One of the areas of the ZX81 I have always wanted to understand better is the way the screen is generated. There's a lot of info available now, thanks to the ROM disassembly and along with Wilf's, and others, work.
So I've decided to write my own text only driver.
Why I here you cry! Well my aim is to develop a driver specifically for games on the ZX81:
- Remove checks for FAST mode and ZX80 compatibility.
- Incompatible with BASIC.
- Allow IY register and System Variable memory to be used.
- Remove need for HALTS embedded in D-FILE ala NOVA.
- Interrupt routines either at FRAME start or end and possibly specific raster line.
- Transitions between to D-FILES.
- Scroll display down or up from top or bottom margin.
- Document what is happening to my satisfaction.