main.c File Reference

HiROM memory mapping mode with 64KB bank access. More...

#include <snes.h>
#include <snes/console.h>
#include <snes/dma.h>
#include <snes/input.h>

Macros
#define	FONT_SIZE   (11 * 16)
	Total font data size in bytes (11 characters x 16 bytes per 2bpp tile)
#define	TILE_B   9
#define	TILE_D   6
#define	TILE_E   7
#define	TILE_H   1
#define	TILE_I   2
#define	TILE_L   8
#define	TILE_M   5
#define	TILE_O   4
#define	TILE_PLUS   10
#define	TILE_R   3
#define	TILE_SPACE   0
	Tile index for space (blank tile)
#define	TILEMAP_ADDR   0x0400
	VRAM word address for the BG1 tilemap (32x32 = 2KB)
#define	TILES_ADDR   0x0000
	VRAM word address for the tile character data.

Functions
static void	clear_tilemap (void)
	Clear the entire BG1 tilemap to blank (space) tiles.
int	main (void)
	Main entry point – HiROM mode validation demo.
static void	write_tile (u8 x, u8 y, u8 tile)
	Write a single tile entry to the BG1 tilemap via direct VRAM registers.

Variables
static const u8	font_tiles []
	Inline 2bpp font tile data (11 characters, 16 bytes per tile).
static const u8	init_palette []
	Initial 2-color palette (dark blue background, white text).

Detailed Description

HiROM memory mapping mode with 64KB bank access.

Demonstrates building an OpenSNES ROM in HiROM mode, where each ROM bank provides 64KB of contiguous address space ($0000-$FFFF) instead of LoROM's 32KB ($8000-$FFFF). HiROM is selected by setting USE_HIROM := 1 in the Makefile, which switches the ROM header, memory map, and linker configuration.

HiROM is preferred for games with large contiguous data (streaming tilesets, large lookup tables) because it avoids the 32KB bank boundary that LoROM imposes. The tradeoff is that mirror-region access patterns differ, and some addressing modes behave differently.

This example uses inline 2bpp font tiles (no external assets) and direct VRAM register writes to display text, confirming that the library, ROM header, and memory map are all correctly configured for HiROM operation. Pressing A changes the background color as a simple input validation.

SNES Concepts

• HiROM vs LoROM memory mapping (64KB vs 32KB banks)
• ROM header configuration for HiROM (USE_HIROM flag)
• Mode 0 with 2bpp inline font tiles
• Direct VRAM register writes for tilemap text rendering
• CGRAM palette writes for runtime color changes

What to Observe

• "HIROM MODE" and "+ LIB" text displayed on a dark blue background
• Hold A to change the background color to light blue
• Release A to restore the dark blue background
• If the text appears garbled, the HiROM configuration has an issue

Modules Used

console, dma, input, sprite, background

See also

console.h, dma.h, input.h

Macro Definition Documentation

FONT_SIZE

#define FONT_SIZE   (11 * 16)

Total font data size in bytes (11 characters x 16 bytes per 2bpp tile)

TILE_B

#define TILE_B   9

Tile index for letter B

TILE_D

#define TILE_D   6

Tile index for letter D

TILE_E

#define TILE_E   7

Tile index for letter E

TILE_H

#define TILE_H   1

Tile index for letter H

TILE_I

#define TILE_I   2

Tile index for letter I

TILE_L

#define TILE_L   8

Tile index for letter L

TILE_M

#define TILE_M   5

Tile index for letter M

TILE_O

#define TILE_O   4

Tile index for letter O

TILE_PLUS

#define TILE_PLUS   10

Tile index for plus sign (+)

TILE_R

#define TILE_R   3

Tile index for letter R

TILE_SPACE

#define TILE_SPACE   0

Tile index for space (blank tile)

TILEMAP_ADDR

#define TILEMAP_ADDR   0x0400

VRAM word address for the BG1 tilemap (32x32 = 2KB)

TILES_ADDR

#define TILES_ADDR   0x0000

VRAM word address for the tile character data.

Function Documentation

clear_tilemap()

static void clear_tilemap ( void  )

static

Clear the entire BG1 tilemap to blank (space) tiles.

Writes 1024 tilemap entries (32x32) with tile index 0 (space) and zero attributes. Must be called during force blank or VBlank.

main()

int main

(

void

)

Main entry point – HiROM mode validation demo.

Verifies that the HiROM memory map, ROM header, and library all work correctly by displaying text and responding to input. The display is set up with inline 2bpp font tiles written directly to VRAM registers, proving that code and data addresses resolve properly in HiROM's 64KB-per-bank layout.

Holding the A button changes the backdrop color as a simple demonstration that the library's input system works in HiROM mode.

Returns

0 (never reached – infinite game loop)

< Tile index for letter H

< Tile index for letter I

< Tile index for letter R

< Tile index for letter O

< Tile index for letter M

< Tile index for letter M

< Tile index for letter O

< Tile index for letter D

< Tile index for letter E

< Tile index for plus sign (+)

< Tile index for letter L

< Tile index for letter I

< Tile index for letter B

write_tile()

static void write_tile ( u8  x, u8  y, u8  tile  )

static

Write a single tile entry to the BG1 tilemap via direct VRAM registers.

Sets the VRAM address to the tilemap position (row * 32 + column) and writes the tile index as a 16-bit tilemap entry (low = tile number, high = attributes). VRAM writes only succeed during VBlank or forced blank – calling this during active display will silently fail.

Parameters

x	Column position in the 32-wide tilemap (0-31)
y	Row position in the 32-tall tilemap (0-31)
tile	Tile character index to write

Variable Documentation

font_tiles

const u8 font_tiles[]

static

Inline 2bpp font tile data (11 characters, 16 bytes per tile).

Each 2bpp tile is 8x8 pixels stored as 16 bytes: 8 rows of 2 bytes each (one byte per bitplane). Only 2 colors are used: color 0 (transparent/background) and color 1 (text). This avoids needing an external font asset file – the entire character set is embedded in the C source.

init_palette

const u8 init_palette[]

static

Initial value:

= {
    0x00, 0x28,  
    0xFF, 0x7F,  
}

Initial 2-color palette (dark blue background, white text).

SNES CGRAM stores BGR555 colors as 2 bytes each (little-endian). Color 0 = backdrop (dark blue), Color 1 = text foreground (white).