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Streamlining interconnections for compact designs

Posted: 24 Sep 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Internet of Things? MIPI UniPro? M-PHY? MIPI Alliance? MIPI?

Engineers must grapple with numerous concurrent trends as they strive to craft innovative designs for mobile and mobile-influenced devices. Miniaturisation of silicon chips, gigabit-per-second data speeds, the Internet of Things and new interest in modular architectures, for example, are opening up compelling opportunities to improve functionalities and create new design efficiencies.

One challenge associated with these trends is the need to simplify the electronic interfaces that interconnect device chipsets and peripheral components. I'd like to use this article to discuss MIPI UniPro (Unified Protocol), a versatile transport layer that can address these important needs. MIPI UniPro simplifies interconnections for smartphones, tablets, laptops, cameras and multimedia devices, as well as the various types of smart watches, health monitors and other innovative products that are entering the market as part of the Internet of Things.

MIPI UniPro: Its purpose and applications in the market
MIPI UniPro, offered by MIPI Alliance, specifies a transport layer protocol stack for switched packet transfer. Implemented on top of the MIPI M-PHY physical layer, it forms the MIPI UniPort-M interface.

As its name indicates, MIPI UniPro is a unified protocol. It is not dedicated to specific applications, as protocols often are. It was designed from the outset as a general-purpose, lightweight protocol with excellent protocol efficiency that is dedicated to mobile devices. It does not suffer from the heavy overhead imposed by other well-known legacy protocols that have been developed for the PC industry, where power consumption is not always a concern. It can be used as a stand-alone interface for inter-processor communications (IPC) or as a building block for multimedia interfaces. It can be used with other MIPI or non-MIPI application layer protocols.

MIPI UniPro's and MIPI M-PHY's versatility are illustrated by the types of organisations that have adopted the specifications. The JEDEC organisation uses UniPort-M to provide the basis for its Universal Flash Storage (UFS) specification. Google is using UniPort-M to connect the modules that will make up its Project Ara smartphone platform. The MIPI Camera Serial Interface (MIPI CSI-3) uses the UniPort-M interface to connect cameras with the application processor.

The specification's history
MIPI UniPro has been available since 2007. The current release, v1.6, has been available since September 2013.

The role for MIPI UniPro in the industry began in 2004, when MIPI Alliance formed the MIPI UniPro Working Group to develop an interoperable interface that could meet a wide range of needs. The group's objectives were to support a variety of component types and data traffic in a single protocol stack; reduce and standardise the number of physical links between devices and thus pave the way for design modularity to shorten the design and manufacturing cycle of new phones; simplify system integration of key components; and ensure backward compatibility of all versions to future-proof the specification.

Highlights of key technical features with use case scenarios
Following are summaries of some of the technical features that enable MIPI UniPort-M to meet so many diverse interface needs.

Versatile physical link: MIPI UniPort-M makes it possible to use multiple logical channels on one physical link. A so-called CPort serves as a bi-directional application entry and exit point for each of the up to 2047 logical channels. Application messages on each logical channel are fragmented, dispatched with a UniPro frame header and footer, and travel time-multiplexed through the physical M-PHY channel, as illustrated in figure 1.

Figure 1: Example of a UniPro Frame Multiplex.

Therefore a single physical channel can be used to support the logic needed to interface multiple applications, such as display, audio, control, storage, and others. Alternatively, a single application can share a bi-directional CPort channel for multiple purposes: For example, a display device can use a CPort channel to connect to the display and use the reverse channel for touch screen data (figure 2).

Figure 2: Using MIPI UniPort-M as a common transport channel into a media module.

Scaling link speeds and changing power modes
MIPI UniPort-M provides scalable link speeds and the ability to adjust these dynamically to optimise performance while managing power consumption. A bi-directional UniPort-M link is characterized mainly by its mode of operation, its speed gear, and the number of lanes in use. The SLOW MODE is optimised for low power transfer; lanes are typically unterminated, and seven different speed gears are supported, ranging from 3Mbps to 576Mbps per lane. In FAST MODE, three different speed gears are supported starting from 1.5Gbps per lane, doubling with every gear and reaching to 6Gbps per lane. Up to four lanes in parallel are supported on outbound or inbound link offering asymmetric settings in both directions. The SLOW and FAST modes can be combined with the AUTO feature, which controls M-PHY BURST closure and thus link power in the case of gaps in data traffic. In the complete absence of data traffic, HIBERNATE mode drives the entire link into ultra-low power consumption.

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