An EE476 project by Edward Mengel
Introduction:
The basis of this project is to create the game fish on the Atmel board. In the game fish, the big fish eat the small fish, so your job is to eat the fish smaller than you while not getting eaten by those bigger than you. You “eat” a fish by moving close enough to touch the fish, and if a larger fish gets close enough to touch you, you will be eaten. Furthermore, much like your mother told you in kindergarten, if you eat, you’ll get bigger.
For
this project I wrote the display driver and game logic in VHDL on the Altera
UP1 board. I wrote the controller input decoder and the game state logic
in C to be put on an Atmel board. The other components needed for this
project are the display and the controller.
Display:
I
have decided to attempt to generate an VGA signal to use as the display
for this device. This will make it possible to play fish on any household
Computer Monitor. The signal generated will have 3 bit color.
Controller:
I
have decided to use a SEGA Genesis control pad due to the availability
of the controller and it’s ergonomic design. The pinout
is also readily available and simple to use.
High
Level Design:
The
Controller communicates to the Atmel board through a 9-pin connection shown
here. I connected this to Port D of the Atmel Board. The Atmel board uses
this information to modify the current state of the fish you are controlling,
then randomly changes the states of the other 3 fish. The controller can
also send a Reset signal which will reset the Altera board. Activated by
pressing the Start button.
Program
Hardware Design:
Atmel
Board:
The
Atmel board reads the input from the controller more specifically up, down,
left, and right. And If this inputs vary from the fishes current state
the fishes current state will be changed. The fishes current direction
is represented with the lowest order bits of Port D, and the fish can only
move on the diagonal, and the fish must always be moving. So at any one
time the fish is either moving left or right (bit 1) and either moving
up or down (bit 0). Timer 0’s prescale is set to 64 and reloaded at 256-62
so that it overflows once per ms. Then a read controller task is performed
every 250 ms. Bits 2 through 5 are random to generate the direction of
the three other fish (one extra bit for expansion). These bits are randomized
by reading Timer 1. Timer one is set to the same prescale as Timer 0 (64),
but it is reloaded to 1, so that it’s value has no dependence on Timer
0 (every loop should offset the timers by 1 more than the last). The four
bits are determined by bitwise and’ing the first four bits with the last
four bits of the Timer. This value is saved as “rand.” The current rand
is bitwise and’ed with the old value of rand and this new value is bitwise
xor’ed with the old values of bits 2 through 5. This causes a bit to change
on average every 4 seconds. So that a fishes direction won’t be too random.
Port D bit 7 is the Reset signal which is only high while the Start button
is pressed.
Altera
Board:
The
Altera board uses it’s 25.175 MHz clock signal to generate H-synch and
V-synch pulses for the VGA display. It also stores the coordinates and
size of every fish on screen. Once every time the screen is refreshed the
Altera board updates each fishes coordinates depending on the direction
of each fish (the randomly controlled fish only move left or right). The
coordinate of the fish are checked to see if the fish is moving off the
screen, and if so it will wrap around to the other side. There is also
collision detection. If your fish collides with a bigger fish, the game
ends. The screen will freeze until it is Reset. If your fish collides with
a fish of equal or lesser size that fish is eaten, and the fish’s position
will be Reset. For every fish you eat your, score increases proportionally
to the size of the fish, and your own size is dependant on your score.
Performance:
The
speed and timing of the game same to operate at a level comparable to that
of human reaction. The controller input can seem a bit sluggish at times.
All of the fish move at the same speed (If you discard the fact that the
users fish moves diagonally) which adds a reasonable amount of challenge
to the game.
Possible
Updates or Modifications:
The
limits of the UP1 board were clearly close to being reached as was shown
by the “less than 20% of logic circuits remaining” warning message, so
any future upgrades could possibly require a larger gate array. The limits
of the timing of the UP1 board were also being reached as shown by the
“waves” made when drawing the fish. The largest obstacle was the connections
to the FLEX chip on a UP1 board. These connections were meant to be soldered
and nothing else. Any other type of connection will not be reliable.
Appendices:
Code
and Schematics:
3.SEGA
Genesis controller information
4.Top
level schematic:
