vladikcomper/MegaPCM

An advanced DAC driver for the Sega Mega-Drive / Genesis games

Mega PCM 2

Mega PCM 2 is a DAC sound driver for Sega Mega-Drive / Genesis. It offers the highest quality playback possible on the hardware, high sample rate (up to 32 kHz), pitch/volume effects and supports several sample formats (WAVE, raw PCM, compressed DPCM).

Unlike the majority of DAC drivers on the Mega-Drive with the infamous "scratchy" playback many games are known for, Mega PCM 2 outputs cleanest sounding samples on the hardware thanks to its buffering / DMA protection system.

Mega PCM runs primarily on the Z80 CPU and is DAC only. To take full advantage of Sega's sound chip and also use FM and PSG channels, you need to run it alongside the "main" M68K sound driver. Generally, Mega PCM can be integrated with any M68K sound driver. Currently, only SMPS integration is officially provided.

You may also see this demo of crystal-clear PCM playback @ 32 kHz recorded on real hardware.

Features

• High quality crystal-clear PCM playback with DMA protection;
  • Games usually DMA 6-8 Kb of data at most; Mega PCM 2 can survive up to 24 Kb (!) of DMA transfers;
• Volume control and smooth pitch control;
  • 16 volume levels;
  • 256 pitch levels;
• Complex inside, user-friendly outside:
  • Zero-config DMA protection (no extra flags to set and unset, simply don't stop Z80 on DMA's);
  • Native WAVE file support, native PCM format (no custom converters required!);
  • Auto-detects issues with sample formats or configuration on startup;
• Several supported sample formats:
  • WAVE files in 8-bit unsigned PCM format (sample rate can be detected from header);
  • Raw 8-bit unsigned PCM (headless);
  • Raw 4-bit DPCM (headless);
• Playback control, priority settings and SFX support:
  • Pause, Stop and Loop supported for all sample types;
  • Differentiates between "normal" (usually BGM drums) and SFX samples;
  • SFX samples aren't interrupted by BGM drums, they have separate volume and pan settings;
• Tested to the extreme:
  • Z80 portion of Mega PCM is unique in that it's extensively auto-tested in a virtual machine;
  • A special Z80 emulator was created to emulate Mega PCM and carefully test its core and various functions;
  • Tests also verify that all Mega PCM playback loops and branches are cycle-accurate;
• High playback rates:
  • 8-bit PCM playback up to 25.1 kHz with pitch and volume effects;
  • 4-bit DPCM playback up to 20.5 kHz with pitch and volume effects;
  • Turbo mode! 8-bit PCM playback at 32 kHz (without pitch and volume effects);

Installation and Documentation

Installation guides

• Sonic 1 Github Disassembly (AS version)
• Sonic 1 Hivebrain 2005 Disassembly

Documentation

• API Documentation
• Sample table format
• Migrating from MegaPCM 1.x
• Troubleshooting

How-to guides

• How to play SFX samples
• How to play DAC BGM

Examples

• Basic 32 kHz WAVE playback with looping
• DMA Protection testing ROM
• Complete Sonic 1 SMPS integration as a standalone player

Existing implementations

• Sonic 1 Github AS disassembly with Mega PCM 2 pre-installed: https://github.com/vladikcomper/s1disasm-megapcm2
• Unofficial Sonic 2 Clone Driver v2 with Mega PCM 2 integration in Sonic Clean Engine (S.C.E.) by TheBlad768: https://github.com/TheBlad768/Sonic-Clean-Engine-S.C.E.-

Building from source code

Linux

Make sure Wine is installed. Use the following commands to build:

make
make examples

Windows

You need to have GCC, Make and Python3 installed and availabe via PATH. The easiest way to get everything with one command is to use Chocolatey, but you may choose any other option that works for you:

choco install mingw python3 make

Once dependencies are installed, build process is the same as on Unix-like systems:

make
make examples

If you need to invoke make from individual directories however (not root), be sure to use make -f Makefile.win instead (the root Makefile does it automatically).

FreeBSD

Almost the same as Linux, however you need to make sure to use GNU version of Make.

• Install GNU Make; use gmake command instead of make;

Licensing

Mega PCM 2's main source code and its dependencies (src/ and lib-68k/directories) are fully free and open source and are provided under MIT license. See LICENSE file.

Source code for Mega PCM 2 implementation examples (examples/ directory) is also MIT-licensed, however, some included assets and disassembled "SMPS" sound driver may be proprietary and provided for educational purposes only.

Also included in this repo, but not distributed with Mega PCM 2 releases:

• Mega PCM 2's testing suite (see test/ directory):

  • All tests source code and "MegaPCM-Emu" library retain the same MIT license;

  • "Z80VM" library (tests/z80vm) is a custom solution based on a modified z80emu v.1.3.0 (c) by Lin Ke-Fong; the original software comes without a set license.

• For developer's convenience this repo also includes a few binary tools (see toolchain/ directory):

  • asm68k and psylink are (c) by S.N. Systems Software Limited and come with propriatary license, but are considered abandonware;

  • sjasmplus is a free and open source Z80 assembler available under BSD-3-Clause license;

  • convsym, cbundle and others are written by me and are availabe under permissive MIT License.