TU58FS - Overview

Parent Category: Tools Category: TU58FS - file sharing with a DECtape II emulator Written by Administrator

TU58FS is "yet another" emulator for DEC's TU58 DECtape II device.

Like all TU58 emulators tu58fs runs on a Windows or Linux host and is operated by a PDP-11 or VAX over serial RS232 line.

File sharing

The big new thing with tu58fs:

    It is designed as tool to share files between any Linux host and the PDP-11.

So "tu58fs" is short for "TU58 emulator with file sharing". While normally tu58 emulators save the content of the 256KB data cartridges as one opaque binary image, tu58fs stores the data as separate files in a directory on the host.

The shared host directory and the tape content is automatically synchronized.
Since a TU58 cartridge can be changed anytime, DEC operating systems do not cache any tape content (at least not on XXDP and RT-11). The internal tape image can be changed by the synchronizer without causing inconsistencies.
Most DEC operating system access the TU58 as a "DD:" device. So if the PDP-11 writes a file onto "DD:", it appears in the shared host directory. And if the host puts a file into the shared dir, it appears magically on the DD: device. File transfer becomes very easy this way!

In fact, tu58fs combines the function of a standard TU58 emulator and a DEC filesystem manipulation tool (See DBIT's "PUTR", Don North's "xxdpdir" or Will's Work "DIAGDIR" for more). Consequently, it can also unpack a directory full of files into one image and back.

Unique features

Exchanging files between PDP's and the modern world is a permanent challenge. There are several solutions, basing on these principal approaches:

  1. transferring data on some disk or tape image file, then encoding/decoding the filesystem on the modern host.
    For transfer every medium is used which can be accessed both on the PDP and the PC side:
    image files, SDcards on drive emulators, floppies, or SCSI disks.
  2. Networked solutions: Modern host and PDP are connected over some kind of network.
    For instance DECnet is an option (http://retrocmp.com/decnet), TCP/IP goes over 2.11BSD or the Billquist port on RSX-11 (http://madame.update.uu.se/)
  3. Serial line based. There are lots of special reader/dumpers, and of course Kermit. Even PDP11GUI falls into this category.

Tu58fs understands the XXDP and the RT-11 filesystem. The RT-11 filesystem is also accessible by RSX-11, RSTS and VAX/VMs with the EXCHANGE utility.

Tu58fs is an attractive approach, as

  • it needs almost no working resources on the PDP-11 side, only a 2nd serial port additional to the console.
  • it needs no special software on the PDP-side, only the DD driver. This means small memory footprint.
  • it is very easy to operate: file share just with the "COPY/DIR/DELETE" commands of the used operating systems.
  • the PDP-11 can directly boot from a set of host files.
  • under XXDP and RT-11, a virtual tape image can be "oversized" and contain up to 32MB of data. Physical TU58s and many emulators allow only for a media size of 256KB per cartridge.

Code download

tu85fs is written in C for Linuxes, and hosted on GitHub at https://github.com/j-hoppe/tu58fs.
Also for download are ready-to-use setups to run full XXDP diagnostics and full RT-11 from oversized tape.

Some guys build physical TU58 emulators, with SDcards or TCP/IP to move the tape images out.
tu58fs can be used for these applications too: it compiles on all the embedded Linuxes, and direct ssh/ftp access to the "files on the tape" is
more comfortable than dealing with the downloaded images.

And last but not least: I used Don North's latest TU58 protocol engine, as published at https://github.com/AK6DN/tu58em.
Thanks, Don!