rdist

September 21, 2010

Building the ZoomFloppy slides

Filed under: C64,Embedded,Hacking,Hardware,Retrocomputing — Nate Lawson @ 2:50 pm

At ECCC 2010, I presented these slides on the ZoomFloppy, a new device for accessing Commodore floppy drives from a PC via USB. The firmware, known as xum1541, has been available since fall 2009 for those who want to build their own board, but the ZoomFloppy is the first device that will be a complete product offered for sale. Jim Brain will be manufacturing and selling it by the end of the year.

The ZoomFloppy has a number of features beyond simple disk access, which is implemented in OpenCBM. It can also nibble protected disks using a parallel cable and nibtools. It is software-upgradeable and this presentation discusses some features that are planned for the future.

One surprising finding I made was that by running the 1571 drive in double-clocked (2 MHz mode), the hardware UART is just fast enough to enable transfer of raw bits, directly off the media. No one has every created a copier that took advantage of this “hidden” mode in the 25 years since the 1571 was introduced. Normally, this kind of transfer requires soldering a parallel cable into your drive. This mode works via the normal serial cable, but requires low-latency control of the bus that is only possible with a microcontroller (not DB25 printer port).

I also discuss how modern day piracy on the PS3 affected our chip supply and digress a bit to discuss old copy protection schemes. I hope you enjoy the presentation.

(Direct pdf download)

6 Comments

  1. Hello Nate,

    one clarification/addition:

    On Slide 13, you write:
    “Infinite listener hold-off
    – To support printers …”

    This not only affects printers or other “slow devices”: Even the 1541 will take approx. 90 seconds in one case. It is a crucial part of the protocol to give the device time to finish what it is currently doing.

    – Spiro

    Comment by strik — September 21, 2010 @ 10:32 pm

    • That is true. Anyway, the xu1541 can never support this due to its USB protocol. It would have to be rewritten to start a command in one control msg and then poll for completion with another.

      Comment by Nate Lawson — September 27, 2010 @ 12:36 pm

  2. Could you also put up a non-flash version? I spent half a minute looking for the download link before I decided to check the page source.

    Comment by igorsk — September 22, 2010 @ 2:04 am

    • A link to this has been added at the bottom of the post.

      Comment by Nate Lawson — September 28, 2010 @ 2:32 pm

  3. I just found out that I have an old 1571 drive (original, unmodded) and I would LOVE to use the “ZoomFloppy” to transfer and preserve my old disks.
    Whom can I ask for the complete product – and when will it be released and for sale, anyway?

    Comment by Antitrack — October 24, 2010 @ 8:55 am

    • Jim Brain will be producing it. However, it won’t be available for sale (or otherwise) for a few months.

      Comment by Nate Lawson — October 24, 2010 @ 9:58 pm


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