On Sun 6 May 2007 12:01, Robert Schwebel pondered: > 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.
Yes - there are too many applications which require tight/sync connection with the data - control loops, software radios, machine control, etc - all have much different needs than audio, hwmon, or touchscreen. > 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 I am assuming that the driver takes care of all DMA/coherency issues that might pop up? (and handles all interrupts)? > - 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. I would guess that something like v4l might be the best bet - the driver provides a few mmapped buffers that you can read/write into, and some mechanism to sync in/out of the buffers. I was actually looking at UIO, but thought that since we really desire the kernel ring buffers, that a think model might be better.? http://www.kernel.org/pub/linux/kernel/people/gregkh/gregkh-2.6/gregkh-01-driver/uio-documentation.patch -Robin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/