Is it a must a simple game like space invader to use timer?
Can I use indefinite loop, and then call subroutine to draw, to detect collision, to check key in every cycle / loop?
It might be slow if without timer, to handle manually, but I haven't put them into practice. Still not decisive whether to create space invader first, or continue studying disassembler project....
Thank you @narf03 and @iammyself for sharing your experience, and thanks @flashang for the links (The Galaxy shooter is not mobile friendly :=).
How difficult it is to create a game like this?