Re: [PARPORT] DMA and the parallel port

From: Gora Mohanty (
Date: Sat May 03 2003 - 22:18:56 EDT

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    Tim Waugh writes:
    >On Fri, May 02, 2003 at 11:34:23PM -0700, Gora Mohanty wrote:
    >> Is it really true that the speed difference is negligible?
    >Well, it's only really true for bulk transfers in a defined IEEE 1284
    >transfer mode like ECP, to be fair. For custom protocols it will be
    >much slower in user-space, but for IEEE 1284 modes: it depends. When
    >user-space write()s a large amount, the kernel is doing the transfer
    >protocol stuff anyway, so in that sense the difference should be
    >negligible for that situation.
    >Basically I imagine it depends how much of the logic is in user-space.

    OK, that makes perfect sense. As we are using a custom protocol, at some
    point I will try and move to kernel space. I will report back on how much
    that improved things, but it might take me a little while. Thanks also
    for the information on the max. no of parallel ports supported.


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