ZPLinux

A tailored Linux release for my 486 FreeDOS machine.

(Toolchain and distro built with Docker)

(Yeah, that's cmatrix burning the 66Mhz CPU)

Comes in two lovely floppy diskettes.

Changelog

v0.1

Initial Release

v0.2

Added Real Time Clock support in the kernel.
Safer toolchain (without LDFLAGS="-s") / binaries and .so are now stripped via *strip --strip-unneeded at the end of toolchain build process.
Removed most of built static libraries - going fully dynamic whenever applicable.
Copied libc.so to the modules floppy - the script now creates the symlinks for the interpreter /lib/ld-musl-i386.so.1 and /bin/ldd.
Non-boot diskettes are now ext2 formatted.

Target Machine

Motherboard: Jetway-437 (VESA, PCI)
CPU: Intel 486 DX2 - 66Mhz
RAM: 4x4MB EDO RAM (16MB)
VGA: S3 Virge/DX 4MB
Sound: Creative SB16 Vibra PnP (ISA)
Network: RTL8029AS
HDD: Samsung WN312021A (1,2GB)
CD-ROM: LG GCR-8520b
Floppy: 3.5” 1.44MB
Keyboard: DYN5 UK Keyboard
Mouse: Microsoft Serial Mouse (2 buttons)

Screenshots & Videos

Boot time from when the floppy is triggered to usable shell (around 1m27s).

Full cold-boot video

IMG_1614.mov

More Screenshots (QEMU)

Kernel Configuration

Modules are a must - it's impossibile to fit everything into a floppy. The non-essential modules will be offloaded to the second floppy.

- Enable loadable module support
- Enable block layer
- General setup -> swap 
- General setup -> initramfs/initrd support (gzip only)

Some generic must-have features

- General setup -> Kernel Features (expert) -> printk
- General setup -> Kernel Features (expert) -> PC-Speaker
- Executable file formats -> ELF binaries
- Executable file formats -> Scripts starting with #!
- Device drivers -> Generic driver options -> devtmpfs

Processor configuration

- Processor -> Family -> 486DX
- Processor -> Load address -> 0x400000

The motherboard supports both ISA and PCI, so...

- Bus -> ISA support
- Device drivers -> PCI support

For the block devices, the machine uses SCSI/PATA.

- Device drivers -> Block devices -> Normal floppy support
- Device drivers -> SCSI -> SCSI device support
- Device drivers -> SCSI -> SCSI disk support
- Device drivers -> SCSI -> SCSI CDROM
- Device drivers -> SATA/PATA -> ATA SFF support
- Device drivers -> SATA/PATA -> Generic platform device PATA support
- Device drivers -> SATA/PATA -> Legacy ISA PATA support

For the VGA (module)

- Device drivers -> Graphics -> Framebuffer support -> S3 Trio/Virge

Filesystems (ext2, fat, vfat and ISO9660)

- File systems -> EXT2                  
- File systems -> CDROM -> ISO9660                  
- File systems -> DOS/VFAT/etc -> MSDOS                  
- File systems -> DOS/VFAT/etc -> VFAT                  
- File systems -> Pseudo -> /proc                  
- File systems -> Pseudo -> sysfs                  
- File systems -> NLS -> Codepage 437                  
- File systems -> NLS -> ISO 8859-1

Mouse (module) and keyboard

- Device drivers -> Input device support -> Keyboards -> AT
- Device drivers -> Input device support -> Mice -> Serial

Sound card (Vibra16 - ISA PnP)

- Device drivers -> PNP support -> ISA PNP   
- Device drivers -> Sound card support -> ISA devices -> SB16 PnP

Parallel port (module)

- Device drivers -> Parallel port support -> PC-Style hardware

PC speaker (module)

- Device drivers -> Input device support -> Miscellaneous -> PC Speaker

TTY

- Device drivers -> Character devices -> TTY
- Device drivers -> Character devices -> TTY / Output messages to printk

Busybox settings

TBW

Docker images

Provided files

busybox-config and kernel-config are self-explanatory.
busybox-init is the main initramfs script.
entrypoint.sh is the entrypoint script for the zplinux image that builds kernel and busybox, and also creates the floppies.
floppy.img is a dump of a physical floppy diskette, formatted under FreeDOS 1.3RC5 and with Syslinux 4.x installed on it

486toolchain

This image builds a i486-linux-musl-* prefixed cross-compiler toolchain in /toolchain.

It is the base image for the zplinux one.

Cross-compiled libraries:

ncurses
zlib
lixml2
gettext
gzip
bzip2
readline
PCRE
libffi
GLib2

zplinux

This image compiles and packages the kernel and busybox at build time.

The floppy disk(s) are created at runtime by the entrypoint script.

Running

# Build toolchain image (grab a coffee)
docker build -t 486toolchain ./486toolchain 
# Build zplinux image
 docker build -t zplinux ./zplinux
# Finalise zplinux build (privileged is required to mount the floppies)
docker run --rm -ti -v /some/output/folder:/data --privileged zplinux

# Once the floppy is built, copy it to /data
docker-machine> cp /floppies/*.img /data
docker-machine> exit

# Flash it (or test it in QEMU - see below)
sudo dd if=/path/to/zplinux.img of=DEVICE bs=512 count=2880 conv=noerror,sync

QEMU

qemu-system-i386 -cpu 486 -m 16 -fda zplinux.img

Must Read

Articles that inspired my Linux quest:

Floppinux - An Embedded 🐧Linux on a Single 💾Floppy by Krzysztof Krystian Jankowski
Linux on a 486SX by Ocawesome101

matteo-pacini / ZPLinux