32MB RAM expansion

By replacing the Dreamcast's two 8MB SDRAM chips with larger SDRAM chips, modifying the pin arrangement, and modifying the BIOS, it is possible to install 32MB of system RAM in the Dreamcast.

Installation

It is necessary to replace the stock read-only boot ROM with a writeable flash ROM, as without patching the BIOS to address the modified memory arrangement, the system will not boot with RAM in a 32MB configuration.

The mod has only been tested so far using IS42S32800J-6TL replacement chips. These are readily available online, e.g. at Mouser or DigiKey.

tsowell's blog contains instructions on completing the RAM upgrade.

BIOS Flasher

A DreamShell image with 32MB-patched BIOS images is available. This image contains a variety of nearly 50 BIOS images including the stock BIOS, japanese-cake BIOS, DreamBoot BIOS, and DreamShell BIOS, in a variety of flavors for each. This image also contains an updated bflash.klf module to support flashing MX29L3211 32 megabit chips to accommodate multi-BIOS mods.

• We are not responsible for damage to Dreamcast units due to the use of this disc. Know what you are doing before you use this disc! You may render your system unbootable!
  • Download DreamShell 32MB BIOS Flasher Image

Incompatibility issues

Existing games and applications predating this RAM expansion modification will not be able to take advantage of the additional memory. Adoption of the mod is not yet widespread, so additional testing is needed. At this time, the major incompatibility issue is Sofdec video playback in commercial games. These games will fail to play FMV, often hanging or crashing as a result. More research is needed to determine if this issue can be fixed in patches. Games that don't use Sofdec video appear to work without problem, even including other types of video like the 4XM video used in Headhunter.

Applications

KallistiOS

KallistiOS currently supports 32MB expansion when using the GCC 4.7.4 (current stable) or GCC 9.3.0 (current testing) toolchains.

Applications built will function on 16MB or 32MB systems, but the programmer can support features with heavier memory use on 32MB systems. The following code block provides a primer on the use:

/* HW_MEM_16 and HW_MEM_32 macros define the memory sizes KallistiOS supports */
printf("KallistiOS supports systems with %d or %d bytes of memory installed.\n", HW_MEM_16, HW_MEM_32);

/* The HW_MEMSIZE macro can be called to retrieve the running system's size */
printf("HW_MEMSIZE reports this system has %ld bytes.\n", HW_MEMSIZE);
printf("This is a %s console!\n", (HW_MEMSIZE == HW_MEM_32 ? "32MB" : "16MB" ));

/* The DBL_MEM boolean macro is provided as a fast way to determine if the extra RAM is available */ 
printf("Does the system have double RAM? %s\n", (DBL_MEM ? "Yes!" : "No..."));

/* uint32 _arch_mem_top can be used to get the top address of memory */
printf("Top of memory is 0x%0lx!\n", _arch_mem_top);
/* 0x8e000000 if 32MB, 0x8d000000 if 16MB */

KallistiOS also includes memtest32 in its example programs. Adapted from tsowell's original utility, memtest32 supports memory testing 16MB and 32MB Dreamcasts.

DreamShell

The latest version of the DreamShell operating system, which uses KallistiOS as its kernel, now supports 32MB expansion.

NetBSD Support

NetBSD can be easily modified to support the 32MB expansion by modifying the sys/arch/dreamcast/conf/std.dreamcast file and rebuilding. Replace

options 	IOM_RAM_SIZE=0x01000000         # 16MB

with

options 	IOM_RAM_SIZE=0x02000000         # 32MB

and rebuild the kernel.

ScummVM

tsowell has written a fork of ScummVM with extra functionality which is able to play larger games on consoles with 32MB expansion. This version of ScummVM also offers an extensive array of other expansion hardware features, such as compatibility for loading/saving data with SD cards and hard drives, the ability to output MIDI over serial or the expansion slot for external synthesizers, and the ability to output various VGA modes for CRT monitors.

Game mods

A few game mods by yzb exist to increase performance:

• The King of Fighters '98
• King of Fighters XI (Atomiswave conversion)
• Knights of Valour The Seven Spirits (Atomiswave conversion)
• Super Street Fighter II X

Emulators

lxdream Dreamcast Emulator

lxdream-nitro supports 32MB expansion when run with the --ram-size=32 option.

git clone https://gitlab.com/simulant/community/lxdream-nitro.git
cd lxdream-nitro
meson setup builddir
meson compile -C builddir
./builddir/lxdream-nitro --ram-size=32