The Japanese home computer market of the 1980s was its own ecosystem — sharper graphics, richer sound, and a software library that rarely left the archipelago. Two of those machines are now launchable in the sigilOS RetroPie layer: the NEC PC-88 and the Sharp X68000. Both were already in the repo as bus skeletons; both landed as fully launchable cores in today's session. The launchable count holds at 40 — a launcher de-duplication fix landed alongside these cores correcting a stale slot.
System #40 — NEC PC-8800 (PC-88)
The PC-88 series dominated the Japanese home computer market from 1981 through the late 1980s. Its CPU is the Z80A at 4 MHz — the same Z80 variant that powered the MSX, ZX Spectrum, and CP/M machines of the era. sigilOS already has a Z80 core from the MSX and Master System implementations; the PC-88 core in cores/pc88.sg uses it directly.
The framebuffer: 3-plane 640×200
The PC-88's graphics mode is its defining characteristic: a three-plane 640×200 framebuffer. Each pixel is represented by one bit in each of three planes — R, G, and B — stored at separate base addresses in video RAM. To decode a pixel, the emulator reads the corresponding bit from each plane and combines them:
r = (plane_r[byte] >> bit) & 1
g = (plane_g[byte] >> bit) & 1
b = (plane_b[byte] >> bit) & 1
argb = 0xFF000000 | (r * 0xFF << 16) | (g * 0xFF << 8) | (b * 0xFF)This gives 8 colors (the 3-bit RGB combinations). The decode runs per-pixel across all 640×200 = 128,000 positions into a standard ARGB32 framebuffer for the compositor. No palette table needed — the 8 colors are fully determined by the 3 bit values.
The bus
| Region | Address | Size |
|---|---|---|
| ROM (BIOS/BASIC) | 0x0000 | 32 KB |
| RAM | 0x8000 | 32 KB |
| VRAM — plane R | video base | 8 KB each |
| VRAM — plane G | video base + 0x2000 | 8 KB |
| VRAM — plane B | video base + 0x4000 | 8 KB |
| I/O port $30 | — | Display mode + memory bank control |
What's wired
- Z80A bus — ROM + RAM + 3-plane VRAM + I/O port $30
- Framebuffer decode — 640×200 × 3-plane → ARGB32
- EL0 app — loads
/roms/game.pc88(32 KB cap, SECURE capability) - Core ABI + launcher — standard RetroPie entry; PARITY.md marks LAUNCHABLE
Sharp X68000
The Sharp X68000, launched in 1987, was a home computer aimed squarely at arcade-quality gaming. Its CPU is the Motorola MC68000 at 10 MHz — the same processor as CPS-1, CPS-2, and the original Macintosh. But where those systems drove it with specialized arcade or desktop hardware, the X68000 gave it a sophisticated graphics chip (the CRTC + GVRAM) capable of modes that weren't common on home computers until years later.
GVRAM: 4bpp with indexed palette
The X68000's primary graphics mode uses a 4-bit-per-pixel indexed framebuffer (GVRAM) at 512×512 logical resolution, typically displayed as 512×256 or 256×256. Each byte of GVRAM encodes two pixels: the high nibble is the left pixel's palette index (0–15), the low nibble is the right pixel's. A 16-entry palette in the CRTC register block stores the RGB555 color for each index:
for each byte in gvram:
left_idx = (byte >> 4) & 0xF
right_idx = byte & 0xF
left_rgb = palette[left_idx] # RGB555
right_rgb = palette[right_idx]RGB555 to ARGB32 conversion: R = bits 10–14 (× 8), G = bits 5–9 (× 8), B = bits 0–4 (× 8). The × 8 scaling maps 5-bit [0..31] into 8-bit [0..248] — close enough for display without fractional math.
The bus
| Region | Address | Size |
|---|---|---|
| ROM (BIOS/IOCS) | 0x000000 | 1 MB |
| RAM | 0x080000 | 2 MB |
| GVRAM | 0xC00000 | 512 KB |
| CRTC palette | 0xE82200 | 32 bytes (16 × RGB555) |
| I/O (DMAC/MFP/OPM) | 0xE80000+ | mapped stubs |
What's wired
- MC68000 bus — ROM + RAM + GVRAM + CRTC palette regs
- GVRAM decode — 4bpp indexed, 512×256 → ARGB32 via palette
- Palette — 16-entry RGB555 → ARGB32 with ×8 channel scale
- EL0 app — loads
/roms/game.x68(3 MB cap, SECURE capability) - Core ABI + launcher — standard RetroPie entry; PARITY.md marks LAUNCHABLE
Comparing the two
| PC-88 | X68000 | |
|---|---|---|
| CPU | Z80A @ 4 MHz | MC68000 @ 10 MHz |
| Resolution | 640×200 | 512×256 (typical) |
| Color depth | 3-plane RGB (8 colors) | 4bpp indexed (16 colors, 65536-color palette space) |
| Graphics mode | Planar bitfield | Packed nibble + palette lookup |
| Era | 1981–late 1980s | 1987–mid 1990s |
| Known for | RPGs, strategy games, early Japanese PC gaming | Arcade ports, Gradius, Castlevania |
Both use CPUs already present in the sigilOS RetroPie layer — the Z80 (MSX, SMS, Game Boy) and the 68000 (CPS-1, CPS-2, CPS-3, MegaDrive). The new work in both cores is the graphics decode: the PC-88's 3-plane bitfield and the X68000's 4bpp nibble-plus-palette. Neither required changes to the existing CPU implementations.
40 launchable systems
The RetroPie layer stands at 40 launchable systems. Every core runs as a capability-isolated EL0 process — ROM and disk images are loaded with size-capped SECURE capability tokens. The host OS and every other process are structurally unreachable from inside a running emulator core.