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README.md

OKI MSM6295

Summary

4 voice Dialogic ADPCM
- total accessible memory: 256 KByte
Clock divider via SS pin

Source code

msm6295.hpp: Base header
- msm6295.cpp: Source emulation core

Dependencies

vox.hpp: Dialogic ADPCM decoder header
- vox.cpp: Dialogic ADPCM decoder source

Description

It is 4 channel ADPCM playback chip from OKI semiconductor. It was becomes de facto standard for ADPCM playback in arcade machine, due to cost performance.

The chip itself is pretty barebone: there is no "register" in chip. It can't control volume and pitch in currently playing channels, only stopable them. And volume is must be determined at playback start command.

Command format

Playback command (2 byte):

Byte Bit      Description
     76543210
0    1xxxxxxx Phrase select (Header stored in ROM)
1    x000---- Play channel 4
     0x00---- Play channel 3
     00x0---- Play channel 2
     000x---- Play channel 1
     ----xxxx Volume
     ----0000 0.0dB
     ----0001 -3.2dB
     ----0010 -6.0dB
     ----0011 -9.2dB
     ----0100 -12.0dB
     ----0101 -14.5dB
     ----0110 -18.0dB
     ----0111 -20.5dB
     ----1000 -24.0dB

Suspend command (1 byte):

Byte Bit      Description
     76543210
0    0x------ Suspend channel 4
     0-x----- Suspend channel 3
     0--x---- Suspend channel 2
     0---x--- Suspend channel 1

Frequency calculation

 if (SS) then
  Frequency = Input clock / 165
 else then
  Frequency = Input clock / 132