1.6 KiB
Mandel-6502
Work-in-progress Mandelbrot fractal viewer for Atari 8-bit home computers. Mostly an excute to write an integer multiplication routine for the 6502 for practice.
Goals:
- have fun learning 6502 assembly
- make an old machine do something inefficient as efficiently as possible.
- post cool screenshots of low-res fractals
Non-goals:
- maintain anything long-term (but feel free to copy/fork if you want to make major changes!)
Enjoy! I'll probably work on this off and on for the next few weeks until I've got it producing fractals.
-- brion, january 2023
Current state
The 16-bit signed integer multiplication seems to be working, though I need to double-check it some more. It takes two 16-bit inputs and emits one 32-bit output in the zero page, using the Atari OS ROM's floating point registers as workspaces. Inputs are clobbered.
The main loop is a basic add-and-shift, using 16-bit adds which requires flipping the sign of negative inputs (otherwise you'd have to add all those sign-extension bits). Runs in circa 450-750 cycles depending on input (I'll run the exact numbers again later).
The mandelbrot loop is partly sketched out but I have future updates to make on that.
I've also sketched out a 16-bit rounding macro, which is not yet committed.
Deps and build instructions
I'm using ca65 as a macro assembler, and have a Unix-style Makefile for building. Should work fairly easily on Linux and Mac. Might work on "raw' Windows but I use WSL for that.
Currently produces a .xex executable, which can be booted up in common Atari emulators and some i/o devices.