Re: documentation

[Guilhem Tardy <guilhem_tardy@yahoo.com>]

Hi,

Now, I have this new driver which manages to open/close a pcm channel whenever
one attempts to play a file with "play test.au", but complains (Sound protocol
it not compatible) with "aplay test.au". Any idea what's wrong?
Besides, I have no mixer defined (I would just to allow open/close a playback
or capture channel, no more) and wonder if it is a problem?
I am just loading the driver manually for now (insmod snd, snd-timer, snd-pcm,
...), is there any special configuration I need? How to tell the driver to
unmute?

Thanks,
Guilhem.

> > > the copy and silence ops are called when write() is called (more
> > > exactly on alsa it's ioctl) - the thread writing to the device does
> > > actually work like DMA.  on mmap mode, there is no such one.  so you
> > > need an extra thread (or if it's not too heavy then tasklet might be
> > > available) anyway.

> no, i posted to alsa-devel ML, a month ago or so.
> the document you read is for the user library, not for the driver.

> in your case, you need to copy the data on the buffer to the hw by
> yourself.  then what is the merit of mmap? 
> (well, it would be a bit more efficient than copy_from_user(), but
>  the advantage of copy_from_user() is that you can use non-contiguous
>  buffer while alsa's mmap supports, so far, only contiguous region.)

> on alsa, when the program runs in the mmap mode, no read/write is
> called but the data is read/written on the mmapped buffer, and the
> also mmaped status is updated.  during the app writes data, DMA
> transfers the data from the mmaped buffer.
> that is, the thread is free from the kernel mode.


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