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    SubjectRe: [Linux-usb-users] [SOLVED] Serial buffer corruption [was Re: FTDI usb-serial possible bug]
    On Sun, 6 May 2007, Alan Cox wrote:

    > > However, whatever policy the buffer uses, the fundamental point it's that
    > > when I flush the input buffer I should be sure that each byte read
    > > after the flush is *new* (current) data and not old one. This because
    >
    > Define "new" and "old" in this case. I don't believe you can give a
    > precise definition or that such a thing is physically possible.

    One can come close. It would make sense to say that after a flush,
    subsequent reads should retrieve _contiguous_ bytes from the input stream.
    In other words, rule out the possibility that the read would get bytes
    1-10 (from some buffer somewhere) followed by bytes 30-60 (because bytes
    11-29 were dropped by the flush). By contrast, it would be permissible
    for the read to obtain bytes 20-60, even though 20-29 may have been
    entered the input stream before the flush occurred.

    > The hardware itself has buffers at both ends of the link, there may be
    > buffers in modems, muxes and the like as well. We can certainly flush
    > input buffers in the kernel but it isn't clear we can always do so at the
    > hardware level, let alone at the remote end or buffers on devices on the
    > link.

    This is of course the fly in the ointment.

    Alan Stern

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