Medieval Mayhem for the Atari VCS

Last update: updated links to AtariAge.

During Christmas of 2005 I played Warlords with my nephews and their friends. It's one of the few 4 player games made for the Atari VCS(also known as the 2600). In seeing the graphics, their friends were initially unimpressed with the Atari as they'd grown up with Playstations and Xboxes. They were quickly won over by the game play and we had a blast.

Warlords

I'd long wanted to write a game for the Atari VCS and decided to do a remake of Warlords that had more of the features found in the original arcade game. Features I wished to add were multiple fireballs, a greater range of fireball movement, and the launch dragon. I also wanted to add an options menu - back then you'd look up game variations in a matrix in the game manual to figure out the game number you wished to play. When Warlords was written 4KB was the norm and a menu would not have been feasible. Medieval Mayhem ended up utilizing 32KB, 6KB of which was the menu.

Medieval Mayhem

Main Menu	Launch Dragon
Multiple Fireballs	Round Winner

Programming for the Atari VCS is a lot different than anything I've ever programmed for before. The biggest difference is there's no video memory - the CPU draws the screen in real time. It even controls the TV sync signals required for a stable picture. Other obstacles to overcome are 4KB of ROM space, limited graphic capabilities and just 128 bytes of RAM. Not megabytes, not kilobytes, just bytes.

The Atari does have a graphics chip, known as TIA, but unlike modern systems with video RAM, TIA only has registers which control the drawing of a single scanline. If the CPU doesn't change the TIA registers then each and every scanline would show the same thing. Less than half the CPU's time can be utilized for game logic because it's so busy updating TIA with what to display.

The Atari can only address 4KB of ROM - so I'm sure you're wondering how Medieval Mayhem could be a 32KB game. This is accomplished by special hardware added into the cartridge that supports bankswitching. The 32KB of ROM is split up into 8 4KB banks. When the game code needs to access something in a differant bank it accesses a trigger location which tells the cartridge to select a different bank for the Atari to see. This is similiar to how you turn pages to view a different part of a book.

While the Atari was colorful for it's time(128 different colors vs 15 for the Colecovision and 16 for the Intellivision), it only supported 2 sprites, 2 missiles, a ball and the very pixelated playfield graphics. In Warlords, the sprites were used for the player's shields, the missiles for the kings, the ball for the fireball and the playfield for the castle walls. The 2 sprites and 2 missiles are reused while the screen is drawn in order to draw 4 kings and 4 shields. Medieval Mayhem draws the kings using the playfield graphics and uses the SCORE MODE of the Atari to color the kings differently than the rest of the castle. This frees up the 2 missiles to be used as fireball 2 and 3. The 2 sprites are used an additional time in the center section of the screen to draw the dragon.

Developement History Screen Shots

Main Menu	Game Screen

As good as I am at programming, I'm not that good at creating music or art. David Vazquez did the dragon, knight and king graphics and Erik Ehrling coded music, Druid Chip.

You can download the ROMs below to play on your computer via an emulator such as Stella, but be warned that the mouse makes a poor substitue for paddles. Medieval Mayhem can be purchased for play on a real Atari for $25 at AtariAge.com.

© 2007 Darrell Spice Jr.