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Tigerbyte — Tiger Game.com Notes

A from-scratch libretro core for the Tiger Game.com (1997) — Tiger Electronics' cartridge handheld built on a Sharp SM8521, a 200×160 four-level grayscale LCD, and a resistive touchscreen.

The Game.com is barely documented, so most of this wiki is original reverse-engineering — the real problems hit while building the emulator and the solutions that worked. If you're emulating this machine (or just curious how it works), start here.

Using the core

• Building & Setup — build for Windows / Linux / Android, and where the system ROMs go.
• Controls — d-pad and A/B/C/D map to the RetroPad; Menu/Pause/Sound map to Start/Select/L. The touchscreen is a standard pointer device, so a mouse, a phone screen, or a bezel overlay all drive the stylus.

Hardware notes

• The SM8521 CPU — 8-bit core, banked register file, 67 instructions / 23 addressing modes, and the cycle-timing caveat.
• Boot Sequence — internal ROM → signature handshake → clock-stabilization STOP → the interrupt-driven shell.
• Memory & the MMU — the address space and the four paged windows.
• Video: VRAM & the DMA blitter — the column-major framebuffer, the grayscale palette modes, and the hardware sprite blitter.
• Interrupts & Timers — the priority model and the timing sources that drive the kernel.
• Sound — the wavetable channels and the streaming DAC.

How it was built

• Reverse-Engineering with Lockstep — the single most useful technique: validating the CPU instruction-for-instruction against a reference, and how it found real bugs in minutes.