Re: [Jack-Devel] JACK2 for Android newly released!

modprobe does not exist in any version of Android I have looked at. Google
is fond of monolithic kernels.

Likewise with aplay or any other ALSA utilities. However, you can mine
/proc/asound for information, at least on Nexus.

Brad Justice


On Tue, Jan 28, 2014 at 8:30 AM, Christian Schoenebeck <
[hidden]> wrote:

> On Tuesday 28 January 2014 14:23:30 김정연 wrote:
> > > support the "USB audio class" standard protocol nowadays. Support for
> > > such devices is provided by a standard Linux kernel module which is
> > > platform independent.
> >
> > Yes. android officially support USB Audio by framework level.
> > But, how to JACK access and use /dev/usb/... as audio device using jack
> > driver?
> > I have no background about that.
> > Are there any bridge between usb~alsa?
>
> Like already suggested by Patrick, you need the ALSA USB audio kernel
> module
> (modprobe snd-usb-audio), which already comes with the official Linux
> kernel.
> The driver module file should be at a location like:
>
>
> /lib/modules/KERNEL_NAME_AND_VERSION/kernel/sound/usb/snd-usb-audio.ko
>
> By the way, devices under /dev/usb are just shown if there is a compatible
> driver available & loaded on the system. Otherwise the USB device will
> never
> appear under /dev/usb at all.
>
> Once you loaded the kernel module, check whether the USB audio device is
> visible in the ALSA system, i.e with
>
>         aplay -l
>
> if yes, you can use i.e. "aplay -D DEVICENAME /foo/some.wav" to output some
> sound file to the USB audio device.
>
> If you do not have that kernel module and are not permitted to add it to
> the
> Android release, you might solve it in user space. But that would mean
> quite
> some work: Since around kernel 2.6.2x there is something called "USB file
> system" (usbfs). If that is enabled in your kernel configuration, then
> every
> USB device attached will automatically appear under /proc/bus/usb/, that
> is no
> matter whether there is a driver for it or not. usbfs allows to communicate
> with USB devices in user space, by simply conveniently opening their "USB
> endpoint" file under /proc/bus/usb/ and reading/writing to it by a normal
> application. However you might then need to write such an application on
> your
> own, by looking at what snd-usb-audio for example does or by reading the
> "USB
> audio class" protocol definition, since I am not aware of some
> daemon/application ready to be used for that purpose.
>
> If you solved that, you have the next problem: the JACK server is usually
> started with exactly one audio device. JACK2 has a slave driver concept,
> however I can't remember the details about it right now. Maybe Stéphane or
> somebody can comment it. I guess you would need to restart the JACK server
> each time a USB audio device was attached or detached, supplying the USB
> device(s) as slave device(s) at command line. Maybe you could also control
> that at runtime by dealing with JACK2's driver API.
>
> > > Are you running a hypervisor kernel like OKL4 on lowest level and
> > > Android/Linux on top of it? Or is the Android/Linux kernel running
> >
> > directly on
> >
> > > the ARM CPU?
> >
> > I have no idea about hypervisor or something.
>
> Hypervisor kernels are often used on mobile devices on lowest level. They
> are
> acting as kind of virtual machine layer for the "actual" operating systems
> running on top of the hypervisor kernel. This is usually done for two
> purposes: a) it allows multiple OSs to run at the same time, i.e. one OS
> for
> controlling embedded communication components, and in parallel the actual
> end
> user advertised OS like Android or Symbian. Further it allows b) the same
> OS
> binaries to run on a variety of hardware without modifications, saving
> development costs.
>
> So whether or not there is a hypervisor kernel running, could have a large
> impact on the question whether you are actually able to run audio apps with
> low latency at all. So you might talk to somebody responsible for kernel
> level
> issues there at Samsung to find out whether that is the case.
>
> Best regards,
> Christian Schoenebeck
> 
> Jack-Devel mailing list
> [hidden]
> http://lists.jackaudio.org/listinfo.cgi/jack-devel-jackaudio.org
>

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