CS5530 datasheet(117/241 Pages) NSC

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Functional Description (Continued)

3.7.1.4

Programming Model

The following discussion explains, in steps, how to initiate

and maintain a bus master transfer between memory and

an audio slave device.

In the steps listed below, the reference to “Example”

refers to Figure 3-20, PRD Table Example.

Software creates a PRD table in system memory.

Each PRD entry is 8 bytes long; consisting of a base

address pointer and buffer size. The maximum data

that can be transferred from a PRD entry is 64 KB. A

PRD table must be aligned on a 4-byte boundary.

Thelast PRD inaPRD tablemust havethe EOTor

JMP bit set.

Example - Assume the data is outbound. There are

three PRDs in the example PRD table. The first two

PRDs (PRD_1, PRD_2) have only the EOP bit set.

The last PRD (PRD_3) has only the JMP bit set. This

example creates a PRD loop.

Software loads the starting address of the PRD table

by programming the PRD Table Address Register.

Example - Program the PRD Table Address Register

with Address_3.

Software must fill the buffers pointed to by the PRDs

with audio data. It is not absolutely necessary to fill

the buffers; however, the buffer filling process must

stay ahead of the buffer emptying. The simplest way

to do this is by using the EOP flags to generate an

SMI when a PRD is empty.

Example - Fill Audio Buffer_1 and Audio Buffer_2.

The SMI generated by the EOP from the first PRD

allows the software to refill Audio Buffer_1. The

second SMI will refill Audio Buffer_2. The third SMI

will refill Audio Buffer_1 and so on.

Read the SMI Status Register to clear the Bus

Master Error and End of Page bits (bits 1 and 0).

Set the correct direction to the Read or Write Control

bit (Command Register bit 3). Note that the direction

of the data transfer of a particular bus master is fixed

and therefore the direction bit must be programmed

accordingly. It is assumed that the codec has been

properly programmed to receive the audio data.

Engage the bus master by writing a “1” to the Bus

Master Control bit (Command Register bit 0).

The bus master reads the PRD entry pointed to by

the PRD Table Address Register and increments the

address by 08h to point to the next PRD. The transfer

begins.

Example -

The

bus

master

now

properly

programmed to transfer Audio Buffer_1 to a specific

slot(s) in the AC97 interface.

Figure 3-20. PRD Table Example

Address_1

Size_1

EOT = 0

Audio

Buffer_1

Audio

Buffer_2

Size_1

Size_2

Address_1

EOP = 1

JMP = 0

Address_2

Size_2

EOT = 0

EOP = 1

JMP = 0

Address_3

Don’t Care

EOT = 0

EOP = 0

JMP = 1

PRD_1

PRD_2

PRD_3

Address_2

Address_3

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