[Jack-Devel] Implement a driver as a writable client?

[Paul Davis]

You can't do duplex properly as a client. The main difference between a
JACK "driver" (aka "backend") and a client is that a driver consists of two
halves. One is executed at the start of a process cycle, to collect data
from the hardware; the other is executed at the end of a process cycle, to
deliver data to the hardware.

If you're not doing duplex, you can do whatever you want in a client, but
keep in mind that it cannot block, meaning that you basically have to
shuffle the data to/from another thread that actually interacts with the
hardware.


On Fri, May 13, 2016 at 7:12 PM, Chuckk Hubbard <badmuthahubbard at gmail.com>
wrote:

> Hi.
> I've been sinking lots of time in trying to get ALSA to work with a
> SGTL5000 (Teensy Audio Adapter) in Raspbian on a Raspberry Pi 3. I have the
> complete documentation for how to manually set up the audio chip, and
> sufficient documentation on how to manually set up the Pi's ARM I2S
> peripheral. The ALSA solution is generalized for any kind of hardware you
> could want, is something I don't really want to know, at all, in my life,
> and seems just far too complex when I have detailed guides for both the
> audio chip and the CPU. The one combination of ALSA platform, machine and
> codec drivers that I've managed to get sound from plays more than 2x too
> fast and will not open with JACK.
>
> So, I'm reading about the JACK API, wondering about simply writing a C
> program to configure and write to the Pi's built-in I2S FIFOs, without even
> telling ALSA that I'm doing it; but I see that all JACK clients should use
> callback functions. Still, audio input from JACK into a program using the
> API is a regular thing, right? So how complicated might it be to set up
> such a client that gets audio input from JACK and writes that to the chip's
> I2S FIFO? My timing will be controlled by the audio chip, the Pi chip will
> be a slave to it. So as long as my program writes to the transmit FIFO fast
> enough, and waits if the FIFO is full, I think I don't need to worry about
> synchronizing JACK exactly to the audio chip's clock... right?
>
> I'm just a little fuzzy on this timing part.
> Thanks for any clarification.
>
> -Chuckk
>
>
> --
> http://www.badmuthahubbard.com
>
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>
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