CS47L85 datasheet(191/370 Pages) CIRRUS

191 / 370 page

CS47L85

Rev 4.3

191

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.

The Message Channel is allocated all of the Control space not used by the Framing Information or the Guide Channel. The

Message Channel enables SLIMbus devices to communicate with each other, using a priority-based mechanism defined in

the MIPI specification.

Messages may be broadcast to all devices on the bus, or can be addressed to specific devices using their allocated Logical

Address (LA) or Enumeration Address (EA). Note that, device-specific messages are directed to a particular device (i.e.,

Manager, Framer, Interface or Generic) within a component on the bus.

CS47L85 Datasheet(PDF) 191 Page - Cirrus Logic

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