Utility to read RX50 Teledisk images on RSX systems

The DEC RX50. Has there ever been a more disliked peripheral in the DEC world? Well, of course there has - the TK50. But we're talking about the RX50 today.

  The RX50 is a dual 5-1/4 inch floppy drive that found its way on to a lot of DEC gear in the 80s. RX50s were used on the DEC Professional computers (325s, 350s and 380s), on DECMates and on lots of smaller PDP11 and VAX systems.

  A lot of software from that era (including a lot of software for DEC machines on RX50s) wound up being archived by a program called "Teledisk". Teledisk was a pretty capable utility for saving floppies to files. It had a lot of bells and whistles for preserving all sorts of arcane floppy formats and hardware quirks. Teledisk is no longer sold or maintained, and the old versions you can find on the web run only under DOS on slow PCs (and, I hear, assorted emulators).

  I occasionally run across RX50 images that have been preserved via Teledisk (usually, files with extension .td0 are Teledisk images).  Not all of these are available elsewhere as simpler images. I could have gotten an old version of Teledisk and an old PC or emulator - but, I'm DEC blue through and through - I'd rather eat a spoonful of dirt than use a solution like that.

  Instead, I wrote an RSX utility that can read Teledisk images of RX50s and write them out as a disk image in LBN format - the format used by VCP (the RSX virtual disk program), LD disks on VMS,  and simh virtual disks. It can also write the image in track and sector order, if you have need of that.

  RTD (for ReadTeleDisk) is written to work only with RX50 images, and has only been tested with RX50s that had a Files-11 (that is, RSX or VMS) file structure. If anyone needs support for something else let me know and I'll add it in the next version.

  Note - I just found out that there is an "advanced" version of teledisk, that produced file images of RX50s that RTD can't read. I'm working on a new version than can read these advanced images.

RTD.MAC

To make...
mac rtd=rtd
tkb
TKB>rtd=rtd
TKB>/
Enter Options:
TASK=...RTD
//

To use...
>run rtd
RTD>outfile=infile
or install it
>ins rtd
>RTD outfile=infile
outfile extension defaults to .dsk, infile extension to .td0

Switches are /LBN and /TS. /LBN is the default and outputs the dsk file in logical block order. /TS outputs in ascending track, sector order. /LBN is the default because that's what you'll want to use the dsk file as a simh virtual disk or a VCP virtual disk. /TS order is for...I don't know what it's for. Can't think of any use for it, but, I included in case it's ever needed.

  So, you copy your .td0 image file to your RSX system (via DECnet, FTP binary, or whatever). You use RTD to create the DSK file, and then mount and read it using VCP or simh. What could be simpler?

 The info about the format of the teledisk file I needed to write this utility was found in an article by Dave Dunfield, at http://www.classiccmp.org/dunfield/img54306/teledisk.htm.