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    SubjectRe: TTY_FLIPBUF_SIZE too low causing dataloss on too fast serial lines?
    On Wed, 26 May 1999, Theodore Y. Ts'o wrote:
    > I simply haven't see much demand or practical application for high-speed
    > serial transfers. It's restricted to short distance unless you use
    > *very* expensive cables, and you can get better performance more cheaply
    > simply by using Ethernet instead. 10 Megabit ethernet cards are dirt
    > cheap, and Cat 5 UTP cables are much, much cheaper than high-quality
    > serial cables, and you can run them for a much greater distance without
    > worrying about noise or signal degredation problems.

    The one exception is embedded systems (to which Linux is beginning to
    catch on).

    In our HW, we have 6.25 Mbaud serial ports. They can be used to talk to
    other stuff on the board, or with other similar CPU's. They can also talk
    with the lower standard speeds, like 1.8 Mbaud and below.

    So in our Linux driver, I'm using the serial port DMA to send incoming
    data into a static buffer which is, when the DMA is finished, copied into
    the flip buffer and the flip call is made. On the sending side, DMA is
    started directly from the xbuf.

    Now, I know this is a waste of buffers and copyings and power, but it
    works for now. However maybe I can optimize it by starting DMA directly
    into the flipbuf or bypass the flipbuf - mayby you have a hint (I'll check
    that Rocketport driver btw).


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