Raspberry Pi Floppy Driver Uncovers Fishy Secrets

A forum post by New Zealand electronics enthusiast [zl2wrw] about retreiving waypoints from a mysterious floppy disk caught our eye. The navigation system on his friend’s fishing boat had died and was replaced. But the old waypoints were stored on a 3-1/2 inch floppy disk that was unreadable on a normal PC. Not to be deterred, [zl2wrw] then looked for another solution — apparently a list of hot NZ fishing spots is worth quite the effort.

The tool he discovered, and the main point of this story, is the bbc-fdc by [Jasper Renow-Clarke] aka [picosonic]. [Jasper] made this project to read 5-1/4 inch Acorn DFS floppies from his BBC Micro. But bbc-fdc can be used to read a variety of floppy disk formats, such as DOS, C64, Apple II, and others It can also just capture raw magnetic flux transitions on the disk, blissfully unaware of any logical structure to the data. We recently wrote about another Raspberry Pi Floppy Drive Controller project by [Scott Baker]. What sets [picosonic]’s project apart is that he’s not using an FDC controller chip here. The only interface electronics is a couple of open-collector 7406 ICs. Data is read using the SPI peripheral. If you need to archive old floppy disks or do a forensic analysis of unknown disks like [zl2wrw], then one of these two projects will almost certainly do the trick.

Meanwhile back in New Zealand, [zl2wrw] discovered that the floppy format was standard (Modified Frequency Modulation, MFM) by examining the raw flux dump. However, the filesystem was a mystery — it didn’t quite match any of the usual suspects. So [zl2wrw] dug into the hex dump of the data and figured out enough of the structure to manually recover the waypoints. Subsequently, a user on the forum found a document describing the file system used by Furuno GPS units, which proved to be a close match albeit after the fact. Alas, [zl2wrw] hasn’t publish the coordinates of those good fishing spots.

Have you had any successes (or failures) when it comes to reading data from old disks? Or have you encountered peculiar disk formats and/or file systems, where having a tool like this could have been helpful? Let us know in the comments below.

13 thoughts on “Raspberry Pi Floppy Driver Uncovers Fishy Secrets

  1. I worked about 20 years ago on computerized knitting machines and was asked to do a similar forensic analysis on the floppy disks used by another firm. To make a long story short, they had modified their PC floppy controller to use a 14.xx MHz crystal instead of a 16 MHz one – I discovered this by just looking at the raw data via a scope. Modified a PC’s floppy controller to use a similar crystal & the data was read/writable.

        1. I can’t believe there was a software manual for the Tandy drive. It would have been so much easier connecting it to a good computer rather than to the Model 100 and doing transfers.

          I did disassembled the program that loaded into the Model 100, but I didn’t make much progress. As I recall, it seemed to use packets along the serial interface. Then I read that one of the magazines had run a two part article about it, so I ordered copies. But I scrapped the project eventually. This was all in the eighties.

          I still have the drive somewhere.

    1. Back in the 1990s, I was roped into being the unofficial tech support guy for a small office. The office manager was a very sharp lady, but not a tech geek. One day, out of the blue, she asked me for help with RS-232 communications. As I started answering, I suddenly realized there was nothing in the office that used serial ports. I asked, “Diane, why do you need to learn about RS-232?” Turns out she had recently bought a new specialized sewing machine, and it had an option to use RS-232 commands to control stitch patterns instead of those old mechanical cams. I wonder if those ever came with a floppy disk option?

      1. I tried for a long time to get my mother to give me her cam driven machine. I had the idea early to put a solenoid and a position sensor in place of the cam and hook it to my 1802 based computer. It was so obvious an idea I knew someone would do it.

        Glad to hear someone did.

  2. I have a similar project which has shown up here before, the FluxEngine; the client for this supports my own hardware and also the GreaseWeazle, and I’d love to support more. Provided the hardware’s native protocol can be translated to what the FluxEngine client expects that’ll give you a all-in-one solution which will encode and decode a variety of formats, including wacky GCR stuff like 800kB Mac disks.

    1. I’ve still got a stack of fresh 5″25 floppies sealed in their boxes. There is no sound in this world more pleasing then the sound for the 1541 reading a disk.

  3. as someone who lives in a fishing town, i know how some fishermen are about their fishing spots. they wont tell anyone, they wont make backups for fear that they will get stolen and keep the original on their fishing boat. i have a couple spots of my own that i wont tell anyone about and im just a guy with a rod. for commercial fishermen its their bread and butter to know when and where the fish are and if they have some scrap of knowledge about some subsurface terrain feature that is a halibut hangout, they are going to keep it to themselves.

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