Memory contention

The time taken to execute an instruction, measured in t-states, depends on the ASIC's behaviour and the kind of memory (ROM / RAM / external RAM) from where the instruction is fetched and from where the instruction is accessing data.

This can be used to not only improve general speed of execution but also for tightly timed effects like border graphics such as those made by BorderTron 3000.

See https://simonowen.com/sam/timings/ and https://simonowen.com/articles/mode1/