smsgg-core

Sega Master System / Game Gear / SG-1000 emulation core.

The Sega Master System contains the following components:

Z80 CPU clocked at 3.58 MHz
VDP (video display processor) that is derived from the Texas Instruments TMS9918 but sports an additional advanced graphics mode (which nearly every game on the console uses)
- Renders at 256x192
- Supports 6-bit RGB color with up to 32 colors onscreen simultaneously
- Contains a single background layer
- Supports up to 64 sprites per frame and up to 8 sprites per scanline, with sprites being 8x8 pixels
SN76489, a PSG (programmable sound generator)
- Contains 3 square wave generators and a noise generator
8KB of working RAM
16KB of VRAM
32 bytes of CRAM (color RAM for storing palettes)
Support for an optional FM sound unit expansion, which adds a YM2413 FM synthesis chip

The Game Gear is nearly identical to the Master System hardware-wise, with a few key differences:

The VDP still renders 256x192 frames, but only the center 160x144 pixels are displayed
The VDP color format is changed from 6-bit RGB to 12-bit RGB, and color RAM is doubled in size to accommodate this
The Start/Pause button flips a bit in a register instead of generating an NMI
There is a new stereo sound control register that enables hard panning each of the 4 audio channels

SG-1000 is the Master System's predecessor, and it differs in the following ways:

1KB of working RAM instead of 8KB
Video processor is an actual TMS9918A, not Sega's customized version used in SMS/GG (and a later version in Genesis)
SN76489's noise channel has slightly different behavior in white noise mode, since it's a stock SN76489 rather than a Sega-customized chip
Cartridge memory mapping is much simpler; no games used memory-banking mappers

This crate contains code for: