Busses get slimmer

In response to the increased demand for multimedia functions within mobile terminals and other portable entertainment devices, the Mobile Industry Processor Interface (MIPI) Alliance has released the specification for a Serial Low-power Inter-chip Media Bus or SLIMbus.

SLIMbus is claimed to deliver significantly more audio capacity than existing I²S and other PCM digital audio busses. It also sports an independent messaging channel that offers faster communication capability than those busses too.

Offering up to 28Mb/sec of scalable bandwidth, SLIMbus will enable designers to mix multiple audio sample rates and control streams to meet varying system needs.

For instance, one moment a phone user may be listening to high quality 44.1kHz CD-audio, and then receive a call containing 8kHz voice samples. The control signalling for this transition, as well as the simultaneous transfer of the different sample rates, can be handled without dropped samples that can cause clicks or pops. Power conservation is optimised during these constantly changing system states by dynamic ‘gear-shifting’ that matches the bus speed with the bandwidth required.

‘Existing standards just didn’t deliver the functionality that new mobile products require, so we developed a standard that could meet those needs,’ said Christian Sternell, chair of the MIPI Working Group which developed SLIMbus. ‘We expect leading phone manufacturers to begin moving to SLIMbus as soon as component suppliers deliver products integrating the interface, beginning in 2008.’

At its core, SLIMbus is a multi-drop bus topology using CMOS I/O with framing based upon a Time Division Multiplexed structure. Devices arbitrate for access within the shared message channel, where a Manager allocates channels for guaranteed bandwidth. A Framer device is responsible for sourcing the bus clock along with basic framing information that allow all devices to synchronise and start communication with the Host.

The first implementations of the SLIMbus are likely to be seen in audio components within mobile devices, as size, cost and power benefits are most dramatic in these applications.