Screenshot

Port of krom (Peter Lemon)'s RedSpace9BitHDMA demo (PeterLemon/SNES, PPU/HDMA/RedSpace9BitHDMA). The SNES has 5 bits per color channel; this classic trick fakes more: HDMA channel 0 rewrites the backdrop color every scanline while channel 1 rewrites INIDISP master brightness (16 levels) on the same line. Red level × brightness, plus per-line jitter in both of krom's tables, dithers the 224-line ramp into far more perceptual steps than 32 — "9-bit" color. Compare with hdma_indirect_gradient (pure 5-bit ramp): this one has visibly finer banding.

There is no BG at all (TM=0) — the whole image is the backdrop — and the demo never calls setScreenOn(): INIDISP is owned by the HDMA stream.

Measured parity: 0 differing pixels against krom's ROM (both rendered in luna v1.9.0) — the tables are his exact bytes, extracted verbatim.

SNES Concepts

Two HDMA channels cooperating on one visual (color + brightness)
HDMA into INIDISP ($2100): per-scanline master brightness
HDMA_MODE_2REG_2X into CGADD: [addr16][data16] = one palette write/line
Backdrop-only rendering; screen-on via HDMA instead of setScreenOn()

Register fidelity vs the original

Register	krom	this port
DMAP0/BBAD0	%011 / $21	same (hdmaSetup(ch0, HDMA_MODE_2REG_2X, HDMA_DEST_CGADD, …))
DMAP1/BBAD1	%000 / $00	same (hdmaSetup(ch1, HDMA_MODE_1REG, HDMA_DEST_INIDISP, …))
HDMAEN	%11	same
TM	0	same (setMainScreen(0))
Tables	224+224 entries	byte-verbatim (res/*.bin)

How to Build

cd examples/color/gradient_9bit && make

Modules Used

console, dma, hdma