------------------------------------------------------------------------

-- File: speed.vhd

--

-- Group: Korrey Scott 237118

-- Milton Mah 341428

-- Mike Holden 346386

--

-- Course: EE 552

-- Project: ASM

-- Instructor: Dr. Duncan Elliott

-- Completed: Mar. 9, 1998

------------------------------------------------------------------------

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_unsigned.all;

------------------------------------------------------------------------

-- Entity: speed

--

-- Inputs: reset: connected to the master reset. Resets the speed

-- module to initial state.

-- seconds_pulse: a 1 Hertz pulse generated by clock.vhd

--

-- revolution: pulse generated by the rotation of the wheel

--

-- Outputs: velocity: the velocity of the automobile, in meters per second

-- determined by the rotation frequency and circumference

-- of the wheel

------------------------------------------------------------------------

entity speed is

generic ( circumference:positive:=2;

max_distance:positive:=127;

max_dist_minus_circ:positive:=125

);

port (

revolution, reset : in std_logic;

seconds_pulse : in std_logic;

velocity : out integer range 0 to max_distance

);

end speed;

------------------------------------------------------------------------

-- Architecture: behaviour of speed

--

-- Description: The purpose of this module is calculate the velocity

-- of the automobile, in meters per second.

------------------------------------------------------------------------

architecture behaviour of speed is

signal distance_gone : integer range 0 to max_distance;

signal reset_distance : std_logic;

signal start_distance : std_logic;

begin

get_velocity : process

variable velocity_bak : integer range 0 to max_distance;

begin

wait until rising_edge(seconds_pulse);

if reset = '1' then

reset_distance <= '1';

velocity <= 0;

elsif start_distance = '1' then

reset_distance <= '0';

else

velocity <= distance_gone;

reset_distance <= '1';

end if;

end process get_velocity;

get_distance : process

begin

wait until rising_edge(revolution);

if reset = '1' then

start_distance <= '0';

distance_gone <= 0;

elsif reset_distance = '1' then

distance_gone <= 0;

start_distance <= '1';

else

start_distance <= '0';

if distance_gone < max_dist_minus_circ then

distance_gone <= distance_gone + circumference;

end if;

end if;

end process get_distance;

end behaviour;