Memory map

The WonderSwan's SoC uses a 20-bit physical memory map, split into three regions with distinct bus widths, timings, and access permissions;

WonderSwan physical memory map

Bus	Address range		Access width	Access speed	Read/Write
Internal	0x00000 0x0FFFF		16-bit	1 cycle	RW
Cartridge	0x10000 0xFFFFF	0x10000 0x1FFFF	8-bit	1(color)/2 cycles (configurable)	RW
		0x20000 0xFFFFF	8/16-bit (configurable)	1/2 cycles (configurable)	R

Internal

The WonderSwan SoC features an unified memory architecture. The CPU, Display and Sound components make use of data stored in a shared RAM in distinct segments of the 12.288 MHz SoC clock. This is in contrast to many other platforms which feature, for example, separate video memory. This allows the CPU to modify video and audio data without worrying about wait states or video timing; however, the video and audio components have location and alignment restrictions for data:

WonderSwan SoC internal memory map

Address	WonderSwan	WonderSwan Color (2BPP mode)	WonderSwan Color (4BPP mode)
0x0000	Interrupt vectors (256 x 4 bytes - far addresses)
0x0400	Free RAM
0x2000	Tile data (bank 0)		Free RAM
0x4000		Tile data (bank 1)	Tile data (bank 0)
0x6000		Free RAM
0x8000			Tile data (bank 1)
0xC000		Free RAM
0xFE00		Color palette
0xFFFF

In addition, some elements can be placed at configurable locations in RAM, but with restrictions:

WonderSwan SoC internal memory layout limitations

Type	Lowest address	Highest address	Alignment
Screen	0x0000	0x3800 0x7800(color)	0x800 (2048) bytes
Sprite table	0x0000	0x3E00 0x7E00(color)	0x200 (512) bytes
Sound wave table	0x0000	0x3FC0	0x40 (64) bytes

Note that an element being present on this map does not mean that the space cannot be utilized for other data. For example, it is common for a WonderSwan game to only reserve sixteen out of the 256 interrupt vectors, reusing the remaining 240 as general RAM space.

Cartridge

The cartridge part of the memory map is fully controlled by the cartridge bus; this is usually subdivided further by a Mapper. There exists a standard layout common to all official mappers:

Standard mapper physical memory map

Address range	Bank
0x10000 0x1FFFF	SRAM (or flashable ROM)
0x20000 0x2FFFF	ROM bank 0
0x30000 0x3FFFF	ROM bank 1
0x40000 0xFFFFF	ROM linear (EX) bank