P1394 Mail Archive: Re: P1394> Generic PPDT Device

P1394 Mail Archive: Re: P1394> Generic PPDT Device

Re: P1394> Generic PPDT Device

From: Peter Johansson (PJohansson@ACM.org)
Date: Thu Aug 03 2000 - 15:05:40 EDT

  • Next message: Peter Johansson: "P1394> Isochronous SBP-2"

    At 11:36 AM 8/3/00, RICE,CHUCK (HP-Vancouver,ex1) wrote:

    >At the July meeting in San Francisco we had talked about going to Fry's,
    >purchasing two PPDT devices and being able to hook them together and
    >print. Because of the nature of SBP-2, one of the devices needs to have
    >initiator capabilities. Does this require that we mandate in the printer
    >profile that the printer be both initiator and target? Or do we mandate
    >that non-printer devices be initiators? Will there be PPDT scanners and
    >still cameras that will implement initiator functionality? Or will there
    >be different levels of compliance?

    The ironic twist to this discussion is that it is likely easier to be an
    initiator than a target!

    Clearly, the only safe thing to do is to build a PPDT device to be both
    initiator and target. Given the belief stated above, this may be the
    simplest thing to do.

    But let's suppose it isn't. How do you reach consensus as to which devices
    SHOULD or SHALL (the distinction is a separate discussion I want to avoid
    for the moment) support which capabilities?

    I suggest that we do NOT base the discussion on conventional wisdom as to
    which device is the controller (initiator) and which is the controlled
    device (target). I think a better analysis could come from the questions:

    1) Which device is more "naturally" suited to have the buffer memory for
    the whole task?

    2) Which device is more concerned with the pacing of data transfer during
    the task?

    Initiators tend to have the memory for the task, targets tend to be
    concerned with the pace of data transfer. Even this is not a hard and fast
    rule, as the data buffers may be located in a third party.


    Peter Johansson

    Congruent Software, Inc.
    98 Colorado Avenue
    Berkeley, CA 94707

    (510) 527-3926
    (510) 527-3856 FAX


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