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AT85C51SND3Bx

7632A–MP3–03/06

Figure 71. Audio Processor Block Diagram

Audio Buffer The audio buffer receives the audio data flow coming from DFC or the C51. It is based

on 1 Kbyte of dual-port RAM.

Buffer Description The audio buffer can be accessed in read or write mode by both C51 and DFC. Access

selection is done by the ABACC bit in APCON1. Considering the DFC, two channels

can be established at the same time one in which the audio processor is the source and

one in which the audio processor is the destination. To achieve such scheme, the audio

buffer can be configured using ABSPLIT in APCON1 as one (see

Figure 72a) or two

(see Figure 72b) buffers, each containing two data packets of 512 or 256 bytes size.

Figure 72. Audio Buffer Configuration

Internal read or write pointers can be reset at any time by setting respectively ABRPR

and ABWPR bits in APCON1. These bits are automatically reset by hardware.

Buffer Management The C51 reads from or writes to the buffer through the APDAT register. Management is

controlled by a couple of flags informing the user that data can be written to the buffer or

read from the buffer depending on the current operation.

In case of write (audio stream decoding or codec firmware update) APREQI flag in

APINT is set every time a data packet (256 or 512 bytes) can be written to the buffer i.e.

buffer empty or half full. APREQI is cleared when the buffer becomes full.

In case of read (audio stream encoding) APRDYI flag in APINT is set every time a data

packet (256 or 512 bytes) can be retrieved from the buffer i.e. buffer full or half full.

APRDYI is cleared when the buffer becomes empty.

These flags can generate an interrupt when APREQE bit and APRDYE bit in APIEN are

respectively set (see

Section “Interrupts”).

Audio Buffer

Digital Audio

Processor

CPU

CPU/DFC

Audio DAC

Interface

Audio Codec

Baseband

Processor

CPU (APDAT)

DFC

512-byte512-byte

CPU (APDAT)

DFC

256-byte

rd pointer

wr pointer

rd pointer

256-byte

256-byte 256-byte

a. Single Buffer (ABSPLIT= 0)

b. Double Buffer (ABSPLIT= 1)

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