Some good progress today even though there's not a lot to show for it.
I fixed a couple of bugs (including the stubborn explosion sprite one) that weren't directly related to transcoding the actual Z80 instructions to C. And speaking of the sprite bug; I stared at it a while longer before it struck me that the sprite codes for half the ship explosion were out of range! What that meant was that they had flip X/Y bits set - which I hadn't yet implemented!
The other bug was the 'graphical glitch' on the text way back from Day 1. Today I noticed that it only seemed to occur on the attract screens, and then I noticed it was only on the 'space' character, and always the same glitch. Didn't take long to realise that my text strings were using the wrong character code for space! All fixed now.
I worked through the collision routines for the ship and different objects, such as rockets, ufos, fireballs, and ground-based objects, and finally the landscape. I had to patch the code temporarily to trigger different collisions in demo mode, but everything I can test in the demo seems to work now. I also did a big clean-up of all the C code, removing the ASM code (comments) from routines that are considered complete.
So on to starting a game; implementing coin-up, reading from hardware (dipswitches, coin mechanisms and buttons), more scripts and initialisation code to transcode. I also had to hack a fix for a race condition between my two threads - since I don't actually have a proper, pre-emptive vertical blank interrupt (NMI) routine - but works better now.
Current state of progress is that you can coin up and start a game, but you don't get to see any evidence of the latter as of yet.
Next I'll continue on with getting a game to start, and either moving the ship or finishing off the higher level mechanics of the 1 and 2 player game lifecycle. That'll leave bullets, bombs and their interactions.