Audio, Low-Speed Data and Control

MIPI Alliance provides the Serial Low‑power Inter-chip Media Bus (SLIMbus®) and SoundWireSM, a pair of optimized interfaces with both complementary and unique features to integrate audio devices in a mobile or mobile-inspired system.

SLIMbus and SoundWire are designed to replace older legacy interface designs that present limitations to system designers, whether in terms of power, pin count, ease of integration and consistency of design from one system to another, or lack of scalability. Both interfaces can coexist in a system or with non-MIPI interfaces through bridging solutions.

Download the MIPI Specification Brief for audio interfaces

Complete Specifications are available to MIPI members only. For more information on joining MIPI, please go to Join MIPI.

MIPI Specification for Serial Low-power Inter-chip Media Bus (SLIMbus®)

The Low-Speed Multipoint Working Group (LML WG) first released a v1.0 Specification in 2007, providing several maintenance updates in the years since. Known as SLIMbus, the specification addresses very low power, low cost peripherals while being extensible to mid-speed devices. SLIMbus is a scalable and flexible interface designed to evolve with future market needs and demands, reducing fragmentation and consolidating multiple interface for control anddata onto a single two-wire bus.

The LML WG is committed to supporting the adoption of SLIMbus by designing new device classes, by helping the SLIMbus community to develop standardized methods to test and validate SLIMbus implementations and by generating comprehensive white papers on SLIMbus benefits and architectures.

Complete specifications are available to MIPI members only. For more information on joining MIPI, please go to Join MIPI.

Introduction

Demand for multimedia functions within mobile terminals is increasing. A key driver for unit growth and product differentiation is digital audio.

Commonly used digital audio interfaces in mobile terminals such as I2S and PCM are generally intended for point-to-point connection between an application processor and a single digital audio device. Typically, these interfaces only support one or two digital audio channels. As such, adding functions and digital audio channels to mobile terminals beyond those for voice communication and simple stereo music applications is very difficult without increasing the number of bus structures in the mobile terminal. Though scalable, just adding bus structures limits design flexibility and is costly in terms of pin count, package size, PCB layout area and power consumption.

In addition, numerous control bus structures such as I2C, SPI, microWire™, UART and GPIOs, typically reside in parallel to audio buses not only for audio device control, but handling the countless low bandwidth control tasks required for lighting, haptic feedback, temperature monitoring and power sequencing.

SLIMbusSM provides the mobile terminal industry a standard, robust, scalable, low-power, high-speed, cost-effective, two wire multi-drop interface that supports a wide range of digital audio and control solutions for mobile terminals.

SLIMbus effectively replaces many other digital audio buses such as PCM and I2S, as well as control buses such as I2C, SPI, or UART, in a mobile terminal by providing flexible and dynamic assignment of bus bandwidth between digital audio and non-audio control and data functions. SLIMbus is not backward compatible with any current digital audio bus or digital control.

Scope

SLIMbus interface protocols and commands are within the scope of this specification. Electrical specifications at the physical terminals of SLIMbus Devices, as well as a description of signal timing relationships, are also within the scope of this specification. Implementation details of the SLIMbus interface within an electronic device are not within the scope of this document.

Purpose

The purpose of this document is to specify a standard interface between baseband or application processors and peripheral components. Implementing the SLIMbus Specification greatly increases the flexibility for mobile terminal system designers to realize multiple products within a product line quickly, each with widely varying digital audio and user interface features, without the addition of multiple bus structures. SLIMbus reduces the time-to-market and design cost of mobile terminals by simplifying the interconnection of products from different manufacturers.

Summary of SLIMbus Features

A SLIMbus interface offers many benefits, including:

  • Audio, data, bus and Device control on a single bus
  • Reduced pin count for lower overall product cost
  • Support for more than ten Components at typical bus lengths and speeds
  • Support for multiple, high quality audio channels
  • Multiple, concurrent sample rates on a single bus
  • Efficient, host-less, peer-to-peer communication
  • Standardized Message set for improved software reuse and increased interoperability
  • Established framework for Device creation
  • Use of common digital audio clocks as well as established system clocks
  • Dynamic clock frequency changes for optimizing bus power consumption

MIPI Specification for SoundWireSM

More than 25 companies, from audio peripheral, electronic design automation, silicon vendors and OEMs, took part in developing MIPI SoundWire, currently scheduled for approval at the end of 2014. SoundWire can be implemented in small, very cost-sensitive audio peripherals such as amplifiers and mcrophones.

Introduction

The SoundWireSpecification describes an interface for transportingaudio and related data.

One SoundWire Master interface communicates with one or more SoundWire Slave interfaces using two signals that are common to all Devices on the SoundWire bus. An optional multi-lane extension uses extra signals to provide increased data bandwidth among subsets of the Devices on the SoundWire bus.

The SoundWire interface addresses a wide range of system scenarios where up to eleven Slave interfaces share the common bus, and where those Slaves contain anything from one single-channel audio Data Port up to fourteen 8-channel Data Ports (using multi-lane extension up to 8 lanes to provide sufficient bandwidth).

Scope

This Specification describes the SoundWire interface at several layers of abstraction, from the timing an electrical characteristics of the physical layer, through data encoding, Frame synchronization and control information up to payload transport and distribution to multiple payload channels. It includes the content and function of the Registers present in each of the SoundWire interfaces.

It does not define the application-level meaning of the data conveyed over the interface, such as the mapping between PCM audio channel data values and analogue audio signals.

Purpose

This Specification provides a technical definition of the SoundWire interface to address the needs of the following:

  • Component design and verification engineers implementing SoundWire Master, Slave and Monitor interfaces
  • System-level hardware and software engineers designing equipment in which components communicate via SoundWire interfaces
  • Test engineers working on components or systems with SoundWire interfaces

Summary of SoundWire Features

  • Transporting all of payload data channels, control information, and setup commands over a single two-pin interface
  • Clock scaling and optional multiple data lanes to give wide flexibility in data rate to match system requirements
  • Lower clock frequency, and hence lower power consumption, by use of DDR data transmission
  • Handling up to 11 Slaves from a single Master interface
  • Support for direct Slave to Slave data transport
  • Support for multiple payload transport mechanisms, including both isochronous and asynchronous audio streams
  • Flexibility in size and complexity of payload ports, including both PCM and PDM audio streams
  • Very low latency for high sample rate audio stream payloads (such as PDM)
  • Device status monitoring, including interrupt-style alerts to the Master
  • Support for system-level power saving by temporarily stopping the clock and waking up in response to in-band signaling from Slaves
  • Extensibility for implementation-defined features
  • Support for Built-In Self-Test for component and system testing
  • Support for debug and monitoring tools during system development.