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Published 20 hours ago • verified publisher icon flipacholas

Mega Drive: More info about PCM streaming

Open flipacholas opened this issue 2 years ago • 0 comments

From https://twitter.com/grievre_ebooks/status/1521084538729811968 by @grievre_ebooks

@Flipacholas I have an extra piece of info for your Mega Drive article: It was very difficult to smoothly play back PCM samples because the video DMA operations would block the main bus, and most games halt the Z80 during that to avoid a crash-inducing bug.

This means that most PCM sample playback has noticible flat spots during the time that the video DMA was occurring, because the 2612 could only accept samples one at a time, in real time. However, you could avoid this, and a small minority of games did.

If you look at games by Treasure (e.g. Dynamite Headdy) you will find they have much cleaner PCM than even first-party games like Sonic 3. They managed to figure out how to buffer PCM samples in Z80 RAM so they could keep playing back while the main bus was blocked.

flipacholas avatar May 02 '22 20:05 flipacholas