Here's a work-in-progress port of the 6809E Williams Defender sources from the HistoricalSource repo on github https://github.com/Historicalsource/Defender, to the Atari ST, running at 50Hz and requiring at least 1MB RAM.
The algorithms and game play are by Eugene Jarvis, Sam Dicker, et al.. If it feels like Defender, then that's because of them. If it doesn't, then that's because of me.
Work-In-Progress. Currently implemented bad guys are Landers, Mutants, and UFOs. At the end of a game, the game restarts. No attract mode or high-score table yet.
Keys are:
D/C Up/Down
S Smart Bomb
F Hyperspace
M Thrust
L Fire
SPACE Reverse
Supporting DMA samples on STEs with 2MB+ of RAM, or YM2149 samples on STEs and STs with 1MB RAM. STEs with DMA sound will have much less chop when the screen gets busy.
Most of the STE samples are 12.5kHz. A few, where I could hear a difference, are 25kHz, but not all as that blew beyond 2MB.
Initial classic joystick support is in, supporting joystick 1 up/down/left/right/fire.