SoundWire Interface: Protocol Basics and Advantages

This page covers SoundWire interface protocol basics and its benefits/advantages.

Introduction: The initial version of SoundWire was published in 2014 by the MIPI Alliance group of companies. The latest version is SoundWire V1.2.1, published in June 2022.

What is SoundWire Protocol?

SoundWire is an audio interface used in mobile phones, PCs, tablets, wearables, and other devices. It serves as a command/control protocol, utilizing 2 pins and offering a multi-drop interface using DATA and CLOCK lines.

Each frame of the SoundWire protocol can transmit a read or write command. It doesn’t require control interfaces like those used in I2S/I2C. This audio architecture supports up to 11 slave devices with each master.

The devices can be interfaced in different topologies such as basic system stereo I/O, daisy chain, star, Multi-lane, bridge, multiple masters with function split/alternate partitioning, etc.

Features of SoundWire Interface

Here are the features of the SoundWire Interface developed by the MIPI Alliance:

• 2 pin Data and Clock, 1.2V or 1.8V
• Dual data rate: Sampled on each edge, NRZI encoding
• Clocking up to 12.288 MHz, Clock stop
• Frame length (adjustable)
• Transports frames with PCM (Pulse Code Modulation) and PDM (Pulse Density Modulation) formats
• Isochronous and asynchronous mode
• Bulk transfer capability
• Event Signalling
• Enumerable bus (Software handles enumeration)
• Device types supported (Master, Slave, Monitor equipments) and supports 48 bit device ID

Functionalities and Roles of SoundWire Devices

The functionalities and roles of SoundWire devices are as follows:

• Master: Offers clock and synchronization between devices and the master. Provides bus management.
• Slaves: Available in the form of audio components which support wake-up capabilities and utilize in-band interrupts. Audio peripherals can include audio codecs, microphones, speakers, amplifiers, Bluetooth modules, FM radios, etc.
• Monitoring Equipments: Equipment can monitor, debug, and test data over the bus.

Soundwire interface can be used to connect application processor with multiple digital microphones and speakers.

The first wave of 5G smartphones will be equipped with Soundwire and its complement interface known as SLIMbus.

Benefits or Advantages of SoundWire

Following are the benefits or advantages of SoundWire:

• This interface simplifies the integration of multiple audio components across a wide range of platforms and devices.
• It supports low gate count hardware designs, which minimizes cost.
• It uses configurable frame sizes, which reduces transport overhead.
• The number of data channels and the number of data ports are configurable based on the bandwidth requirements of a peripheral. A data port supports 1 to 8 channels, and a slave supports up to 14 data ports.
• It offers superior power and performance compared to other audio connectivity standards.