Monday, 20 January 2014

Space Invaders, Session 1

A start made on Space Invaders. The basic rendering is done and working, and you can't see it here, but the 'march down the screen' bit also works - if you run the app it starts up the top right, goes to the left, down one, goes to the right and so on.

This is the first time I've written cross-chapter code. A TMS1100 is a TMS1000 with the extra 1k ROM bodged on using a Chapter Buffer, Chapter Address and Chapter Subroutine Store, which means that the actual program counter (423) is built up of three numbers - Chapter Address (one bit), Page Address (4 bits) and Program Counter (6 bits), making 2k in total.

I thought this would be annoying to program, but actually it doesn't make much difference. You can't actually set the CB flag (that is copied to CA when you jump/call) , just toggle it, so that's one thing to keep track of but it isn't that much of a problem to do so.

 Note there is very little animation in this game, just moving blocks. But that applies to virtually all Microvision games.