Aaendi

Why do you need to move it to a RAM buffer before uploading it to VRAM?

Do you consider the DSP-ADPCM from Nintendo's more recent systems, a fake ADPCM, since it has a lot in common with SNES BRR? DSP (File Format) - Retro Modding Wiki (metroid2002.com)

I meant to say ADPCM, not ADPCM-A. That was a typo. Anyway, I got the wave to brr code down to 2 seconds by using the 4-bit PCM mode (filter 0, range 12). It actually sounds pretty good with the dual saw wave I am using it for, just slightly buzzier than using variable ranges and filters.

How many colors are in that demo? It looks way more than just 16 colors per tile. Is that using a lot of dithering?

BRR is another name for the ADPCM-A sample format the SNES uses. You can find information here: https://wiki.superfamicom.org/bit-rate-reduction-(brr) Doing a full software conversion from wave to brr that makes use of all it's features is pretty processor intense, but there is a 4-bit PCM mode that simplifies it a lot, but is slightly noisier. The SPC700 also has it's own little CPU inside of it, but isn't as fast as the main CPU, but it can run it's own programs while the main CPU is busy. I'm attempting to do an additive synth on the SPC700.

You can place sprites behind or in front of the background in regular mode 7. EXTBG lets sprites go in-between different parts of the background. Plus, if you have 2 transparent layers (mode 7 and sprites), it doesn't matter which layer is in front of which because they both look the same.

I got my software synth code down to just 3 second to draw a 16384 sample long BRR sample. I think this as fast as I can get under the restrictions I placed on it, such as only using 8-bit precision and only using filter 0 and filter 1. The only way to make this even faster is if I restrict it to just using filter 0, and give every block the same range settings, so it acts like a 4-bit PCM. (Or make the 65816 do it, but this would be a lot easier.)

Oh, you're talking about THAT type of sample. A sample can mean either of 2 things. The entire sound, or just one specific point in the wave that makes up the sound.

I guess if you're able to get the timing correct.

Blargg was able to get 16-bit stereo PCM at 32000kHz, which means that it can update 128000 bytes per second. However, that keeps the 65816 busy the entire frame, so it's not practical during gameplay. A more reasonable approach would be to HDMA 4 bytes per scanline, which would theoretically be able to use up to 4*224*60 = 53,760 bytes per second, if the spc700 is in a timed loop that is 65 cycles per loop. However, the spc700 uses a stupid ceramic resonator that isn't synced up with anything else in the system, so if you are doing 4 bytes per scanline you would need to sync it up every several lines in order for it to work, in case of drifting, so you would loop through several scanlines with 65 cycles per loop, then wait for a "sync pulse" so it can resync itself every several lines.

I got it down to 5.5 seconds and there are still a couple more optimizations I can do.

It seems to be more of a problem on my desktop computer than my laptop computer for some reason. The biggest issue right now is how long it takes the SPC to synthesize BRR samples. Luckily I was able to get it down to 6 seconds for 16384 samples (9kB). Originally it was over 10 seconds. I got it down by using a bunch of lookup tables, unrolled loops, self-modifying code, etc.

From looking at the screenshot, I think I can tell what Konami was trying to do. I think the game is trying to remove sprites that are hiding behind other sprites. If the fireballs were shaped like squares, you wouldn't be noticing sprites in the back disappearing, only the sprites in the front.

The torso and head are on a background layer. I'm guessing each of the fire balls that make up his arms are 48x48 and use 9 16x16 plus 2 hands that are 64x32 so that means that his arms already take up to 88 sprites.

I think the game is surpassing 128 sprites too, since I can see individual 16x16 sprites disappearing, and it looks like Konami randomized it too.