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UDA1335H

Universal Serial Bus (USB) Audio Playback Recording Peripheral (APRP)

Philips Electronics 

Philips Semiconductors

Universal Serial Bus (USB) Audio

Playback Recording Peripheral (APRP)

Preliminary specification

UDA1335H

GENERAL DESCRIPTORS

The UDA1335H supports one configuration containing a

control interface, two audio interfaces and a HID interface.

The descriptor map that describes this configuration is

partly fixed and partly programmable.

The programmable part can be retrieved from one of four

configuration maps located in the firmware or from an

I2C-bus EEPROM. At start-up time one of four internal

configuration maps can be selected depending on the

logical combination of GP3 and GP4. It is possible to

overwrite this configuration map with a configuration map

loaded from an I2C-bus EEPROM.

AUDIO DEVICE CLASS SPECIFIC DESCRIPTORS

The audio device class is partly specified with standard

descriptors and partly with specific audio device class

descriptors. The standard descriptors specify the number

and the type of the interface or endpoint. The UDA1335H

supports 7 different audio modes:

• 8-bit PCM mono or stereo audio data

• 16-bit PCM mono or stereo audio data

• 24-bit PCM mono or stereo audio data

• Zero bandwidth mode.

Each mode is defined as an alternate setting of the audio

interface, selectable with the standard audio streaming

interface descriptor bAlternateSetting field.

The seven alternate settings are described in more detail

by the specific audio device class descriptors.

The UDA1335H supports the input terminal, output

terminal and the feature unit descriptors.

The input and output terminals are not controllable via the

USB. The feature unit provides the basic manipulation of

the incoming logical channels.

The supported sound features are:

• Volume control

• Mute control

• Treble control

• Bass control

• Bass Boost control.

The maximum number of audio data samples within a USB

packet arriving on the isochronous sink endpoint is

restricted by the buffer capacity of this isochronous

endpoint. The maximum buffer capacity is 336 bytes/ms.

The input terminals can be defined by means of

wTerminalType.

THE STANDARD AUDIO STREAMING INTERFACE DESCRIPTOR

FOR THE ISOCHRONOUS DATA SINK ENDPOINT

In this section the descriptors are given for interface 1

which is used for receiving isochronous audio data from

the host.

Although in this specific UDA1335H application no

endpoint control properties can be used on the

isochronous adaptive sink endpoint, the descriptors are

still necessary to inform the host about the definition of this

endpoint: isochronous, adaptive, sink, continuous

sampling frequency (at input side of this endpoint) with a

lower boundary of 5 kHz and an upper boundary of

55 kHz.

The audio class specific descriptors can be requested with

the ‘Get Descriptor: configuration request’, which returns

all the descriptors, except the device descriptor.

For each alternate setting with audio, a maximum

bandwidth is claimed as indicated in the standard

isochronous audio data endpoint descriptor

wMaxPacketSize field. To allow a small overshoot in the

number of audio samples per packet, the top sample

frequency of 55 kHz is taken in the calculation of the

bandwidth for each alternate setting. For each alternate

setting, with its own isochronous audio data endpoint

descriptor, wMaxPacketSize field is then defined as

described in Table 6.

Table 6 Audio bandwidth at each audio mode

ALTERNATE

SETTING

AUDIO MODE

1

8-bit PCM, mono

2

8-bit PCM, stereo

3

16-bit PCM, mono

4

16-bit PCM, stereo

5

24-bit PCM, mono

6

24-bit PCM, stereo

wMaxPacketSize

(HEX)

3 800

7 000

7 000

E000

A800

5 001

THE STANDARD AUDIO STREAMING INTERFACE DESCRIPTOR

FOR THE ISOCHRONOUS DATA SOURCE ENDPOINT

Interface 2 is used for sending isochronous audio data to

the host. It has the same alternate settings as interface 1.

1998 Aug 28

14

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