Generate a pulse by using a counter/timer

Hi, thank you for your fast replies. I'll have a closer look at your suggestions and try to change my code accordingly. I'll report the outcome...

... with your help I just go the design running. I build an edge detector an used it to start my counter. Here is the code:

library ieee;
    use ieee.std_logic_1164.all;
entity edge_detector is
    port
    (
        clock         : in     std_logic;
        signal_in : in     std_logic;
        output     :   out std_logic
    );
end edge_detector;
architecture behavioral of edge_detector is
    signal signal_delayed : std_logic;
    
begin
    process (clock)
    begin
        if (rising_edge(clock)) then
            signal_delayed <= signal_in;
        end if;
    end process;
    output <= signal_in and (not signal_delayed);
end behavioral;

And following the updated code snippet of the ADC-Design:

    process(control_register_start_edge, counter_value)
    begin
        if (control_register_start_edge = '1') then
            counter_reset <= '0';
            counter_clock_enable <= '1';
            start <= '1';
        elsif (counter_value = x"00000004") then
            start <= '0';
            counter_clock_enable <= '0';
            counter_reset <= '1';
        end if;
    end process;

I was able to verify the design with ModelSim and even used the 'start' signal to blink an LED on my BeMicro CV ;)

No I am looking for a intelligent way to reset my register bit to '0' again. My first idea was to use a reset signal which would be detected in my r/w register process...

So after all, thank you for your help!