CP3SP33SMSSLASHNOPB datasheet(254/407 Pages) TI1

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APB Bus

Filter

Engine

1-Bit 64 kHz

16-Bit

64 kHz

16-Bit x 8-Word

CVSD Out FIFO

16-Bit 8 kHz

CVSD

Encoder

DMA

Interrupt

2 MHz

Clock Input

CVSD

Decoder

u/A-Law

16-Bit 8 kHz

u/A-Law

DS446

1-Bit 64 kHz

16-Bit x 8-Word

CVSD In FIFO

CP3SP33

SNOSCW5 – MAY 2013

www.ti.com

•

Fixed-rate mode—125 µs (8 kHz) per PCM sample, based on a 2 MHz module clock frequency.

Intended for exchanging data with an external codec.

•

Free-running mode—runs at any module clock frequency up to the PCLK Clock frequency. CVSD

transcoder activity is governed by DMA acknowledgment on CVSDIN and CVSDOUT channels.

Intended for exchanging PCM data over a Bluetooth channel.

On the CVSD side, read and write FIFOs buffer up to 8 words of data. On the PCM side, double-buffered

registers are provided. The intended use is to move CVSD data with an interrupt handler, and to move

PCM data with DMA. Figure 26-1 is a block diagram of a CVSD/PCM converter module.

Figure 26-1. CVSD/PCM Converter Block Diagram

26.1 Operation

In fixed-rate mode, the module converts between PCM data and CVSD data at a fixed PCM data rate of 8

kHz. Due to compression, the data rate on the CVSD side is only 4 kHz.

If PCM interrupts are enabled, every 125 µs (8 kHz) an interrupt will occur and the interrupt handler can

operate on some or all of the four audio streams: CVSD in, CVSD out, PCM in, and PCM out.

Alternatively, a DMA request is issued every 125 µs and the DMA controller is used to move the PCM

data between the CVSD/PCM module and the audio interface.

If CVSD interrupts are enabled, an interrupt is issued when either one of the CVSD FIFOs is almost empty

or almost full. On the PCM data side there is double buffering, and on the CVSD side there is an eight

word (8-bit × 16-bit) FIFO for the read and write paths.

Inside the module, a filter engine receives the 8-kHz stream of 16-bit samples and interpolates to generate

a 64-kHz stream of 16-bit samples. This goes into a CVSD encoder which converts the data into a single-

bit delta stream using the CVSD parameters as defined by the Bluetooth specification. There is a similar

path that reverses this process, converting the CVSD 64-kHz bit stream into a 64-kHz 16-bit data stream.

The filter engine then decimates this stream into an 8-kHz, 16-bit data stream.

254

Dual CVSD/PCM Conversion Modules

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