C371346_375F2440A66FD1C882296D07948AE54C.pdf - 第17页

CM108AH

Highly Integrated USB Audio I/O Controller

www.cmedia.com.tw

7.3 HID Feature

The CM108AH’s HID feature allows users to set volume up, volume down, playback mute and recording mute

button pins, and reports the changes to the host to synchronize host side settings. In addition, all CM108AH

internal registers can be accessed via HID function call.

7.3.1 What’s HID?

USB protocols can configure devices at startup or when they are plugged in at run time. These devices are

categorized into various device classes. Each device class defines the common behavior and protocols for

devices that serve similar functions. The HID (Human Interface Device) class is one of the device classes.

The HID class consists primarily of devices that are used to control the operation of computer systems.

Typical examples of HID class devices include:

 Keyboards and pointing devices: mice, trackballs and joysticks

 Front-panel controls: knobs, switches, buttons and sliders

 Controls that might be found on VCR remote controls, games or simulation devices: data gloves,

throttles, and steering wheels

 Devices that may not require human interaction but provide data in a similar format to HID class

devices: bar-code readers, thermometers or voltmeters

CM108AH

Highly Integrated USB Audio I/O Controller

www.cmedia.com.tw

7.3.2 HID Descriptors

HID Interface Descriptor

Offset

Field

Size

Value (Hex)

Description

0

bLength

1

09

Size of this descriptor: 9 bytes

1

bDescriptorType

1

04

Interface descriptor type

2

bInterfaceNumber

1

03

Interface number: 3

3

bAlternateSetting

1

00

Alternate: 0

4

bNumEndpoints

1

01

Number of endpoints used by this interface: 1

5

bInterfaceClass

1

03

Interface class: HID

6

bInterfaceSubClass

1

00

Subclass: no

7

bInterfaceProtocol

1

00

Must be set to 0

8

iInterface

1

00

String descriptor index that describes this interface

HID Descriptor

Offset

Field

Size

Value (Hex)

Description

0

bLength

1

09

Total: 9 bytes

1

bDescriptorType

1

21

HID descriptor type

2

bcdHID

2

0100

HID class version 1.0

4

bCountryCode

1

00

5

bNumDescriptors

1

01

6

bDescriptorType

1

22

Report descriptor

7

wDescriptorLength

2

0030

Total size of the optional descriptor: 48 bytes

Interrupt IN Endpoint Descriptor

Offset

Field

Size

Value (Hex)

Description

0

bLength

1

07

Total: 7 bytes

1

bDescriptorType

1

05

Endpoint descriptor type

2

bEndpointAddress

1

83

In Endpoint Number = 3

3

bmAttributes

1

03

Interrupt endpoint type

4

wMaxPacketSize

2

0004

Maximum packet size: 4 bytes

6

bInterval

1

2

2ms

CM108AH

Highly Integrated USB Audio I/O Controller

www.cmedia.com.tw

7.3.3 Windows Software Architecture for HID

Note: Please contact our sales for a C-Media SDK sample if needed

PCI enumerator

USB class driver (USBD.SYS)

USB hub driver (USBHUB.SYS)

USB

MiniDriver( HIDUSB.SYS)

HID class driver(HIDCLASS.SYS)

Gameport

MiniDriver(HIDGAME.SYS)

Gameport

Enumerator(GAMEUM.SYS)

Audio Driver

Keyboard-class driver

Mouse-class driver

Joy stick-class driver

C-Media SDK

Reports

(Device specification)

Winmm.dll

Direct input

HID.dll

Applications

User32.exe or User.exe