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ALSA Topology v1 (tools/topology/topology1)

This directory contains the source files and m4 macros used to generate version 1 of the ALSA topology binary files (.tplg) for Sound Open Firmware.

Overview

Topology v1 relies heavily on the m4 macro processor to handle the complexity and reusability of DSP graph definitions. Because raw ALSA configuration files for complex audio routing can become extremely verbose and repetitive, SOF uses m4 to define logical blocks (like DAIs, SSPs, pipelines, and volume controls) that can be easily instantiated and connected.

Structure

The core generation components include:

  • m4/: This directory contains the foundational macro definitions. These macros define how base elements like widgets (e.g., PGA, Mixer, SRC), pipelines, and routing paths are constructed in the ALSA .conf format.
  • common/: Contains shared components and standard pipeline definitions that are reused across multiple different hardware platforms.
  • platform/: Contains macros and configurations specific to individual hardware architectures (e.g., Intel cAVS, IMX).
  • Platform .m4 files: At the root of topology1, there are numerous .m4 files (e.g., sof-cavs-nocodec.m4, sof-imx8-wm8960.m4). These are the top-level files that instantiate the macros to build a complete topology graph for a specific board or hardware configuration.

Component Assembly

Building a topology in v1 is essentially a process of calling nested m4 macros to piece together the DSP pipeline. Here's how the ingredients combine:

  1. Base Macros (m4/): Define the raw ALSA syntax for things like a single PGA volume control or a DAI link.
  2. Pipelines (common/): Define a logical sequence of base widgets. For example, a "Playback Pipeline" macro might chain together a Host PCM, a Buffer, a Volume Control (PGA), and an output Buffer.
  3. Top-Level File (*.m4): Instantiates the pipelines, defines the physical DAI hardware connections, and sets up routing lines between the pipelines and the DAIs.
graph TD
    subgraph "Base Ingredients (m4/)"
        A[Widget: PCM]
        B[Widget: PGA Volume]
        C[Widget: DAI]
        D[Widget: Mixer]
    end

    subgraph "Recipes (common/ & platform/)"
        P1[Playback Pipeline]
        P1 -.->|Includes| A
        P1 -.->|Includes| B

        P2[Capture Pipeline]
        P2 -.->|Includes| D
        P2 -.->|Includes| C
    end

    subgraph "The Meal (sof-board.m4)"
        Top[Top-Level Topology]
        Top ==>|Instantiates| P1
        Top ==>|Instantiates| P2
        Top ==>|Defines| Routes[Audio Routes]
        Routes -.->|Connects Pipeline to DAI| Top
    end
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Build Flow

Architecture Diagram

flowchart TD
    m4_core(["m4/ (Core Macros)"]) -.-> m4_plat(["platform/ (Platform Macros)"])
    m4_comp(["common/ (Shared Components)"]) -.-> m4_plat

    m4_plat -.-> m4_top(["sof-*.m4 (Top-level Platform File)"])

    m4_top -->|"m4 processor"| conf["ALSA .conf Output"]

    conf -->|"alsatplg"| tplg["ALSA .tplg Binary"]
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When the SOF build system compiles a v1 topology:

  1. The m4 processor takes a top-level platform .m4 file.
  2. It expands all the macros defined in m4/, common/, and platform/.
  3. The output is a raw ALSA .conf text file.
  4. The alsatplg compiler parses this .conf file and compiles it into the final .tplg binary format loaded by the kernel.

Build Instructions

Topologies are built automatically as part of the standard SOF CMake build process. To explicitly build all topologies (including v1):

# From your build directory:
make topologies1
# OR
cmake --build . --target topologies1