ASoC

ASoC, or ALSA System on Chip, is a Linux kernel subsystem that provides audio support for system-on-chip (SoC) hardware. It extends the ALSA framework with a modular, topology-based model that connects digital audio interfaces on the processor (CPU DAIs) to external or on-chip audio codecs (codec DAIs). The goal is to enable flexible, scalable audio designs across diverse SoCs without hard-coding each platform.

Key concepts include CPU DAI and Codec DAI objects, DAI links that define the connections between a CPU DAI and a codec, and the snd_soc_card (machine driver) that describes the overall sound card topology for a given board. The framework also includes the Dynamic Audio Power Management (DAPM) component, which manages the enabling and disabling of individual paths to save power.

How it works: ASoC drivers implement or expose CPU DAI and Codec DAI drivers and declare their interconnections via dai_link structures. A machine (card) driver binds these components together, exposes the PCM interfaces to userspace through ALSA, and configures routing, formats, and clocking. The runtime graph can be adjusted to support different sampling rates, bit depths, and routing changes.

Impact: ASoC is the common approach for audio on Linux in embedded systems, enabling support for a wide range of SoCs and codecs through a shared, interoperable API. It is maintained as part of the Linux kernel’s ALSA subsystem and has broad vendor adoption.