main.c File Reference

DSP-1 pseudo-3D: a cube tumbling in 3D, rotated by the coprocessor. More...

#include <snes.h>
#include <snes/dsp1.h>

Macros
#define	CUBE_DIST   400
	Distance from the camera to the cube's centre, along the DSP-1's depth axis. Empirically characterised on luna (DSP-1B): with azs=0x4000 the projection looks along +Y — X is across, Z is up. Rotated corners span ±~139 (80·√3), so 400 keeps every corner in front of the eye.
#define	VIEW_AZS   0x4000
	Screen-plane zenith angle: 0x4000 (90°) = horizontal view, +Y is the depth axis. The all-zero setup is degenerate (every point projects to the origin) — this angle is what makes the projection live.
#define	VIEW_LES   256
#define	VIEW_LFE   96
	dsp1SetCamera FOV knobs, tuned empirically on luna. The effective focal length is close to VIEW_LFE + VIEW_LES (projected offset ≈ (lfe+les)·x/y): 96+256 spreads the corners ±~92 px at CUBE_DIST 400 — filling the 224-line screen without clipping at the nearest swing.

Functions
int	main (void)

Variables
static const s16	cube [8][3]
static const u8	dot_pal [4] = { 0x00, 0x00, 0xFF, 0x7F }
static const u8	dot_tile [32]
volatile u16	dsp1_ok = 0
	1 when the DSP-1 answered the known-answer probe — parked in WRAM so the luna test manifest can assert it (coproc_dsp1.toml).
static const Dsp1Camera	view
	The fixed camera: at the origin, looking along +Y.

Detailed Description

DSP-1 pseudo-3D: a cube tumbling in 3D, rotated by the coprocessor.

Each frame the DSP-1 builds a rotation matrix (dsp1Attitude), transforms the cube's 8 corners through it (dsp1Objective), and projects each corner onto the screen with true hardware perspective (dsp1Project, set up once by dsp1SetCamera). The corners are drawn as 8 sprites — all the 3D math, including the perspective divide, runs on the NEC uPD77C25, not the 65816.

SNES Concepts

• DSP-1 coprocessor command interface (matrix + vector transform)
• Fixed-point 3D rotation offloaded from the CPU
• Hardware perspective projection (Parameter -> Project pipeline)
• dsp1IsPresent() known-answer probe before relying on the chip

What to Observe

• A cube of 8 dots rotating smoothly about two axes
• Perspective: corners swinging toward the camera drift outward (closer = bigger separation), the far face contracts — no longer a flat tumble

Modules Used

console, dma, sprite, dsp1

Warning

Needs the DSP-1 firmware in luna (dsp1b.rom) — see the README.

See also

snes/dsp1.h, .claude/notes/tech/dsp1_reference.md

Macro Definition Documentation

CUBE_DIST

#define CUBE_DIST   400

Distance from the camera to the cube's centre, along the DSP-1's depth axis. Empirically characterised on luna (DSP-1B): with azs=0x4000 the projection looks along +Y — X is across, Z is up. Rotated corners span ±~139 (80·√3), so 400 keeps every corner in front of the eye.

VIEW_AZS

#define VIEW_AZS   0x4000

Screen-plane zenith angle: 0x4000 (90°) = horizontal view, +Y is the depth axis. The all-zero setup is degenerate (every point projects to the origin) — this angle is what makes the projection live.

VIEW_LES

#define VIEW_LES   256

VIEW_LFE

#define VIEW_LFE   96

dsp1SetCamera FOV knobs, tuned empirically on luna. The effective focal length is close to VIEW_LFE + VIEW_LES (projected offset ≈ (lfe+les)·x/y): 96+256 spreads the corners ±~92 px at CUBE_DIST 400 — filling the 224-line screen without clipping at the nearest swing.

Function Documentation

main()

int main

(

void

)

Variable Documentation

cube

const s16 cube[8][3]

static

Initial value:

                      = {
    {-80,-80,-80}, { 80,-80,-80}, { 80, 80,-80}, {-80, 80,-80},
    {-80,-80, 80}, { 80,-80, 80}, { 80, 80, 80}, {-80, 80, 80},
}

The cube's 8 corners in model space (DSP-1 integer coordinates).

dot_pal

const u8 dot_pal[4] = { 0x00, 0x00, 0xFF, 0x7F }

static

Two colours: index 0 transparent, index 1 white ($7FFF).

dot_tile

const u8 dot_tile[32]

static

Initial value:

                         = {
    0xFF,0x00, 0xFF,0x00, 0xFF,0x00, 0xFF,0x00,
    0xFF,0x00, 0xFF,0x00, 0xFF,0x00, 0xFF,0x00,
    0,0,0,0,0,0,0,0, 0,0,0,0,0,0,0,0
}

8x8 4bpp tile, colour index 1 everywhere. In the SNES 4bpp layout planes 0/1 interleave per row, so plane 0 all-set is the ODD bytes 0,2,…,14.

dsp1_ok

volatile u16 dsp1_ok = 0

1 when the DSP-1 answered the known-answer probe — parked in WRAM so the luna test manifest can assert it (coproc_dsp1.toml).

view

const Dsp1Camera view

static

Initial value:

                             = {
    .x = 0, .y = 0, .z = 0,
    .lfe = 96 , .les = 256 ,
    .aas = 0, .azs = 0x4000 ,
}

The fixed camera: at the origin, looking along +Y.