OK here is the code for my state machine. I am using it to control a serial multiplier in my circuit/
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity seq_mult_stateMachine is
port(clk, reset, start : in std_logic;
load_multiplier, shift_multiplier, load_multiplicand : out std_logic;
reset_product, load_product, shift_product : out std_logic;
done : out std_logic;
the_state : out std_logic_vector(1 downto 0); -- for debugging purpose only
counter_out : out std_logic_vector(3 downto 0)
);
end entity seq_mult_stateMachine;
architecture seq_mult_stateMachine_Architecture of seq_mult_stateMachine is
type theStat is (S0, S1, S2, S3);
signal present_state: theStat := S0;
signal next_state: theStat;
signal counter : std_logic_vector(3 downto 0);
begin
seq: process (clk) is
begin
if(rising_edge(clk)) then
if(reset = '1') then
present_state <= S0;
elsif(reset = '0') then
report "reached here";
present_state <= next_state;
end if;
end if;
end process seq;
com: process(start, present_state) is
begin
load_multiplier <= '0';
shift_multiplier <= '0';
load_multiplicand <= '0';
reset_product <= '0';
load_product <= '0';
shift_product <= '0';
done <= '0';
-- using signal the_state for debugging
case present_state is
when S0 => the_state <= "00";
when S1 => the_state <= "01";
when S2 => the_state <= "10";
when S3 => the_state <= "11";
end case;
--
case present_state is
when S0 =>
if(start = '1') then
--Initializing
load_multiplier <= '1';
load_multiplicand <= '1';
reset_product <= '1';
counter <= "0000";
next_state <= S1;
else
next_state <= S0;
end if;
when S1 =>
load_product <= '1';
counter <= counter + '1';
next_state <= S2;
when S2 =>
shift_product <= '1';
shift_multiplier <= '1';
if(counter = "1111") then
next_state <= S3;
else
next_state <= S1;
end if;
when S3 =>
done <= '1';
next_state <= S0;
when others =>
next_state <= S0;
end case;
counter_out <= counter;
end process;
end seq_mult_stateMachine_Architecture;
When I implemented it, it did Not work correctly. Thus I was forced to put the_state and counter_out signals for debugging purpose. When I run the simulation in Quartus with the other blocks and put the Start input, the output is shown in the Attachment.
Problem: My 'counter' variable goes crazy once the state S1 is entered, it keeps increasing regardless of the state being changed and finally I get the error of setup time violation. It should change ONLY when the state changes right? thats how I wrote the code.
Please tell me why this is happening I have used I integer before but the same result.
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