Introduction to the SOF Project

Sound Open Firmware (SOF) is an open source audio Digital Signal Processing (DSP) firmware infrastructure and SDK. SOF provides infrastructure, real-time control pieces, and audio drivers as a community project. The project is governed by the Sound Open Firmware Technical Steering Committee (TSC) who are prominent and active developers from the community. SOF is developed in public and hosted on the github platform.

The firmware and SDK are intended for developers who are interested in audio or signal processing on modern DSPs. SOF provides a framework where audio developers can create, test and tune.

  1. Audio processing pipelines and topologies.

  2. Audio processing components.

  3. DSP infrastructure and drivers.

  4. Host OS infrastructure and drivers.

SDK Overview

Figure 1 Example Equalizer pipeline with host OS control of EQ coefficients and pipeline volume.

Sound Open Firmware has a modular and generic codebase and can be ported to different DSP architectures or host platforms. See list of currently supported DSP architecures and supported platforms.

SDK Introduction and Overview

The Sound Open Firmware SDK is comprised of many ingredients that can be customised for use in the firmware/software development lifecycle. Customisation allows for a “best fit” development approach where the SDK can be optimised for a particular process or environment. Some SDK ingredients are optional whilst there can more than once choice for other ingredients as shown in the diagram below.

SDK Overview

Figure 2 SDK example configuration showing development flow for SOF on the Intel Apollolake platform running Linux OS. Note the choice of compiler toolchains and choice of optional DSP emulators.

SOF source code, tools and topologies

The firmware, tools and topologies all exist in the main SOF git repository and at a high level it contains.

  1. Firmware - written in C with some architecture-specific assembler; it does not link to external dependencies.

  2. Test Bench - allows firmware components and pipelines to run on developers host PC.

  3. Image Tools - C tools for converting ELF files to binary firmware images that can run on HW.

  4. Debug Tools - Scripts and tools that can be used to debug firmware.

  5. Trace Tools - Text based tools that can display tracing data from firmware.

  6. Tuning Tools - Matlab/Octave scripts that can be used to create tuning coefficients for audio components.

  7. Runtime Tools - Command line applications that can be used to exchange data with running firmware.

  8. Topologies - Real and example topologies showing construction of simple and complex audio processing pipelines.

Host OS Drivers

SOF can be configured and controlled by a host OS driver or can optionally run as a stand alone firmware. SOF host drivers currently support the Linux OS today.

The SOF driver has a modular stack based architecture that is dual licensed BSD & GPL code allowing it to be ported to other OSes and RTOSes.

The host driver is responsible for :-

  1. Loading firmware from host file system into DSP memories and booting.

  2. Loading topologies from host file system into DSP.

  3. Exposing audio control devices to applications.

  4. Exposing audio data endpoints to applications.

  5. Managing IPC communication between host and DSP.

  6. Abstraction of host side DSP hardware to common API operations.

The Linux SOF ALSA/ASoC driver is upstream in Linux v5.2 onwards.

Firmware Toolchain

GNU GCC can be used as a free SOF compiler alongside proprietary DSP vendor compilers. The choice of compiler is up to the user depending on features and budget. GCC complier is open source.

DSP Emulator

Qemu can be used to provide a functional emulator to simultaneously trace and debug driver and DSP firmware code. Proprietary emulators are also available.

Emulation is also used within SOF CI for feature validation prior to merging new code.

General FAQ

What license does the firmware use?

The firmware is released using a standard BSD 3-clause license with some files released under MIT.

Do I need to open source my firmware code changes?

No. The firmware BSD and MIT licensed code means you can keep code changes private. Patches are always welcomed if you do decide to open source work.

What license does the host driver use?

Most of the host driver code is dual licensed BSD or GLPLv2 only (user’s choice). The part of the driver that is GPLv2 only is the Linux integration layer at the top of the driver stack

Do I need to open source my driver code changes?

No, for the bottom two layers of the driver stack. i.e. if you are porting the driver to another OS, these changes can be kept private. Please note that the driver GPL source files are all Linux specific and should not be ported to another OS anyway.

How can I get involved?

The best way to get involved is via github, there is also a low volume mailing list here http://alsa-project.org/mailman/listinfo/sound-open-firmware

What is the development model?

Sound Open Firmware is entirely developed on github. Patches via a Pull Request are reviewed, discussed and tested by CI before being merged. The intended release cadence will likely be every 6 - 8 weeks. There will be a stable release tagged after passing QA then development will continue for the next release.

Who is working on Sound Open Firmware?

Professional developers from a number of companies (please check the git logs if you want to know) with some hobbyist developers too.

How do I add support for host architecture X?

Please see the SOF architecture pages.

How do I add support for host platform X?

Adding a new host platform is a lot simpler than adding a new DSP architecture. A new host platform consists of adding a new src/platform/ directory, together with mappings for memory, IRQs, GPIOs and peripheral devices in the DSP memory space. New drivers may also have to be added (e.g. for DMA, I2S) to the drivers directory.

How do I port to other OSes?

Please see the SOF host architecture page.

What audio components are supported?

Sound Open Firmware now supports a small library of free and open source components that are distrubuted alongside the source code. SOF can also support proprietary audio processing components providing they are wrapped to use the SOF component API. Please see the audio components page for a list of the open source components and thier capablilities.

How do I create my own pipelines?

Pipelines are currently defined using the M4 macro processing language. The M4 topology is then preprocessed to the alsaconf format before being compiled into a binary. An Eclipse based GUI for pipeline construction is currently in development.

Today both static (built in) and dynamic (loaded at runtime) pipelines are supported in upstream.

Can I add my own media encoder/decoders?

Yes.

Can I add non-audio functions?

Yes, the instruction sets used by DSPs are also good at non audio processing tasks too. e.g. low power sensor signal processing. Providing your DSP has physical IO ports to connect other non audio devices then it’s possible to process data from these devices too.