Architecture

STM7710

18/23

2.14

Audio subsystem

The audio subsystem comprises the audio controller, the MMDSP 24-bit audio digital signal

processor and the audio output interfaces. The audio subsystem is shown in Figure 8.

Figure 8.

Audio decoder interface block diagram

2.14.1

Audio decoder interface

The audio decoder interface receives, buffers and reformats audio data. It handles up to

three audio data flows concurrently.

●

It receives a raw PCM stream from an external source through the PCM input interface

or receives a compressed data stream from an internal source such as the PTI and

stores this in a memory buffer through DMA. This is used to buffer and play the main

audio for the digital or analog program.

●

It receives a PCM file or stream from a memory buffer through DMA and delivers this to

the MMDSP’s 2nd input for sample rate conversion and mixing with the main audio.

The second input may also receive a PCM stream directly from the PCM input

interface. This is used to play PCM data which is mixed with the main audio.

PCM buffer

Channel 1 bit buffer

I2S

Off-chip DDR SDRAM

Audio FIFO in

CDin

main

Audio FIFO out

PCM FIFO out

Register

interface

Audio decoder

Audio decoder interface

In 1

audio

Decoding/

PCM bypass

2 channels

Mixer

Compressed

audio

MUX

Sample rate

conversion

IEC958/1937

formatting

S/PDIF

interface

Stereo audio

DAC system

Register

interface

Main

2nd

input

MMDSP

from PTI

out