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Toorum's Quest II – game running on Arduino ATmega328P Microcontroller
Made on an ATmega328P microcontroller (MCU) which has only 2 kilobytes of RAM and 32 kilobytes of program memory.
"Everything, the NTSC video signal generation, sound synthesis, music playroutine and game logic is running on the MCU, so many things had to be hand-optimized in assembler language. Only a single additional IC, the AD725 is needed in addition to the ATmega328P."
The video:
https://www.youtube.com/watch?v=sLvgW_zb6bQ
How it's done:
http://www.gammon.com.au/forum/?id=12623