CS47L35 datasheet(125/300 Pages) CIRRUS

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DS1085F3

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CS47L35

4.9 SLIMbus Control Sequences

The segment interval gives rise to segment windows for each data channel, aligned to the start of every superframe. The

segment window boundaries define the times within which each new data sample must be buffered, ready for

transmission—adherence to these fixed boundaries allows slot allocations to be moved within a segment window, without

altering the signal latency. The segment interval may be either shorter or longer than the frame length, but there is always

an integer number of segment windows per superframe.

The TP defines the flow control or handshaking method used by the ports associated with a data channel. The applicable

flow control modes depend on the relationship between the audio sample rate (flow rate) and the SLIMbus CLK frequency.

If the two rates are synchronized and integer related, no flow control is needed. In other cases, the flow may be regulated

by the use of a presence bit, which can be set by the source device (pushed protocol), or by the sink device (pulled

protocol).

The data-channel structure is defined in terms of the TP, SD, and SL parameters.

The data-channel content definition includes a presence rate (PR) parameter (describing the nominal sample rate for the

audio channel) and a frequency locked (FL) bit (identifying whether the data source is synchronized to the SLIMbus CLK).

The data length (DL) parameter defines the size of each data sample (number of slots). The auxiliary bits format (AF) and

data type (DT) parameters provide support for non-PCM encoded data channels; the channel link (CL) parameter is an

indicator that channel CN is related to the previous channel, CN-1.

For a given root frequency and clock gear, the SL and SD parameters define the amount of SLIMbus bandwidth that is

allocated to a given data channel. The minimum bandwidth requirements of a data channel are represented by the

presence rate (PR) and data length (DL) parameters. The allocated SLIMbus bandwidth must be equal to or greater than

the bandwidth of the data to be transferred.

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 be selected only if the data source is frequency locked to the SLIMbus CLK (i.e., the data

source is synchronized to the SLIMbus framer device).

4.9 SLIMbus Control Sequences

This section describes the messages and general protocol associated with the SLIMbus system.

Note: The SLIMbus specification permits flexibility in core message support for different components. See Section 4.10

for details regarding which messages are supported on each of the SLIMbus devices present on the CS47L35.

4.9.1

Device Management and 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 only one component provides the manager and framer device

functions. Other devices can request connection to the bus after they have gained synchronization.

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 by the connecting device, or else in response

to a REQUEST_SELF_ANNOUNCEMENT message from the manager device.

After positively acknowledging the REPORT_PRESENT message, the manager device then issues 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 sends and receives

SLIMbus messages. The device is then said to be enumerated.

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