CS47L35 datasheet(124/300 Pages) CIRRUS

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DS1085F3

CS47L35

4.8 SLIMbus Interface

• A frame consists of 192 slots.

• Eight 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 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 typically comprises control space (for bus messages, synchronization, 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 (see Section 4.8.3); the remainder of the control space are allocated to the

message channel.

4.8.3

Control Space

Framing information is provided in slots 0 and 96 of every frame. Slot 0 contains a 4-bit synchronization code; slot 96

contains the 32-bit framing information, transmitted 4 bits at a time over the eight 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 synchronization. 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 depends 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.

4.8.4

Data Space

The data space can be organized 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, organized 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 reconfigure any data channel.

Each segment may comprise TAG, AUX, and DATA portions. Any of these portions may have a length of zero; the exact

composition depends on the transport protocol (TP) for the associated channel. 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 that the minimum spacing applies if every allocated segment is populated with new data; in many cases,

additional bandwidth is allocated and not every allocated segment is used.)

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