reset to initial state
count <= X"0"; -- reset counter
elsif Clck' event and Clck = '1' then --rising edge
case (state) is ---state transitions
when st0_R1_G2 =>
if count < sec10 then
state <= st0_R1_G2;
count <= count + 1;
else
state <= st1_R1_A1_A2;
count <= X"0";
end if;
when st1_R1_A1_A2 =>
if count < sec2 then
state <= st1_R1_A1_A2;
count <= count + 1;
else
state <= st2_G1_R2;
count <= X"0";
end if;
when st2_G1_R2 =>
if count < sec10 then
state <= st2_G1_R2;
count <= count + 1;
else
state <= st3_A1_R2_A2;
count <= X"0";
end if;
when st3_A1_R2_A2 =>
if count < sec2 then
state <= st3_A1_R2_A2;
count <= count + 1;
else
state <=st0_R1_G2;
count <= X"0";
end if;
when others =>
state <= st0_R1_G2;
end case;
end if;
end process;
OUTPUT_DECODE: process (state)
begin
case state is
when st0_R1_G2 => Trafficlights <= "100001"; -- Traffic Red 1, Pedestrian Green 1
when st1_R1_A1_A2 => Trafficlights <= "110010";
when st2_G1_R2 => Trafficlights <= "001100";
when st3_A1_R2_A2 => Trafficlights <= "010110";
when others => Trafficlights <= "100001";
end case;
end process;
end Behavioral;

Answer 1

I haven't simulated this.
The idea is to extend the count counter by a bit encompassing the extra 10 seconds. The input p_b is used to asynchronously set a pushbutton event latch which is used to start an extended count, presumably allowing crosswalk traffic to traverse in the first 10 seconds.
It's controlled by a JK Flip flop (crosstime). The noticeable feature here should be that the cross walk is enabled for the first 10 seconds of the extended 20 sec period only. You don't give permission out of the blue to cross.
All this assumes your push button is an on demand pedestrian crossing request, you don't explain your state names nor your lights.
I'm guessing you'd want to gate the pedestrian green light with crosstime.
(And if this doesn't work or isn't what you wanted, you got what you paid for.)
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity tlc is
port (
trafficlights: out std_logic_vector (5 downto 0);
clck: in std_logic;
reset: in std_logic;
p_b: in std_logic
);
end entity tlc;
architecture behavioral of tlc is
type state_type is (st0_r1_g2, st1_r1_a1_a2, st2_g1_r2, st3_a1_r2_a2);
signal state: state_type;
signal count: std_logic_vector (4 downto 0) ; -- (3 downto 0);
signal pb_event: std_logic;
signal crosstime: std_logic; -- JK FF
constant sec10 : std_logic_vector (4 downto 0) := "01010"; -- ( 3 downto 0) := "1010";
constant sec2 : std_logic_vector (4 downto 0) := "00010"; -- (3 downto 0 ) := "0010";
-- constant sec16: std_logic_vector (4 downto 0) := "01111"; -- (3 downto 0 ) := "1111";
constant sec20: std_logic_vector (4 downto 0) := "10100"; -- new
begin
process (clck, reset, p_b) -- added push button
begin
if p_b = '1' and reset = '0' then -- asynch set for push button
pb_event <= '1';
end if;
if reset = '1' then
state <= st0_r1_g2; -- reset to initial state
count <= (others => '0'); -- reset counter
pb_event <= '0';
crosstime <= '0';
elsif clck' event and clck = '1' then -- rising edge
if pb_event = '1' and count = "00000" then -- J input
crosstime <= '1';
end if;
case (state) is -- state transitions
when st0_r1_g2 =>
if (crosstime = '0' and count < 20) or
(crosstime = '1' and count < sec10) then
state <= st0_r1_g2;
count <= count + 1;
else
state <= st1_r1_a1_a2;
count <= "00000"; -- x"0";
if crosstime = '1' then -- K input
crosstime <= '0';
pb_event <= '0';
end if;
end if;
when st1_r1_a1_a2 =>
if count < sec2 then
state <= st1_r1_a1_a2;
count <= count + 1;
else
state <= st2_g1_r2;
count <= (others => '0');
end if;
when st2_g1_r2 =>
if count < sec10 then
state <= st2_g1_r2;
count <= count + 1;
else
state <= st3_a1_r2_a2;
count <= (others => '0');
end if;
when st3_a1_r2_a2 =>
if count < sec2 then
state <= st3_a1_r2_a2;
count <= count + 1;
else
state <=st0_r1_g2;
count <= (others => '0');
end if;
when others =>
state <= st0_r1_g2;
end case;
end if;
end process;
output_decode:
process (state)
begin
case state is
when st0_r1_g2 => trafficlights <= "100001"; -- traffic red 1, pedestrian green 1
when st1_r1_a1_a2 => trafficlights <= "110010";
when st2_g1_r2 => trafficlights <= "001100";
when st3_a1_r2_a2 => trafficlights <= "010110";
when others => trafficlights <= "100001";
end case;
end process;
end architecture behavioral;
* ... Ive tried to synthesize this and I get and error saying "Signal pb_event cannot be synthesized, bad synchronous description. The description style you are using to describe a synchronous element (register, memory, etc.) is not supported in the current software release." Any ideas do you thik this is because its asynch and not compatible with the rest of the synchronous design ?*
Without knowing the vendor complaining about pb_even it sort of ties our hands.
It appears to be complaining about having both an asynchronous set and asynchronous reset on pb_event. Removing the asynchronous reset would likely cure the problem (the set is needed to tell us someone wants to use the crosswalk).
Let's move the pb_event flip flop out of the present process to make that available. The consequence of only using the set input is that a reset will set pb_event and cause a first crosswalk event.
Note I still don't understand the trafficlights and the modification I made in state st0_r1_g2 anticipates the crosswalk light is enabled during the first 10 seconds of the longer 20 second interval. That isn't included here.
Also you could simply equality compare count to the end counts, "/=" instead of "<" which might result is less count comparison logic. This can happen because count is always between 0 and an end count inclusively. Equality is a lot easier than magnitude comparison. I didn't make those changes either (and I'd be tempted to have separate recognizers for the count terminal values).
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity tlc is
port (
trafficlights: out std_logic_vector (5 downto 0);
clck: in std_logic;
reset: in std_logic;
p_b: in std_logic
);
end entity tlc;
architecture behavioral of tlc is
type state_type is (st0_r1_g2, st1_r1_a1_a2, st2_g1_r2, st3_a1_r2_a2);
signal state: state_type;
signal count: std_logic_vector (4 downto 0) ;
signal pb_event: std_logic;
signal crosstime: std_logic; -- JK FF
constant sec10 : std_logic_vector (4 downto 0) := "01010";
constant sec2 : std_logic_vector (4 downto 0) := "00010";
constant sec20: std_logic_vector (4 downto 0) := "10100";
begin
pbevent:
process (clck, reset, p_b)
begin
if p_b = '1' or reset = '1' then -- async set for push button
pb_event <= '1'; -- reset will give crosswalk event
elsif clck'event and clck = '1' then
if state = st0_r1_g2 and
(( crosstime = '1' and count = sec10) or count = sec20) then
pb_event <= '0';
end if;
end if;
end process;
unlabelled:
process (clck, reset)
begin
if reset = '1' then
state <= st0_r1_g2; -- reset to initial state
count <= (others => '0'); -- reset counter
crosstime <= '0';
elsif clck'event and clck = '1' then
if pb_event = '1' and count = "00000" then -- J input
crosstime <= '1';
end if;
case (state) is
when st0_r1_g2 =>
if (crosstime = '0' and count < sec20) or
(crosstime = '1' and count < sec10) then
state <= st0_r1_g2;
count <= count + 1;
else
state <= st1_r1_a1_a2;
count <= "00000";
if crosstime = '1' then -- K input
crosstime <= '0';
end if;
end if;
when st1_r1_a1_a2 =>
if count < sec2 then
state <= st1_r1_a1_a2;
count <= count + 1;
else
state <= st2_g1_r2;
count <= (others => '0');
end if;
when st2_g1_r2 =>
if count < sec10 then
state <= st2_g1_r2;
count <= count + 1;
else
state <= st3_a1_r2_a2;
count <= (others => '0');
end if;
when st3_a1_r2_a2 =>
if count < sec2 then
state <= st3_a1_r2_a2;
count <= count + 1;
else
state <=st0_r1_g2;
count <= (others => '0');
end if;
when others =>
state <= st0_r1_g2;
end case;
end if;
end process;
output_decode:
process (state)
begin
case state is
when st0_r1_g2 => trafficlights <= "100001"; -- traffic red 1, pedestrian green 1
when st1_r1_a1_a2 => trafficlights <= "110010";
when st2_g1_r2 => trafficlights <= "001100";
when st3_a1_r2_a2 => trafficlights <= "010110";
when others => trafficlights <= "100001";
end case;
end process;
end architecture behavioral;
The conditions found in state st0_r1_g2 have been collapsed to separately write a '0' to the pb_event flip flop. You might anticipate any time count = sec20 the flip flop should be cleared.