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    SubjectRe: Correct location for ADC/DAC drivers
    On Sun, May 06, 2007 at 02:19:59PM +0200, Bodo Eggert wrote:
    > Since you ask for random thoughts:
    > IO of data streams from or to a DAC/ADC is essentially what soundcards do.
    > I'm wondering if these cards are similar enough to use alsa, and if using
    > that interface would ease or hinder programming the driver.

    I had a short look at ALSA and it looks like it is a little bit too
    focussed towards "normal" audio. For example, if follows an asynchronous
    model in the sense that an application can read/write to a buffer at any
    time, taken that the ringbuffer doesn't overflow. That's not enough for
    example for control applications; you need the option for real
    synchronous operation there.

    IMHO we need an API which offers

    - kernel ring buffers (to make it sure no data gets lost)
    - generic data types (streaming plain ADC values is just the simplest
    case; we also have for example streaming FPGA data containing
    preprocessed data sets)
    - optional timestamping for each sample
    - zero-copy from hardware into userspace memory, with DMA support
    - application notification every N samples (N >= 1)

    v4l2 may also be worth a look; but in the end I suppose they are all
    specialized sub-cases of what we'd need for fast DAQ.

    Dipl.-Ing. Robert Schwebel |
    Pengutronix - Linux Solutions for Science and Industry
    Handelsregister: Amtsgericht Hildesheim, HRA 2686
    Hannoversche Str. 2, 31134 Hildesheim, Germany
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