Re: [PARPORT] ECP mode transfers in 2.4.x kernels

From: Dave Strauss (D.Strauss@motorola.com)
Date: Mon Sep 10 2001 - 14:06:39 EDT

  • Next message: Tim Waugh: "Re: [PARPORT] ECP mode transfers in 2.4.x kernels"

    On Fri, 07 Sep 2001 22:21:42 +0100, Philip Blundell <philb@gnu.org> wrote:
    >
    > >It's interesting that in all cases 2 or 3 bytes are added, then 32
    > >bytes later one is skipped.
    >
    > Yeah. Well, if I'm reading them right, you are always getting two bytes
    > repeated and then, 32 bytes later, two bytes dropped. So:
    >
    > ***** 4226: 0a should be 32
    > ******
    > 30,0a,31,32,33,34,35,36,37,38,39,30,0a,31,0a,
    > 0a <===
    > 31,32,33,34,35,36,37,38,39,30,0a,31,32,33,34
    > ******
    >
    > here you've got `0a, 31' repeated, and
    >
    > ***** 4259: 31 should be 30
    > ******
    > 37,38,39,30,0a,31,32,33,34,35,36,37,38,39,31
    > 31 <===
    > 32,33,34,35,36,37,38,39,30,0a,31,32,33,34,35
    > ******
    >
    > here you've lost `30, 0a'.
    >
    > Remind me whether you see the same behaviour if you disable DMA but leave
    > hardware assist enabled? (I.e. if you use parport_pc_fifo_write_block_pio.)
    >
    > p.
    >

    That's something I hadn't thought of trying. I've done so (by setting
    dma=none in /etc/modules.conf) and it works with no errors. The
    interesting thing is that it's *faster* without DMA than with DMA --
    on one printer I get 980 kBytes/sec without DMA vs 490 kBytes/sec with
    DMA (in ECP mode); on the other printer I get 540 kBytes/sec without
    DMA vs. 340 kBytes/sec with DMA. In compatibility mode it is also
    faster without DMA but not as dramatically so.

    I think at least for now I think I'm just going to turn DMA off. I'm
    still open to trying other experiments, though, if anybody wants to
    suggest something.

    -- Dave Strauss

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