WM8281ECSSLASHR datasheet(166/392 Pages) CIRRUS

166 / 392 page

WM8281

166

Rev 4.0

SLIMBUS INTERFACE

The SLIMbus protocol is highly configurable and adaptable, supporting multiple audio signal paths,

and mixed sample rates simultaneously. It also supports control messaging and associated

communications between devices.

SLIMBUS DEVICES

The SLIMbus components comprise different device classes (Manager, Framer, Interface, Generic).

Each component on the bus has an Interface Device, which provides bus management services for

the respective component. One or more components on the bus will provide Manager and Framer

Device functions; the Manager has the capabilities to administer the bus, whilst the Framer is

responsible for driving the CLK line and for driving the DATA required to establish the Frame

Structure on the bus. Note that only one Manager and one Framer Device will be active at any time.

The Framer function can be transferred between Devices when required. Generic Devices provide the

basic SLIMbus functionality for the associated Port(s), and for the Transport Protocol by which audio

signal paths are established on the bus.

SLIMBUS FRAME STRUCTURE

The SLIMbus bit stream is formatted within a defined structure of Cells, Slots, Subframes, Frames,

and Superframes:



A single data bit is known as a Cell



4 Cells make a Slot



192 Slots make a Frame



8 Frames make a Superframe

The bit stream structure is configurable to some extent, but the Superframe definition always

comprises 1536 slots. The transmitted/received bit rate is not fixed; it can be configured according to

system requirements, and can be changed dynamically without interruption to active audio paths.

The SLIMbus CLK frequency (also the bus bit rate) is defined by a Root Frequency (RF) and a Clock

Gear (CG). In the top Clock Gear (Gear 10), the CLK frequency is equal to the Root Frequency. Each

reduction in the Clock Gear halves the CLK frequency, and doubles the duration of the Superframe.

The SLIMbus bandwidth will typically comprise Control space (for bus messages, synchronisation

etc.) and Data space (for audio paths). The precise allocation is configurable, and can be entirely

Control space, if required.

The Subframe definition comprises the number of Slots per Subframe (6, 8, 24 or 32 Slots), and the

number of these Slots (per Subframe) allocated as Control space. The applicable combination of

Subframe length and Control space width are defined by the Subframe Mode (SM) parameter.

The SLIMbus Frame always comprises 192 Slots, regardless of the Subframe definition. A number of

Slots are allocated to Control space, as noted above; the remaining Slots are allocated to Data space.

Some of the Control space is required for Framing Information and for the Guide Channel (described

below); the remainder of the Control space are allocated to the Message Channel.

CONTROL SPACE

Framing Information is provided in Slots 0 and 96 of every Frame. Slot 0 contains a 4-bit

synchronisation code; Slot 96 contains the 32-bit Framing Information, transmitted 4 bits at a time

over the 8 Frames that make up the SLIMbus Superframe. The Clock Gear, Root Frequency,

Subframe configuration, along with some other parameters, are encoded within the Framing

Information.

The Guide Channel occupies two Slots within Frame 0. This provides the necessary information for a

SLIMbus component to acquire and verify the frame synchronisation. The Guide Channel occupies

the first two Control space Slots within the first Frame of the bit stream, excluding the Framing

Information Slots. Note that the exact Slot allocation will depend upon the applicable Subframe mode.

WM8281ECS/R Scheda tecnica(PDF) 166 Page - Cirrus Logic

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