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    SubjectRe: audio/PCI/mmap oddity (again)
    Paul Barton-Davis wrote:
    >
    > one other interesting note about this problem. it only occurs when the
    > PCI soundcard is writing 16-bit samples to the ADC buffer, never when
    > its writing 8-bit samples.
    >
    > i have no idea what this could mean. oh, and the frequency is much
    > larger than i said last time - more like 10-20 times in 512 patterns.
    >
    > --p

    PCI cards usually use busmaster DMA, and do transfers in bursts. (es1370
    for example: always 32 bytes/burst. Cards with real DSPs like the TB
    MultiSound "Hurricane architecture" series, are usually fully
    programmable from the driver.)

    If the distance between the patterns is less than the buffer size; this
    will happen every now and then:

    1. You read pattern n. Not overwritten.
    2. DMA burst overwrites pattern n AND pattern (n + 1).
    3. You read pattern (n + 1), which has now been overwritten...

    Pretty much the same kind of phenomena as video tearing, or interprocess
    communication sync problems.


    //David

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