ppcopy

Copy files over the parallel port using Linux and DOS and a LapLink cable.

The typical use is getting files onto an old DOS machine that has no other way in: no network, no working floppy drive, no USB. The DOS programs are a few hundred bytes, small enough to type in by hand with the DOS DEBUG utility, and after that the cable does the rest.

Getting the programs

Download

Prebuilt binaries are on the releases page. Each release contains:

• ppread.com and ppwrite.com for DOS
• ppread-i386, ppwrite-i386, ppread-x64, and ppwrite-x64 for Linux. These are statically linked and run on any distribution.

Build from source

You need GCC and NASM. Then:

make

This builds ppread and ppwrite for Linux and ppread.com and ppwrite.com for DOS. Use make linux or make dos to build only one side. See HACKING.md for other build variants.

Copying a file

The commands are the same on Linux and DOS. Connect the LapLink cable between the two machines, then start the receiver first:

ppread > output

Now, on the other machine, send the file:

ppwrite file

Any combination works: Linux to DOS, DOS to Linux, DOS to DOS, or Linux to Linux.

On Linux the programs talk to the port directly, so they must run as root:

sudo ppread > output
sudo ppwrite file

ppread always writes the received data to standard output, so it must be redirected to a file. Error messages go to the screen and never end up in the output file. On DOS the errorlevel is 1 if anything went wrong, including running out of disk space.

Bootstrapping a DOS machine with no media

If there is no way to copy ppread.com onto the DOS machine, you can type it in with the DOS DEBUG utility. The default build is 237 bytes. A build with PORT_ARG=0 drops the port argument and gets it down to 190 bytes; see HACKING.md for the build flags. Once ppread.com is on the machine, use it to receive everything else, including ppwrite.com.

Using a different parallel port

All programs use the parallel port at I/O address 378 (LPT1 on most machines) unless told otherwise. To use a different port, give its base address in hex as the last argument. It is the only argument to ppread and follows the file name for ppwrite, on both Linux and DOS:

ppwrite file 278
ppread 278 > output

The usual addresses are 378 for LPT1, 278 for LPT2, and 3bc for the port on an old monochrome display adapter. The Linux programs also accept a 0x prefix.

The DOS programs do not check the address for typos: anything that is not a hex digit is silently taken as one. Builds made with PORT_ARG=0 ignore the argument entirely and always use 378.

More

• HACKING.md: build variants, DOS debug builds, making a release, running the tests.
• PROTOCOL.md: the wire protocol.
• qemu-device/README.md: a QEMU device that emulates a LapLink cable between two virtual machines.