Introduce AVTP Audio Format (AAF) plugin

Hi all,

The AAF plugin RFC series v2 has been around on alsa-devel ML for more than two weeks so I'm moving forward and sending it as PATCH series now.

The first 5 patches from this series are pretty much the same from the previous version. The news are the top 2 patches which add more functionality to the plugin. Patch 6/7 implements the dump() callback which has been useful for debugging purposes and Patch 7/7 adds support for direct read/write transfers.

For general context information about the AAF plugin, I'm quoting below the cover letter from the RFC series v1:

"This patchset introduces the AAF plugin to the alsa-plugins project which enables TSN audio applications on Linux.

For those not familiarized with TSN, it stands for Time-Sensitive Networking, and it's a set of IEEE technologies (enhancements to IEEE 802.1Q and Ethernet protocols) that provide precise time synchronization, bounded latency and application interoperability to bridged networks. Those technologies enable time-sensitive applications such as audio, video and control loops to run on top of bridged networks, co-existing with regular applications. TSN technologies are a super set of Audio Video Bridging (AVB) technologies also developed by IEEE. AVTP is the protocol defined to transport data in a TSN system, and AAF is one of the formats defined by AVTP to encapsulate audio data. AAF is specified in Chapter 7 from the AVTP spec [1].

This work is part of the effort to enable TSN technologies on upstream Linux ecosystem. All building-blocks required to enable TSN audio applications have been already developed and pushed to upstream projects. Time synchronization features are provided by linuxptp project [2], bounded latency features are provided by Linux Traffic Control subsystem since kernel version 4.15 [3], and AVTP packetization is provided by libavtp [4]. What is currently missing in the ecosystem to enable TSN audio applications is a piece of software that plumbs it all together and interfaces with Linux Audio system properly. That's the point of the AAF plugin introduced here.

The AAF plugin is a PCM plugin that uses AVTP protocol to transmit / receive audio data through a TSN capable network. When operating in playback mode, the plugin reads PCM samples from the audio buffer, encapsulates into AVTP packets and transmits to the network, mimicking a typical AVTP Talker. When operating in capture mode, the plugin receives AVTP packets from the network, retrieves the PCM samples, and present them to alsa-lib layer at the presentation time, mimicking a typical AVTP Listener."

For further information about what has been previously discussed, please refer to RFC series v1 and v2 archives in [5] and [6]. Finally, all versions of this series can be also found in my alsa-plugins tree in github [7].

Best regards,

Andre

[1] 1722-2016 - IEEE Standard for a Transport Protocol for Time-Sensitive Applications in Bridged Local Area Networks
[2] http://linuxptp.sourceforge.net
[3] https://patchwork.ozlabs.org/cover/826678/
[4] https://github.com/AVnu/libavtp
[5] http://mailman.alsa-project.org/pipermail/alsa-devel/2018-August/139494.html
[6] http://mailman.alsa-project.org/pipermail/alsa-devel/2018-September/140290.html
[7] https://github.com/aguedes/alsa-plugins

Andre Guedes (7):
aaf: Introduce plugin skeleton
aaf: Load configuration parameters
aaf: Implement Playback mode support
aaf: Prepare for Capture mode support
aaf: Implement Capture mode support
aaf: Implement dump() ioplug callback
aaf: Add support for direct read/write transfers

 Makefile.am     |    3 +
 aaf/Makefile.am |    9 +
 aaf/pcm_aaf.c   | 1197 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 configure.ac    |    9 +
 doc/aaf.txt     |  142 +++++++
 5 files changed, 1360 insertions(+)
 create mode 100644 aaf/Makefile.am
 create mode 100644 aaf/pcm_aaf.c
 create mode 100644 doc/aaf.txt

2.14.4