Tuesday 26 December 2017

A day of squashing bugs

Part way through today I was feeling that I hadn't really achieved very much, but then as I started thinking about it, and making a list, I realised that I have done more than I first thought.

The list of bugs squashed since the 24th now includes:

24DEC17 - 800x600 video modes work
24DEC17 - Joystick input not working
24DEC17 - CPU bug fixed (Boulder Mark etc runs fine)
24DEC17 - b0 command in UART monitor stops CPU on BRK instruction
25DEC17 - Fix $DC00 always reading as zeros
26DEC17 - Fix sprite fine horizontal placement problem
26DEC17 - PDM/Sigma-Delta audio output working (audio was broken)
26DEC17 - Kickstart looks for file "NTSC", if not present, switches to PAL
26DEC17 - CIA clock speed is always 1MHz, except in C128 2MHz mode.
26DEC17 - Fix CIA clock halving bug
26DEC17 - $D016 smooth scroll in 320H mode fixed
26DEC17 - CIA is 1MHz even in 2MHz mode (turns out to be the correct behaviour)
26DEC17 - NumLock on PS/2 / USB keyboard is now "joystick lock" (WASD+shift, cursors+space)

This has largely been a process of getting all the stuff working again that has broken during the change of video mode, and the incorporation of bitplanes and other missing features.

While there are still a lot of fixes to be made, it is now back to the point where a number of games load and run just fine, and with the improved joystick emulation, these are both easier and more fun to test.  This of course necessitated some play-testing.  There are still quite obvious display glitches, but many of these are due to a relatively few bugs, including some raster position bugs that are on the list to work through.

For now, I will leave you with a set of images following the process of startup, to playing a game: Kickstart loads C65 mode, from there to C64 mode, mount a disk image from SD card, load the menu from the disk, play the game.  Of course, this will all be much more streamlined for final release, but it is already quite usable.  My 7 year old son is just about on top of how to load and play Ghosts and Goblins, which is his current favourite.


  1. Congratulation! I try to follow the commits and at least view the changes if it makes sense for my beginner VHDL knowledge, but I can even hardly keep up with this rate, so really nice work :D :D