LIBRARY IEEE;
USE IEEE.std_logic_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.all;

USE IEEE.STD_LOGIC_UNSIGNED.all; -- assumed in all the examples!

-----------------------------------------------
--timer, runs from timeval to 0, sets expired = 1
--when cnt = x"0000"
--max can be set with timeval is multiple of
--1,6ms
--if timeval is set to x0000 timer is stopped,
--expired signal always low
--refresh sets counter back to 0
-----------------------------------------------
--13.7.2006  inserted 4 bit offset, min timeout 1,6ms max timeout 104,86s
entity timeout is

port(
    --clock input
    clk_in   : in std_logic;
    refresh  : in std_logic;
    timeval  : in std_logic_vector(15 downto 0);
    EN       : in std_logic;
    --clock output
    expired : out std_logic
    );
end timeout;

architecture atimeout of timeout is

signal all0 : std_logic_vector(19 downto 0); --0x0000
signal cnt : std_logic_vector(19 downto 0);  --counter register
signal expired_i : std_logic;                  --internal expired
signal local_refr : std_logic;                 --internal slow clock refresh signal

begin
    
    all0 <=x"0000" & "1111";
    --converts fast clock asynchronous refresh to 
    --internal slow clock synchrouous local_refr
    process(clk_in, refresh)            
        begin
           if refresh = '1' then local_refr <= '1';
           elsif clk_in'event and clk_in = '1' then --sets refresh back to 0 at positive slope
            if EN = '1' then             
             local_refr <= '0'; ---hmm, works maybe
            end if;
           end if;
        end process;
    
    --generates the timeout
    process(clk_in)
        begin
            if clk_in'event and clk_in = '1' then
                if EN = '1' then
                    --if refresh, set counter to timeval, set exprired to 0
                    if local_refr='1' then
                        expired_i <= '0';
                        cnt <= timeval & "1111";
                    --if not expired and timeval < 0 decrement
                    elsif expired_i='0' and (timeval & "1111") /= all0 then
                        cnt <= cnt - 1;
                    end if;
                    --when counter is 0 set expired to 1
                    if cnt = all0 and (timeval & "1111") /= all0 then expired_i <= '1'; end if;
                end if;    
            end if;
    end process;
    expired <= expired_i;
end atimeout;