Boot Dreamcast Linux with QEMU

Boots the images of Modern Linux on the Dreamcast with qemu. And does nightly integration against mainline linux-next, with 2 known or soon to be upstreamed patches.

Build

Only the sh4-softmmu target is needed. From the source root:

./configure --target-list=sh4-softmmu --enable-slirp --disable-docs
ninja -C build qemu-system-sh4

--enable-slirp provides the user-mode network backend for the Broadband Adapter / LAN Adapter. The binary lands at ./build/qemu-system-sh4. After editing sources, rebuild incrementally with ninja -C build qemu-system-sh4.

Build dependencies are the usual QEMU ones (a C toolchain, ninja, python3, glib + pixman dev packages); on Debian/Ubuntu:

sudo apt install ninja-build python3 pkg-config libglib2.0-dev libpixman-1-dev

Run

./build/qemu-system-sh4 \
  -M dreamcast -m 16 \
  -serial null -serial stdio \
  -kernel /home/flo/devel/t2-hacking/dreamcast/dreamcast-linux/.dreamcast/src/linux-7.1.3/vmlinux \
  -drive if=none,file=/home/flo/devel/t2-hacking/dreamcast/dreamcast-linux/build/linux-7.1.3-with-userland-musl.iso,format=raw,readonly=on

Disc image formats & booting from disc

The -drive disc image may be either a raw ISO9660 (.iso) or a DiscJuggler .cdi (audio session + scrambled data track, as produced by cdi4dc). The type is auto-detected.

Passing -kernel boots that kernel and uses the disc only as the root filesystem. Omit -kernel to boot the disc itself the way a real Dreamcast does - the emulator finds 1ST_READ.BIN in the ISO9660 root, descrambles it, and runs it from 0x8c010000:

./build/qemu-system-sh4 -M dreamcast -m 16 -serial null -serial stdio \
  -drive if=none,file=linux-7.1.3-with-userland-musl.cdi,format=raw,readonly=on

NIC Support

LAN Adapter

-nic model=dc-lanadapter

BBA rtl8139too

is the default selection.

VMU (Visual Memory)

A VMU is attached as a second -drive if=none (the first is the GD-ROM). It appears as a memory card in a controller's slot on Maple port 2 and shows up in Linux as a 128 KB MTD device (/dev/mtd0, vmu-flash + vmufat).

The image must be exactly 128 KB and writable (raw, not readonly):

dd if=/dev/zero of=vmu.bin bs=1024 count=128

-drive if=none,file=/path/to/game.iso,format=raw,readonly=on   # GD-ROM (first)
-drive if=none,file=vmu.bin,format=raw                          # VMU (second)

Inside Linux the flash is at /dev/mtd0 and can be formatted/mounted with vmufat. Writes persist back to vmu.bin on the host.

VMU LCD

The VMU's 48x32 monochrome LCD can be shown as a second display (a separate GTK tab / SDL window). It is opt-in via the vmu-lcd=on machine option and needs a VMU -drive:

-M dreamcast,vmu-lcd=on

The kernel registers it as /dev/vmu_lcd0; write exactly 192 bytes (48x32, 1bpp, MSB first) to update it, e.g. the driver draws a Tux splash on attach. With -display none the LCD console can be captured over QMP/monitor with screendump file.ppm -d vmu (the VMU device id is vmu).

Supports

• Booting Linux with serial console
• GDROM (raw .iso and DiscJuggler .cdi; boot from disc via 1ST_READ.BIN)
• LAN Adapter Networking
• BBA (RTL8139) Networking
• X Framebuffer
• Maple Keyboard, Mouse
• VMU (Visual Memory) as an MTD / block device
• VMU LCD as a second display (vmu-lcd=on)