I bite the bullet and uploaded the first working version of Atomchess 6502 for Atari VCS/2600.

The port from my x86 version took 3 hours and another 2 hours this morning to debug, the visuals were coded last night in a crazy 3 hours and I'm happy because the vertical synchro generates exact 262 lines.

Still going to test in real hardware, it should work just fine because Stella is a very good emulator.