main.c File Reference

Mode 3 full-color (256-color, 8bpp) background with assembly DMA loader. More...

#include <snes.h>

Functions
void	loadGraphics (void)
	Assembly DMA loader for large 8bpp tile data (defined in data.asm)
int	main (void)
	Entry point – load 256-color tileset via ASM and display Mode 3 image.

Detailed Description

Mode 3 full-color (256-color, 8bpp) background with assembly DMA loader.

Displays a 256-color background using Mode 3, the highest color-depth tiled mode on the SNES. Each tile is 64 bytes (8 bitplanes), so even a modest tileset exceeds 32 KB and cannot fit in a single ROM bank. The tile data is placed in SUPERFREE sections by the linker, which may assign them to bank $01 or higher. A hand-written assembly DMA loader (loadGraphics in data.asm) uses the linker-provided bank byte (:label) to transfer tile data, tilemap, and palette to VRAM/CGRAM correctly regardless of which bank the data lands in.

This is a direct port of the PVSnesLib "Mode3" example.

SNES Concepts

• Mode 3: single BG layer at 8bpp (256 colors from a 256-entry CGRAM palette)
• 8bpp tile format: 64 bytes per tile (8 interleaved bitplanes)
• Bank overflow: >32 KB tile data requires SUPERFREE sections + assembly DMA with :label bank byte
• Assembly DMA loader pattern: sets $4304 (bank), $4302 (address), $4305 (size) per transfer
• VRAM layout: tiles at $0000 (large), tilemap at $6000

What to Observe

• A single full-screen image with up to 256 unique colors
• Richer color gradients and detail compared to Mode 1 (16 colors)
• Static display with no scrolling

Modules Used

console, dma, background

See also

background.h, dma.h, video.h

Function Documentation

loadGraphics()

void loadGraphics ( void  )

extern

Assembly DMA loader for large 8bpp tile data (defined in data.asm)

Because Mode 3 tile data (64 bytes per 8x8 tile) typically exceeds 32KB, it cannot fit in a single ROM bank. The linker places SUPERFREE sections in whatever bank has space, potentially bank $01 or higher. C code cannot access these banks directly (lda.l $0000,x always reads bank $00), so an assembly routine uses the linker-provided bank byte (:label) to set the DMA source bank register ($4304) correctly for each transfer.

main()

int main

(

void

)

Entry point – load 256-color tileset via ASM and display Mode 3 image.

Forces blank, calls the assembly DMA loader to transfer 8bpp tile data, tilemap, and 256-color palette into VRAM/CGRAM with correct bank bytes, then configures Mode 3 and turns on the screen. Mode 3 supports a single BG layer with 256 colors per tile (8 bitplanes), providing the richest color depth available in any tiled SNES mode. The tradeoff is that only one BG layer is available (plus a second 4-color direct-color BG that is unused here).

Returns

Never returns (infinite loop).