Xmas progress!

Not surprisingly it's been a busy run-in to Xmas with work and home life, though I have done more on Namco Classics than my lack of blog posts would suggest. In fact, I've been quite pleased with my progress given the relative lack of time to work on it.

To continue where the last post left off, I've sorted the interrupt issue. That was due to me not responding with VPAn properly - interestingly that signal was absent on the TG68K core I used many years ago for the beginnings of my Neo Geo implementation. The software seems to be running properly now as far as I can ascertain from the far-from-complete video implementation.

Next step was to get the fx68k core executing code from SDRAM. That involved studying a bunch of different cores to find an SDRAM controller that was relatively 'new' and also suited my circumstances. Turns out the core written by Sorgelig is used in several different cores, and modified as required. After a false start using the Irem92 version of the core (see below), I finally settled on the version used in the SEGA Genesis core. FTR it has 3 channels, though I'm only using 1 atm.

Before I can use the SDRAM core however, I need to be able to download to the SDRAM. For this I found the Irem92 rom_loader module, which uses some magic in the .mra file to download data to both SDRAM and BRAM memory blocks. This was perfect for Namco Classics as I am still loading a subset of the graphics ROM into BRAM, although I soon discovered that I'd need to switch the SDRAM core to that of the Genesis core. Fortunately the rom_loader didn't require any changes.

Finally I was greeted with the SELF TEST screen that I had only seen on the simulator...

68K code running from SDRAM!

I decided to look at the dipswitches next, so I could get the game into the self-test menu. Quite straightforward with the MiSTer framework, so then I started looking at the inputs to the core. This was a little more confusing as the documentation is quite terse on this topic, and took some 'reverse-engineering' of another core to deduce how that actually works. Eventually I could navigate the menu and get into the SWITCH TEST screen.

SELF TEST (inputs) screen (MiSTer)

That just about completes the interfacing with the MiSTer framework, at least until I want to get more into the advanced graphics and sound options.

So back to completing the YGV608 implementation. It doesn't take long for the game to switch into an unimplemented graphics mode. The main title screen runs in 256-colour mode, so that was next. At the end of the day, all that was required was a few more lines of Verilog in the Pattern Generator module and it was displaying correctly!

Title screen - 256 colour mode (MiSTer)

And then the very next screen in attract mode switches to another unimplemented graphics mode... this time 16x16-pixel tiles instead of 8x8-pixel tiles. This is currently WIP, but I at least now see something resembling the proper graphics:

16x16-pixel tile mode (Verilator)

So far the new graphics modes have been trivial to implement, but I'm expecting it to get more complex before too long. Scrolling and paging in particular, and that's not even thinking about rotating and scaling (which the NAMCO intro screen uses!) But soon it may be time to implement the sprite layer!