led_emu.vhd

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-------------------------------------------------------------------------------
--! @file
--! @author Hipolito Guzman-Miranda
--! @brief Emulates on-board leds.
-------------------------------------------------------------------------------

--! Use IEEE standard definitions library
library ieee;
--! Use std_logic* signal types
use ieee.std_logic_1164.all;
--! Use the slv2string function present in the vhdl_verification package
use work.vhdl_verification.all;

--! @brief Emulates on-board leds
--!
--! @details Checks for events on \c led_input port, and reports the current
--! state of the leds each time any the input bit changes. Does not keep any
--! internal memory, \c led_input is assumed to be directly connected to the
--! leds.
entity led_emu is
  generic (
    ACTIVE_VALUE : std_logic := '0'; --! Led polarity
    NUM_LEDS     : integer   := 4    --! How many leds are we emulating
  );
  port (
    led_input : in  std_logic_vector(NUM_LEDS-1 downto 0)  --! Connect here the signal that drives the leds
  );
end led_emu;

--! @brief Architecture is based on just a single process
--!
--! @detailed An assertion has also been added to check that \c ACTIVE_VALUE is
--! set to a non-ambiguous strong value (either '0' or '1').
architecture led_emu_arch of led_emu is

begin

  -- ACTIVE_VALUE must be either '0' or '1' (no other values supported)
  assert ACTIVE_VALUE = '0' or ACTIVE_VALUE = '1'
    report "led_emu: ACTIVE_VALUE must be either '0' or '1'"
    severity failure;

  --! @brief Report led state each time there is an event in \c led_input
  --!
  --! @detailed We don't actually need to check for \c led_input'event, since
  --! putting \c led_input in the sensitivity list of the process does it for
  --! us. We use the report statement to print a string to the simulation log,
  --! and the slv2string function in the vhdl_verification package to convert
  --! the std_logic_vector value to a printable string.
  process (led_input)
  begin
    report "led_emu: current state of leds: " & slv2string(led_input);
  end process;

end led_emu_arch;