WM8281ECSSLASHR datasheet(168/392 Pages) CIRRUS

168 / 392 page

WM8281

168

Rev 4.0

The Segment Interval defines the repetition rate of the SLIMbus Slots allocated to consecutive data

samples for a given Data Channel. The Presence Rate (PR) is the nominal sample rate of the audio

path. The Segment Rate (determined by the Segment Interval value) must be equal to or greater than

the Presence Rate for a given data channel. The following constraints must be observed, when

configuring a SLIMbus channel:



If Pushed or Pulled Transport Protocol is selected, the Segment Rate must be greater than

the Presence Rate, to ensure that samples are not dropped as a result of clock drift.



If Isochronous Transport Protocol is selected, the Segment Rate must be equal to the

Presence Rate. Isochronous Transport Protocol should only be selected if the data source

is frequency-locked to the SLIMbus CLK (ie. the data source is synchronised to the

SLIMbus Framer device).

SLIMBUS CONTROL SEQUENCES

This section describes the messages and general protocol associated with most aspects of the

SLIMbus system.

Note that the SLIMbus specification permits some flexibility in Core Message support for different

components. See

“SLIMbus Interface Control” for details of which message(s) are supported on each

of the SLIMbus devices that are present on the WM8281.

DEVICE MANAGEMENT & CONFIGURATION

This section describes the SLIMbus messages associated with configuring all devices on the SLIMbus

interface.

When the SLIMbus interface starts up, it is required that one (and only one) of the components

provides the Manager and Framer Device functions. Other devices can request connection to the bus

after they have gained synchronisation.

The REPORT_PRESENT (DC, DCV) message may be issued by devices attempting to connect to

the bus. The payload of this message contains the Device Class (DC) and Device Class Version

(DCV) parameters, describing the type of device that is attempting to connect. This message may be

issued

autonomously

the

connecting

device,

else

response

REQUEST_SELF_ANNOUNCEMENT message from the Manager Device.

After positively acknowledging the REPORT_PRESENT message, the Manager Device will then issue

the ASSIGN_LOGICAL_ADDRESS (LA) message to allow the other device to connect to the bus.

The payload of this message contains the Logical Address (LA) parameter only; this is the unique

address by which the connected device will send and receive SLIMbus messages. The device is then

said to be ‘enumerated’.

Once a device has been successfully connected to the bus, the Logical Address (LA) parameter can

be changed at any time using the CHANGE_LOGICAL_ADDRESS (LA) message.

The RESET_DEVICE message commands an individual SLIMbus device to perform its reset

procedure. As part of the reset, all associated ports will be reset, and any associated Data Channels

will be cancelled. Note that, if the RESET_DEVICE command is issued to an Interface Device, it will

cause a Component Reset (ie. all Devices within the associated component are reset). Under a

Component Reset, every associated Device will release its Logical Address, and the Component will

become disconnected from the bus.

INFORMATION MANAGEMENT

A memory map of Information Elements is defined for each Device. This is arranged in 3 x 1kByte

blocks, comprising Core Information elements, Device Class-specific Information elements, and User

Information elements respectively, as described in the MIPI specification. Note that the contents of the

User Information portion for each WM8281 SLIMbus Device are reserved.

Read/Write access is implemented using the messages described below. Specific elements within the

Information Map are identified using the Element Code (EC) parameter. In the case of Read access, a

unique Transaction ID (TID) is assigned to each message relating to a particular read/write request.

The REQUEST_INFORMATION (TID, EC) message is used to instruct a device to respond with the

indicated information. The payload of this message contains the Transaction ID (TID) and the Element

Code (EC).

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