FATAL_ERROR: Iteration limit 10000 is reached

Question

It is over 2 weeks I faced a probem, Im programming an artix 7 FPGA. The process is simple:

• a serial module receive 2 bitstreams(2 bytes)
• Demux module according to these 2 bytes enable 2 bits in array puf_en

when I add demux module to the whoe design, during the simulation I receive this Error: FATAL_ERROR: Iteration limit 10000 is reached.

The code for demux is here:

    PUF_STATE_PROCESS:process(clk,uart_read,PUF_signal,UART_READ_FLAG)
begin
    if (rising_edge(clk)) then
        if (uart_read="11111111") then-- this means reset
                                stop_s<='0';

                                puf_signal<=initial;
                                reset_s<='1';
                                LED_S<="1111";

        else

            case puf_signal is
                    When initial=>
                              reset_s<='1';
                              puf_en_s<=(others=>'0');
                              LED_S<="0001";
                              --if   UART_READ_FLAG='1' then
                                if uart_read/="11111110" then

                                else
                                         stop_s<='0';

                                         puf_signal<=ch_i;                                   
                                end if;   
                            --   end if;      
                    When ch_i =>
                                if UART_READ="11111110" or UART_READ="11111111"  then

                                else
                                        ch_i_s<=(uart_read);

                                        puf_signal<=ch_j;
                                        LED_S<="0010";
                                end if;
                    when ch_j=>
                               if UART_READ="11111110" or UART_READ="11111111" or uart_read=ch_i_s  then

                               else
                               ch_j_s<=(uart_read);
                              mux_en_s_j<=uart_read;
                               puf_signal<=start;
                               timer_s<=(others=>'0');
                               LED_S<="0011";
                                end if;
                    when start=>
                                reset_s<='0';

                                if timer_start<10000 then
                                        mux_en_s_i<=ch_i_s;
                                        mux_en_s_j<=ch_j_s;
                                       timer_start<=timer_start+1;

                                        for i in 0 to (RO_Number) loop
                                            if i=ch_i_s then
                                                puf_en_s(i)<='1';                    
                                            elsif i=ch_j_s then

                                              puf_en_s(i)<='1';
                                            else
                                                puf_en_s(i)<='0';

                                             end if;
                                          end loop;            


                                       LED_S<="0100";
                                else

                                        puf_signal<=finish;
                                        timer_start<=0;
                                        LED_S<="0101";
                              end if;

                      when finish=>
                      if timer_s<timer_max_value then
                              timer_s<=timer_s+'1';

                              puf_en_s<=(others=>'0');
                              LED_S<="0100";
                      else
                             stop_s<='1'; 
                             timer_s<=(others=>'0');
                             LED_S<="0111";
                             puf_signal<=initial; 
                      end if;


            end case;
         end if;
    end if;
end process;

Can anyone tel me what is wrong with my code? i tested severa different approaches but I have this error.

Thanks

Answer 1

The main problem was not in this code.It was actually correlated to the Ring oscillators.In Ring Oscillators there was combinational loops with zero delay and it caused this problem