[exsf0859]

Back in the day, I saw VCS game developers use two techniques:

1) they would start with a working kernel from an existing game, and incrementally modify it to create a new kernel for a new game.

2) they would code 2-dimensionally on large sheets of graph paper, where each cell corresponded to both a 6507 CPU cycle and a portion of the horizontal scan line.

By writing out the instructions this way, they could visually check that the code would execute at the correct time.