New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Mega Drive: More info about PCM streaming #98

Open

flipacholas opened this issue May 2, 2022 · 0 comments

Labels

addition

Owner

flipacholas commented May 2, 2022

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 added the addition label

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment