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

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.

Fig. 1: Scope of SLIMbus in a Mobile System

 

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