An Introduction to the Mobile Industry Processor Interface(MIPI)
Alliance Standard
Serial Low-power Inter-chip Media Bus(SLIMbus TM)
By
Kenneth Boyce
Technology Director
National Semiconductor Audio Products Group
NOTICE
SLIMbus TM is a trademark of the MIPI Alliance,Inc.
This article is a general overview and introduction to SLIMbus TM and does not provide a thorough explanation of SLIMbus TM.This article is not a substitute for any part of the SLIMbus TM Specification.For a complete description of operational capabilities for SLIMbus TM,please use the SLI
Mbus TM Specification
which is available to members of the MIPI Alliance,Inc.
c/o IEEE-ISTO
445Hoes Lane
Piscataway,NJ08854
About The MIPI Alliance
The Mobile Industry Processor Interface(MIPI)Alliance is a collaboration of mobile industry leaders with the objective to define and promote open standards for interfaces to mobile application processors. Through these open standards,the MIPI Alliance intends to speed deployment of new services to mobile users by establishing specifications for standard hardware and software interface
s to mobile application processors and encouraging the adoption of those standards throughout the industry value chain.The MIPI Alliance is intended to complement existing standards bodies with a focus on microprocessors, peripherals and software interfaces.
Introduction
The Serial Low-power Inter-chip Media Bus(SLIMbus TM)is a standard interface between baseband or application processors and peripheral components in mobile terminals.The SLIMbus TM specification was developed within the MIPI Alliance by a dedicated group of MIPI member companies:Austria Microsystems,Freescale Semiconductor,Infineon Technologies AG,Intel Corporation,Marvell Semiconductor,Motorola,National Semiconductor,Nokia,NXP Semiconductor,RF Microdevices, Sonion,Sony-Ericsson,STMicroelectronics N.V.,Synopsys,Texas Instruments,Toshiba,and Wolfson Microelectronics.
Excerpt from the MIPI ALLIANCE website():
“The Mobile Industry Processor Interface(MIPI)Alliance is an open membership organization that includes leading companies in the mobile industry that share the objective of defining and promoting open specifications for interfaces in mobile terminals.MIPI Specifications establish standards for har
dware and software interfaces between the processors and peripherals typically found in mobile terminal systems.By defining such standards and encouraging their adoption throughout the industry value chain,the MIPI Alliance intends to reduce fragmentation and improve interoperability among system components,benefiting the entire mobile industry.”SLIMbus TM development was driven by the increased demand for multimedia functions within mobile terminals and other portable entertainment devices,as well as the recognition that high quality digital audio is a major driver of unit growth and product differentiation.
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沼气池SLIMbus TM Features Highlights
A partial,but representative,listing of the features of SLIMbus TM is given below.
∙Audio,data,bus and Device control on a single bus
∙Reduced pin count for lower overall product cost
∙Support for multiple,high quality audio channels
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∙Multiple,concurrent sample rates on a single bus
∙Efficient,host-less,peer-to-peer generic data communication
∙Standardized Message set for improved software reuse and increased interoperability
∙Use of common digital audio clocks as well as established system clocks
∙Dynamic clock frequency changes for optimizing bus power consumption
SLIMbus TM addresses limitations of existing digital audio interfaces such as I2S and PCM(which are primarily point-to-point connections between single components and support only one or two digital audio channels)by providing a scalable multi-drop architecture supporting many components and digital audio channels on a single bus structure.
For even greater flexibility and simplicity,SLIMbus TM eliminates the need for a control bus such as I2C, SPI,microWire™,UART or GPIO pins on the digital audio components.Additionally,it may also reduce (or eliminate)instances of these bus structures on other types of low bandwidth components within the mobile terminal.
SLIMbus TM is implemented by a synchronous2-wire,flexible TDM frame structure and surrounding bus arbitration mechanisms and message structures,which taken together establish flexible and robust data connections between SLIMbus TM Devices.
Although optimized for the transport of constant-rate media streams,SLIMbus TM can transport various types of asynchronous data as well as control data.
SLIMbus TM Physical Description
Physically,SLIMbus TM consists of two terminals,the data line(DATA)and the clock line(CLK)which are used to interconnect multiple SLIMbus TM Devices.
SLIMbus TM uses a multidrop bus topology where all bus signals are common to all components on the bus.As such,all devices on the bus must use the same protocol for communication.This architecture was chosen as it significantly reduces bus interconnect wiring in any product using it,while at the same time allowing a multiplicity of devices and device types to be connected to the bus.
A multidrop connection requires that only one transmitter device communicate at any given time on the bus to one or more receivers.SLIMbus TM devices contend for the bus access through an arbitration procedure.
SLIMbus TM uses a Time Division Multiplexed(TDM)architecture which allows multiple receiver and t
ransmitter devices to reside on the bus and allows all devices to inter-communicate within allocated channels and time frames.SLIMbus TM supports both device to device communication as well as single device to multiple device broadcast communication.
SLIMbus TM is not designed for hot-swap capability since the intended use is completely within a client terminal such as a cellular phone.However,SLIMbus TM devices may dynamically“drop off”the bus and “reconnect”to the bus as dictated by system usage requirements using appropriate protocols outlined in the SLIMbus TM specification.
SLIMbus TM Devices and Device Classes
A SLIMbus TM Device is a logical implementation of a system function.
Devices in a Device Class category share certain characteristics and functions.SLIMbus TM Devices fall into Device Class definitions which specifies the minimum requirements for Device control information, Device behavior,data Transport Protocol support,and data storage necessary to implement a Device of that Device Class.
Requirements for all Device Classes are:
∙The Device Class code,identifying the type of Device
∙The version number of the Device Class
∙Transport support he number of Ports and required attributes,directionality, and Transport Protocols,etc.,that are supported by these Ports
∙Message support requirements,identifying which Messages in addition to Core Messages are supported by the Device.
∙Information support,identifying the Core Information Elements and associated codes that are supported by the Device.
矩阵键盘程序Operation requirements,identifying all other behavior that is important to the operation of a Device that belongs to that Device Class. There are four SLIMbus TM Device Classes defined at the release of Version 1.0of the SLIMbus TM specification:Manager,Framer,Interface,and Generic.These Device Classes permit complete SLIMbus TM systems to be designed and implemented without any additional Device Classes.However, the set of Device Classes is expandable if desired.When additional Device Classe
s are defined,those Device Class codes will be allocated by the MIPI Alliance.
Manager Device
A Manager Device is responsible for booting SLIMbus TM,and performs bus administration(enumeration of Components and Devices,bus configuration,and dynamic channel allocation).
In a typical SLIMbus TM system the Manager would be located in a baseband or application processor rather than in a peripheral component.
If a system contains two Managers,only one is allowed to be active at any given time.
Framer Device
The Framer delivers a clock signal on the CLK line to all SLIMbus TM Components,and also contains logic to transmit the Guide and Framing Channels(Framing Information)on the DATA line in order to establish the highest level TDM Frame Structure of the bus and communicate that information to other SLIMbus TM Devices for establishing synchronization.
The clock may be a high quality clock useful for audio decoding and DACs which may eliminate the need for additional clock generation within the system.
Interface Device
In each Component the Interface Device provides bus management services,controls the Frame Layer, monitors Message Protocols implemented by the Component,reports information about the status of the Component,and manages the Component reset so that a Component can properly sequence its Devices. Generic Device(Function)
A Generic Device is a Device other than a Manager,Framer,or Interface.A Generic Device is generally considered to be the device to provide certain application functionality such as,for example,conversion from digital audio to analog(DAC)and vice versa(ADC).For this reason,Generic Devices are labeled “Function Device”in block diagrams in this article.无人机首推北京天宇创通
The Generic Device Class is used if no other specific device class for the application functionality exists. As an example,if a Microphone Device Class existed you would not ordinarily use a Generic Device class definition for microphone functionality.
To implement a Functional SLIMbus TM Device also requires the use of a SLIMbus TM Interface Device,and the associated Enumeration and Logical Addresses(EA and LA),Information and Value Elements(IE and VE),and Ports(P)of each device,which are used to establish bus connections,control and status information flow,and digital audio(or other data)flow.
Figure1below is an example showing a partial section of an Interface Device and a partial section of a Function Device and associated elements.Further detail is shown in Figure2below.
Figure1:Partial Sections of SLIMbus TM Interface Device and Function Device
Device Information and Value Elements
Information Elements(IE)and Value Elements(VE)are data storage elements used to hold status, configuration or other important information needed by a Device.The data stored may be Boolean in nature,or may have many values,depending upon the type of Device.
These IE and VE elements effectively replace registers typically found behind conventional control interfaces such as I2C or SPI.
An Information Element is a specific piece of data that resides in a Device,and is available to other Devices via Messages.Categories of Information Elements are:
∙Core-Information Elements which are the same for all Devices of all Device Classes
∙Device Class-specific-Information Elements which are the same for all Devices of a particular Device Class,but which may be different for all Devices of a different Device Class ∙User-Information Elements which are specific to a particular product or product family
A Value Element provides a standardized method to read and update Device parameters.Unlike an Information Element,a Value Element can be set to a specific value using a specific Message for the purpose.
Device Addressing
SLIMbus TM uses a48-bit Enumeration Addresses(EA)to uniquely identify Devices which can announce their presence on the bus.Each Device has an EA,which incorporates Manufacturer ID,Product Code, Device Index,and Instance Value for a Device.The Manufacturer ID code is supplied by the MIPI Alliance and uniquely identifies the manufacturer of the Device,similar to the manufacturer IDs used with PCI bus components.The Device Index code uniquely identifies multiple Devices within a single Component.The Instance Value code is for the case where multiple Devices of the same type or Class are attached to the bus.
After enumeration,the Active Manager assigns an8-bit Logical Address to Device(LA)which speeds up communication with devices,and is typically used until the bus is powered down.On the next bus power up,or if the Device drops off the bus and re-connects,it is entirely possible that a new Logical Address is assigned.
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