UniPro - AbsoluteAstronomy.com

UniPro^SM is a high-speed interface technology for interconnecting integrated circuits in mobile phones or comparable products. The various versions of the UniPro standard are created within the MIPI^® Alliance

Mobile Industry Processor Interface

The Mobile Industry Processor Interface 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 inside mobile terminals.Formed in July 2003 by Intel, Nokia, Samsung,...

.

The UniPro technology and associated physical layer

Physical layer

The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....

s aim to provide high-speed data communication (gigabits/second), low-power operation (low swing signaling, standby modes), low pin count (serial signaling, multiplexing), small silicon area (small packet sizes), data reliability (differential signaling

Differential signaling

Differential signaling is a method of transmitting information electrically by means of two complementary signals sent on two separate wires. The technique can be used for both analog signaling, as in some audio systems, and digital signaling, as in RS-422, RS-485, Ethernet , PCI Express and USB...

, error recovery) and robustness (proven networking concepts, including congestion management).

UniPro versions 1.0, 1.1 and 1.4 concentrate on enabling high-speed point to point communication between chips in mobile phones. UniPro has provisions for supporting networks consisting of up to 128 UniPro devices (integrated circuit, modules, etc.). Network features are planned in future UniPro releases. In such a networked environment, pairs of UniPro devices are interconnected via so-called links while data packets are routed toward their destination by UniPro switches. These switches are analogous to the routers used in wired LAN based on gigabit Ethernet. But unlike a LAN, the UniPro technology was designed to connect chips within a mobile terminal, rather than to connect computers within a building.

History and aims

The initiative to develop the UniPro standard came forth out of a pair of research projects at respectively Nokia Research Center and Philips Research. Both teams independently arrived at the conclusion that the complexity of mobile systems could be reduced by splitting the system design into well-defined functional modules interconnected by a network.
The key assumptions here were thus that the networking paradigm gave modules well-structured, layered interfaces and that it was time to improve the system architecture of mobile systems to make their hardware- and software design more modular. In other words, the goals were to counteract the rising development costs, development risks and time-to-market impact of increasingly complex system integration.

In 2004, both companies jointly founded what is now MIPI

Mobile Industry Processor Interface

's UniPro Working Group. Such multi-company collaboration was considered essential to achieve interoperability between components from different component vendors and to achieve the necessary scale to drive the new technology.

The name of both the working group and the standard, UniPro, reflects the need to support a wide range of modules and wide range of data traffic using a single protocol stack. Although other connectivity technologies (SPI

Serial Peripheral Interface Bus

The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link standard named by Motorola that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select ...

, PCI

Peripheral Component Interconnect

Conventional PCI is a computer bus for attaching hardware devices in a computer...

, USB) exist which also support a wide range of applications, it should be noted that the inter-chip interfaces in the mobile device industry are still generally proprietary and very diverse. This situation thus differs significantly from the (in this respect more mature) computer industry.

The final draft of Version 1.1 of the UniPro specification was completed in July 2009. Its acknowledgements list 42 engineers from 15 companies and organizations: Arasan, Broadcom, Freescale, IEEE-ISTO, Infineon, Motorola, Nokia, NXP, Qualcomm, Research in Motion, ST-Ericsson, St. Petersburg University, Testronic Laboratories, Texas Instruments, and Toshiba. In January 2011, UniPro Version 1.4 was completed. Its main purpose is full support for a new Physical Layer: M-PHY including support for power modes change and peer device configuration. The UniPro v1.4 specification has been released together with a formal specification model (SDL).

To date, several vendors have announced the availability of UniPro IP blocks and various chip suppliers have created implementations that are at various phases of development. In the meantime, the MIPI UniPro Working Wroup is setting up a conformance test suite and is preparing future extensions of the technology (see UniPro Versions and Roadmap).

Main features

gigabit/s - serial technology with a number of bandwidth scaling options
generic - can be used for a wide range of applications and data traffic types
scalable - from individual links to a network with up to 128 UniPro devices
low-power - optimized for small battery-powered systems
reliability - data errors detected and correctable via retransmission
hardware friendly - can be implemented entirely in hardware where needed
software friendly - similar concepts to familiar network technologies
bandwidth utilization - provides features to manage congestion and control arbitration
shareable - different traffic types and UniPro devices can share pins and wires
testable - since version 1.1, UniPro mandates features to facilitate automated conformance testing

Layered architecture

UniPro associated with its underlying PHY layer is a layered protocol stack that covers layers L1 to L4 of the OSI Reference Model

OSI model

The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...

for networking. UniPro introduces an extra layer L1.5 between L1 and L2 which can be regarded as a sub-layer of OSI's layer L1.

Multiple applications

UniPro's strict layering enables it to be used for a wide range of applications:

UFS: Universal Flash Storage. Next generation mass storage devices specified by JEDEC with a support for data throughput of up to 300MB/sec, in the first generation, and support command queuing features to raise the random read/write speed.
CSI-3: 3^rd generation MIPI Camera Serial Interface features a scalable high bandwidth interface, a guaranteed data transmission and a command set for basic component initialization and configuration.
GBT: MIPI Gigabit Trace. A network independent protocol for transporting trace data over high-speed interfaces such as UniPort-M or USB3.0.
DSI-2: 2^nd generation MIPI Display Serial Interface.
PIE: Processor Emulation Interface. This application protocol conveys traditional memory-based read/write transactions as found on processor busses. Data streaming applications (e.g. multimedia traffic), command/response-type protocols (e.g. for control), and tunneling of popular protocols from other domains (e.g. TCP/IP) are also supported and specifically encouraged because they tend to increase system-level modularity and interoperability due to their higher abstraction level.
General purpose extension interface to connect peripheral devices such as graphic accelerators etc…

Alternative physical layers

UniPro's layered architecture also allows it to support multiple physical layer (L1, PHY) technologies even within a single network. This is analogous to TCP/IP which can run on a wide range of lower-layer technologies. In the case of UniPro, two PHY technologies are supported for off-chip use.

UniPorts

These PHY technologies are covered in separate MIPI specifications (which are referenced by the UniPro specification. Note that the term UniPort is used to represent the actual port on a chip which conforms to the UniPro specification for its upper layers (L1.5 to 4) and a MIPI PHY specification for L1. As there are two PHY technologies, these are respectively known as UniPort-D (UniPro with D-PHY) and UniPort-M (UniPro with M-PHY).

Phased roadmap

The UniPro 1.0 specification was approved by the MIPI Board of Directors on January 14, 2008. UniPro 1.1, that was completed in July 2009, aims to improve readability, provides reference model (in SDL

Specification and Description Language

Specification and Description Language is a specification language targeted at the unambiguous specification and description of the behaviour of reactive and distributed systems.- Overview :It is defined by the ITU-T...

) for two of the four UniPro protocol layers, and provides features to facilitate automated conformance testing.

The architects designing UniPro intended from the start to release the technology as a step-wise roadmap with backward compatibility. UniPro 1.1 is designed to be fully backwards compatible with UniPro 1.0.
The UniPro 1.40.00 (current 1.4 DRAFT) specification is undergoing adoption process by MIPI. The main purpose of UniPro 1.4 is to support an additional physical layer, the M-PHY. Furthermore, UniPort-M features local and remote control of a peer UniPro device that can be used for example to control various supported power modes of the link.
Planned roadmap steps beyond 1.4 aim to provide specifications for network-capable endpoint and network switch devices.

Scope and applicability

UniPro and its underlying physical layer were designed to support low power operation needed for battery-operated systems. These features range from power-efficient high-speed operation to added low-power modes during idle or low bandwidth periods on the network. Actual power behavior is, however, highly dependent on system design choices and interface implementation.

The UniPro protocol can support a wide range of applications and associated traffic types. Example chip-to-chip interfaces encountered in mobile systems:

Processor trace: 4 Gbps
Mass storage file transfer : 3 Gbps
12M pixel camera @30fps : 4.5Gbps
HD display 1080p@60fps : 3 Gbps

Note that such applications require an application protocol layer on top of UniPro to define the structure and semantics of the byte streams transported by UniPro. These can be done by simply porting existing data formats (e.g. tracing, pixel streams, IP packets), introducing new proprietary formats (e.g. chip-specific software drivers) or defining new industry standards (e.g. UFS for memory-like transactions).

Applications which are currently believed to be less suitable for UniPro are:

low-bandwidth control - unless multiplexed with other traffic (concern: UniPro complexity is much higher than e.g. I2C)
high-quality audio samples (concerns: UniPro does not distribute a shared clock to all devices; UniPro complexity compared to e.g. SLIMbus
SLIMbus
The Serial Low-power Inter-chip Media Bus is a standard interface between baseband or application processors and peripheral components in mobile terminals. It was developed within the MIPI® Alliance, ARM, Nokia, STMicroelectronics and Texas Instruments...

or I2S
I²S
I2S, also known as Inter-IC Sound, Integrated Interchip Sound, or IIS, is an electrical serial bus interface standard used for connecting digital audio devices together. It is most commonly used to carry PCM information between the CD transport and the DAC in a CD player...

)
interfaces to dynamic memory (concern: latency for processor instruction/data fetch)

Versions and roadmap

Version	Text freeze	Formal release	Description
UniPro 0.80.00	6 September 2006	26 February 2007	Technology preview of UniPro 1.0
UniPro 1.00.00	25 August 2007	14 January 2008	Limited changes compared to UniPro 1.0. All the basics for a chip-to-chip link via the D-PHY
UniPro 1.10.00	29 July 2009	22 January 2010	"Hardened": formal reference models for 2 protocol layers; readability and testability improvements
UniPro 1.40.00	31 January 2011	28 April 2011	"M-PHY": support for a new physical layer technology. Formal reference model for the whole stack. Peer Configuration. Versioning.
future releases	t.b.d.	t.b.d.	"Endpoint": fully networkable endpoint including inband configuration protocol. "Switches": network switches. Sharing of the link between several applications. Dynamic Connection Management. Hot Plugging. Security features. Real Time Traffic Class.

Protocol stack architecture

The UniPro protocol stack follows the classical OSI reference architecture (ref). For practical reasons, OSI's Physical Layer is split into two sub-layers: Layer 1 (the actual physical layer) and Layer 1.5 (the PHY Adapter layer) which abstracts from differences between alternative Layer 1 technologies.

*UniPro protocol stack (this color coding is a long-standing UniPro tradition)*
Layer #		Layer name	Functionality	Data unit name
LA		Application	Payload and transaction semantics	Message
DME
	Layer 4	Transport	Ports, multiplexing, flow control Flow control In data communications, flow control is the process of managing the pacing of data transmission between two nodes to prevent a fast sender from outrunning a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with...	Segment
	Layer 3	Network	Addressing, routing	Packet
	Layer 2	Data link	Single-hop reliability and priority-based arbitration	Frame
	Layer 1.5	PHY adapter	Physical layer abstraction and multi-lane support	UniPro symbol
Layer 1		Physical layer (PHY)	Signaling, clocking, line encoding, power modes	PHY symbol

The UniPro specification itself covers Layers 1.5, 2, 3, 4 and the DME (Device Management Entity). The Application Layer (LA) is out of scope because different uses of UniPro will require different LA protocols. The Physical Layer (L1) is covered in separate MIPI specifications in order to allow the PHY to be reused by other (less generic) protocols if needed.

Note that OSI Layers 5 (Session) and 6 (Presentation) are, where applicable, counted as part of the Application Layer.

The various layers and their features are described in more detail on a dedicated Wikipedia page

UniPro protocol stack

In mobile-telephone technology, the UniPro protocol stack follows the architecture of the classical OSI Reference Model. In UniPro, the OSI Physical Layer is split into two sublayers: Layer 1 and Layer 1.5 which abstracts from differences between alternative Layer 1 technologies...

UniPro and system integration

UniPro is specifically targeted by MIPI to simplify the creation of increasingly complex products. This implies a relatively long-term vision about future handset architectures composed of modular subsystems interconnected via stable, standardized, but flexible network interfaces. It also implies a relatively long-term vision about the expected or desired structure of the mobile handset industry, whereby components can readily interoperate and components from competing suppliers are to some degree plug-compatible.

Similar architectures have emerged in other domains (e.g. automotive networks, largely standardized PC architectures, IT industry around the Internet protocols) for similar reasons of interoperability and economy of scale. It is nevertheless too early to predict how rapidly UniPro will be adopted by the mobile phone industry.

High bandwidth and costs

High speed interconnects like UniPro, USB or PCI Express

PCI Express

PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...

typically cost more than low speed interconnects (e.g. I2C, SPI

Serial Peripheral Interface Bus

or simple CMOS

CMOS

Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...

interfaces). This is for example because of the silicon area occupied by the required mixed-signal circuitry (Layer 1), as well as due to the complexity and buffer space required to automatically correct bit errors. UniPro's cost and complexity may thus be an issue for certain low bandwidth UniPro devices.

Note that UniPro 1.1 provides a new option to reduce buffering costs in basic devices which do not require dual priority levels for user data. Similarly the M-PHY specification plans to provide another cost-down option by allowing medium-speed UniPro devices to implement only a medium-speed subset of the M-PHY.

Adoption rate

As Metcalfe postulated, the value of a network technology scales with the square of the number of devices which use that technology. This makes any new cross-vendor interconnect technology only as valuable as the commitment of its proponents and the resulting likelihood that the technology will become self-sustaining. Although UniPro is backed by a number of major companies (including market leader Nokia), it will take a few more years before it is clear whether or not the technology becomes successful. Although the UniPro incubation time is more or less in line with comparable technologies (USB, Internet Protocol

Internet Protocol

The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...

, Bluetooth

Bluetooth

Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...

, in-vehicle networks), adoption rate is presumed to be main concern about the technology - especially because the mobile industry has virtually no track record on hardware standards which pertain to the internals of the product.

Availability of application protocols

Interoperability requires more than just alignment between the peer UniPro devices on protocol layer L1-L4: it also means aligning on more application-specific data formats, commands and their meaning, and other protocol elements. This is a known intrinsically unsolvable problem in all design methodologies: you can agree on standard and reusable "plumbing" (lower hardware/software/network layers), but that doesn't automatically get you alignment on the detailed semantics of even a trivial command like ChangeVolume(value) or the format of a media stream.

Practical approaches thus call for a mix of several approaches:

If the previous generation interconnect worked, there was some kind of solution. Consider reusing/tunneling/porting it with minimal changes.
There are many reusable application-specific industry standards (like commands to control a radio, audio formats, MPEG).
Tunnel major technologies over UniPro. If you interact with the IP world
Internet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...

, it is sensible to provide IP-over-UniPro.
Use application-specific software drivers. This only works for limited data rates and pushes the interoperability problem into an internal software interoperability problem, but is a well understood approach.
Turn existing software interfaces into protocols. In some cases the transformation can be simple or even automated if the original APIs have the right architecture.

Licensing

The Membership Agreement of the MIPI Alliance specifies the licensing conditions for MIPI specifications for member companies. Royalty-free licensing conditions apply within the main target domain of the MIPI Alliance, mobile phones and their peripherals, whereas RAND licensing conditions

Reasonable and Non Discriminatory Licensing

Reasonable and non-discriminatory licensing is a type of licensing typically used during standardization processes. When joining a standardization body, companies normally agree that if they receive any patents on technologies which become essential to the standard they agree to allow other...

apply in all other domains.

External links

www.MIPI.org - MIPI Alliance (document access requires an account)
UniPro testing program - conformance and interoperability testing
"Mobile chip interface gets real" - EE Times 2006 overview of MIPI status
"JEDEC announces standard for flash storage" - EE Times 2011

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.