Re: [PARPORT] Reverse engineering a parallel device protocol

From: Matt Roberds (
Date: Sun Oct 28 2001 - 13:32:59 EST

  • Next message: Joost Kooij: "Re: [PARPORT] Reverse engineering a parallel device protocol"

    >I own a Rome mp3 player ( that connects to the PC
    >via a parallel port. Unfortunately the software is only available for
    >MS-Windows. [...] I guess the first step is to find a way to 'sniff' the
    >parallel port while using the Windows 98 software in order to find out
    >how it works.

    IF you can get a DOS driver for it, dosemu has this capability built
    in. In the dosemu config file, you can turn on access to certain I/O
    ports and also specify that all reads and writes to a particular port
    get logged to a file. The problem is usually getting the DOS driver.
    I did this with a CompactFlash card reader that was old enough that
    there was a DOS driver for it, but your MP3 player may not have a DOS
    driver available.

    >Another solution would be to twiddle a bit with some hardware to read
    >the port results, but yet I don't know much about this matter.

    If you're rolling in money just go buy or rent a logic analyzer. This
    is basically a device with several input wires that records the state
    of each wire at a defined interval. You'd connect its input wires to
    the input and output pins of your parallel port, plug in your MP3
    player, and do transfers. The analyzer would log the session and you
    could examine it later.

    Theoretically, you should be able to do the same thing with another
    PC, using the parallel port on the second PC to monitor the
    communications between the first PC and the MP3 player. I don't know
    if detailed directions exist anywhere for doing this; I haven't tried
    it myself. The second PC's parallel port has to be capable of 8-bit
    input (most recent PCs do) and has to be at least as fast as the one
    on the first PC.
    >Also, I was wondering what you guys are thinking about the legal
    >issues involved with such a hack (that's nothing else than reverse
    >engineering), and whether it is safe to do this outside the US.

    I am not a lawyer and this is not legal advice. It depends on where
    you are but it's probably OK to do it outside the US. Also, if you
    do get something working, make sure that both linux-parport and the
    popular MP3 sites know about it, and have it for download if possible.
    Once you've let it out of the bag, and at least one other person has
    downloaded it off the Net, no lawyer can stop it -- see DeCSS. All
    of this is my own personal opinion only. I am not a laywer and this
    is not legal advice.

    Good luck!

    Matt Roberds

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