Electronic – How to convert a floating point number to integer, using VHDL

Please do not use the ieee.std_logic_arith library. It is outdated and makes problems when combining with others.

You can convert your signal as following:

library IEEE;
use IEEE.std_logic_1164.all;
use ieee.numeric_std.ALL;

signal counter: std_logic_vector(4 downto 0);

counter<=std_logic_vector(unsigned(counter) + 1);
            ...

   if (unsigned(counter) < to_unsigned(4, counter'length)) then

  -- do something

  end if;

If you plan to use a signal as a number most of the time, try to use type unsigned or signed if possible. You can always convert it to a std_logic_vector if needed.

Source: http://www.bitweenie.com/listings/vhdl-type-conversion/

EDIT:

I made a complete codesample that compiles and simulates in Vivado (should also work in modelsim):

library ieee;
use ieee.STD_LOGIC_1164.ALL;
use ieee.numeric_std.ALL;


entity test is
--  Port ( );
end test;

architecture Behavioral of test is
   signal counter: std_logic_vector(4 downto 0) := (others => '0');
   signal bigger: std_logic;
   signal clk: std_logic;
begin

make_clk: process
begin
    clk <= '0';
    wait for 2 ns;
    clk <= '1';
    wait for 2 ns;
end process;

test: process(clk)
begin
    if rising_edge(clk) then
        counter<=std_logic_vector(unsigned(counter) + 1);
        if (unsigned(counter) < to_unsigned(4, counter'length)) then
            --do something
            bigger <= '0';
        else
            bigger <= '1';
        end if;
    end if;
end process test;
end Behavioral;

In your disassembly we see calls to 64 bit (double precision) math functions:-

08001956:   bl 0x80004bc <__extendsfdf2>
...
0800195e:   bl 0x8000564 <__muldf3>
08001962:   bl 0x8000988 <__fixdfsi>

The STM32F4 only supports 32 bit floating point in hardware, so these functions must be done in software and will take many cycles to execute. To ensure that all calculations are done in 32 bit you should define all your floating point numbers (including constants) as type float.