CS47L85 datasheet(192/370 Pages) CIRRUS

192 / 370 page

CS47L85

192

Rev 4.3

DATA SPACE

The Data space can be organised into a maximum of 256 Data Channels. Each Channel, identified by a unique Channel

Number (CN), is a stream of one or more contiguous Slots, organised in a consistent data structure that repeats at a fixed

interval.

A Data Channel is defined by its Segment Length (SL) (number of contiguous Slots allocated), Segment Interval (spacing

between the first Slots of successive Segments), and Segment Offset (the Slot Number of the first allocated Slot within the

Superframe). The Segment Interval and Segment Offset are collectively defined by a Segment Distribution (SD), by which

the SLIMbus Manager may configure (or re-configure) any Data Channel.

Each Segment may comprise TAG, AUX and DATA portions. Any of these portions may be 0-length; the exact composition

depends on the Transport Protocol (TP) for the associated Channel (see below). The DATA portion must be wide enough

to accommodate one full word of the Data Channel contents (data words cannot be spread across multiple segments).

The Segment Interval for each Data Channel represents the minimum spacing between consecutive data samples for that

Channel. (Note - the minimum spacing applies if every allocated segment is populated with new data; in many cases,

additional bandwidth is allocated, as described below, and not every allocated segment is used.)

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 Transport Protocol (TP) defines the flow control or handshaking method used by the Ports associated with a Data

Channel. The applicable flow control mode(s) depend on the relationship between the audio sample rate (flow rate) and the

SLIMbus CLK frequency. If the two rates are synchronised and integer-related, then no flow control is needed; in other

cases, the flow may be regulated by

the use of a ‘Presence’ bit. The Presence bit can either 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 Transport Protocol (TP), Segment Distribution (SD), and the Segment

Length (SL) parameters. Each of these is described above.

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 synchronised 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 Segment Length (SL) and Segment Distribution (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) 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, then Segment Rate must be greater than the Presence Rate,

to ensure 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).

CS47L85 Datasheet(PDF) 192 Page - Cirrus Logic

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