I've heard a beta release (on the Neo Geo is imminent!?!)

Some significant, albeit unexpected progress since last post!

As I mentioned, I've been looking at sound support on the Neo Geo. I'd searched for demo code and downloaded a few, before deciding on one such example. However it had a complicated build process involving lua (whatever the hell that is) and it was broken.

Then I stumbled upon Blastar's NGFX SoundBuilder. It's been a while since I was properly impressed by a piece of software, but this is downright awesome! It has a GUI that allows you to add samples to your project, assign channels and specify looping, and then click on a button and it will generate not only the sound sample ROM, but also the driver ROM in its entirety!

Writing Z80 sound drivers for the Neo Geo has never been easier!

Playing sounds using the driver is trivial; write a single byte (ordinal) to the sound register and it starts to play. A few extra commands to mute and stop looping etc, but that's really all there is to it as long as you have assigned samples to the right channels!

As a result, given that jotd has sampled most of the sounds already, all I needed to do was convert them to 18.5kHz, run NGFX SoundBuilder, add a handful of 68K instructions, and most of the sound is playing on the Neo Geo! I'm still shaking my head at how easy it was. What it all means is that the beta release will probably have full sound (just one sound missing, and a few to test in-game)!

[An aside, I had to produce one of the samples myself - the ground-based object explosion. The complication with ripping it from MAME was the fact that it was mixed with the background tune of the Solvalou. Having RE'd the game - including a lot of the sound ROM - I was able to patch the ROM to remove the tune and, while I was at it, the sound of the bomb that would immediately precede the explosion. Booting up Xevious with the option to record sound to WAV, I waited for the first ground object to bomb, bombed it, and immediately quit MAME.

Loading the WAV into Audacity, it was easy to spot the explosion near the end of the file. I clipped it, saved the clip, and converted it using sox to 18.5kHz mono for the Neo Geo. Trivial!]

Currently I'm just missing the start-up tune -which jotd has sampled and included in his Amiga port - so I'm just waiting for him to push it to his repository. Incidentally, he has just released a preview version of the Amiga port on the EAB site!

Whilst I've been adding sound however, I haven't even looked for the last (known) gameplay bug. I knew it wasn't related to the Neo Geo code, but it was nice to get confirmation from jotd when he saw the same issue on the Amiga port!

So right now, I think I'm just one .WAV file and one bugfix away from a full beta release with sound!

UPDATE: I've added the main theme, so I think all the sounds are there! I did discover that one of the channels isn't available on the NGCD, so I will have to tweak the channel assignment. But at the end of the day, I don't think it'll make any functional difference.

The main theme was a bit of a kludge in the end. The problem is that the original code calls 'play main theme' continually for about 3 seconds (somewhat bizarrely, that's only about halfway through the theme playing)?!? At the same time, it's continually calling 'play solvalou sound'. While the theme is playing, that takes precedence, but as soon as the sample is finished the solvalou sound kicks in. All that is done in the sound driver... with no control or visibility in the main program.

That presents a problem for the transcode, and doubly so on the Neo Geo using the NGFX SoundBuilder, as there is no way of knowing when the main theme has finished. jotd has the same issue on the Amiga port.

The solution - first suggested by jotd - is to start a counter when the main theme is playing, and essentially time it. It's possible because the 'play solvalou sound' call runs all the way through the theme at a nicely predictable 60Hz. It seems to work well!

The only other 'kludge' I needed for sound was to add osd_sound_mute and osd_sound_unmute calls to the main code around the attract mode. This is because the arcade sound ROM actually checks the attract_mode_stage variable itself and handles muting there.

Only one known gameplay bug to go... although jotd did question something he saw in the Amiga port today...