DSP-1 ground: the Super Mario Kart floor — per-scanline Mode 7 matrices streamed by the coprocessor's Raster command.
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| #define | CAM_AZS (0x4000 - 655) |
| | Zenith angle of the view line: 0x4000 is horizontal (horizon at the screen centre); 0x4000 - 655 tilts down 3.6 degrees so the horizon lands 16 lines above centre (line 96) and the ground below fits one 126-line HDMA repeat block.
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| #define | CAM_HEIGHT 80 |
| | Camera height above the ground plane (DSP-1 integer units). Lower = more dramatic near-row magnification; SMK sits low like this.
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| #define | CAM_LES 256 |
| | Viewpoint → screen distance: 256 gives the 50-degree horizontal FOV of a 256-pixel screen, and it is the vertical focal length that turns the tilt into a horizon raster (Vva = -256*tan(tilt)).
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| #define | CAM_LFE 96 |
| | Base point → viewpoint distance; the viewer sits this far behind the camera point along the view line.
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| #define | CH_AB HDMA_CHANNEL_3 |
| #define | CH_CD HDMA_CHANNEL_4 |
| #define | CH_MODE HDMA_CHANNEL_1 |
| | HDMA channels: BGMODE switch, TM switch, M7A/M7B, M7C/M7D. 1-4 like mode7/perspective (0 is the general-DMA channel, 7 the OAM one).
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| #define | CH_TM HDMA_CHANNEL_2 |
| #define | GROUND_MAX 127 |
| | Largest HDMA repeat block (7-bit count). The ground uses one.
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| #define | MOVE_STEP 4 |
| | Forward speed in ground units per frame.
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| #define | TABLE_HDR 6 |
| | Payload offset in a matrix table: [sky count][4 sky bytes][repeat header].
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| #define | TABLE_SIZE (TABLE_HDR + GROUND_MAX * 4 + 1) |
| | One matrix table: sky entry, repeat block of GROUND_MAX rasters, terminator.
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| #define | TURN_STEP 0x0100 |
| | Heading change per frame while turning (16-bit angle, 2^16 = 360).
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| static u8 | back |
| | Table set being filled this frame (the other one is on screen).
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| static Dsp1Camera | cam |
| | The camera: position on the ground plane (x, y wrap with the 1024-unit texture), height, lens, heading (aas: 0 looks up the map, -Y; 0x4000 looks to +X) and tilt. The luna manifest reads x, y and aas.
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| static s16 | cx |
| | Ground point under the imaginary centre (last dsp1SetCamera).
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| static s16 | cy |
| volatile u16 | dsp1_ok = 0 |
| | 1 when the DSP-1 answered the known-answer probe (luna manifest asserts it).
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| static u8 | ground_lines |
| volatile u16 | raster_lines = 0 |
| | Rasters streamed in the last dsp1Raster call (luna manifest asserts it).
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| static u8 | sky_lines |
| | Screen line of the first ground raster and the block length.
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| static FAR u8 | tab_ab [2][(6+127 *4+1)] |
| | Double-buffered M7A/M7B tables: HDMA reads one while the DSP-1 fills the other.
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| static FAR u8 | tab_cd [2][(6+127 *4+1)] |
| | Double-buffered M7C/M7D tables.
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| static u8 | tab_mode [5] |
| | BGMODE table: Mode 3 for the sky lines, then Mode 7 for the rest.
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| static u8 | tab_tm [5] |
| | TM table: BG2 (sky) for the sky lines, then BG1 (ground).
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| static s16 | vof |
| | Geometry from the last dsp1SetCamera: imaginary-centre raster, horizon raster.
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| static s16 | vva |
DSP-1 ground: the Super Mario Kart floor — per-scanline Mode 7 matrices streamed by the coprocessor's Raster command.
mode7/perspective fakes a receding floor with a precomputed M7A/M7D table; this example asks the DSP-1 for the real thing. Each frame the CPU sends the camera (position, height, heading, tilt) with dsp1SetCamera, then dsp1Raster streams one 2x2 matrix per screen line — A, B, C and D, so the floor rotates with the heading for free — straight into two HDMA payloads. The HDMA channels replay them next frame while the CPU already computes the frame after (double buffering). Above the horizon the same HDMA split as mode7/perspective shows a Mode 3 sky.
The three numbers dsp1SetCamera hands back beside the matrices are the whole geometry: Vva says on which raster the horizon sits, Cx/Cy say which ground point is under the screen centre (they go to M7X/M7Y), and the Mode 7 scroll registers just pin that centre to the middle of the screen.
- SNES Concepts
- DSP-1 Raster: open-ended command streaming Mode 7 matrices per raster
- Parameter outputs (Vof, Vva, Cx, Cy) driving M7X/M7Y and the HDMA split
- HDMA_MODE_2REG_2X repeat blocks feeding M7A/M7B and M7C/M7D
- Double-buffered HDMA tables swapped with hdmaSetTable in VBlank
- dsp1Triangle as the movement sin/cos
- What to Observe
- A textured ground plane receding to a horizon under a sky
- D-pad Left/Right turn the camera: the floor rotates in true perspective and the sky pans with the heading (one turn = the 512-px sky map)
- D-pad Up/Down drive forward/backward along the heading
- Modules Used
- console, dma, background, input, mode7, hdma, dsp1
- Warning
- Needs the DSP-1 firmware in luna (dsp1b.rom) — see the README.
- See also
- snes/dsp1.h, docs/tutorials/dsp1.md, examples/mode7/perspective
1.16.1