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.

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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.

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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)

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Screenshots & Videos

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

Full cold-boot video

IMG_1614.mov

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More Screenshots (QEMU)

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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

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Busybox settings

TBW

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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.

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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