AN249 데이터 시트보기 (PDF) - Silicon Laboratories

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AN249

HUMAN INTERFACE DEVICE TUTORIAL

Silicon Laboratories 

AN249

4.1.2. Descriptor Definition Example

The definition might look like the following:

const code device_descriptor DeviceDesc =

{

18,

// bLength

0x01,

// bDescriptorType

0x1001,

// bcdUSB

0x00,

// bDeviceClass

0x00,

// bDeviceSubClass

0x00,

// bDeviceProtocol

EP0_PACKET_SIZE,

// bMaxPacketSize0

0xC410,

// idVendor

0x0001,

// idProduct

0x0000,

// bcdDevice

0x01,

// iManufacturer

0x02,

// iProduct

0x00,

// iSerialNumber

0x01

// bNumConfigurations

}; //end of DeviceDesc

The definition exactly follows the declaration for the struct device_descriptor. All contents in this definition

must be valid at the firmware system’s compile time because all of these values will be stored in nonvolatile

memory. Descriptor values stored in multiple bytes must follow the "little endian" style of formatting, where the least

significant byte is stored first. For example, a value of 300 or 0x012C, would be stored as 0x2C01.

4.1.3. A Reminder About Descriptors

Many HID devices have very similar descriptor contents, and in many cases, the descriptors defined in the

firmware template will need to be changed in only a few places to create a customized HID-class device that suits

the needs of a given application. For detailed discussions on each descriptor’s contents, read the sections of this

document describing the firmware template and the two examples created by modifying the template.

4.2. Device Responsibilities During Enumeration

A device’s main responsibility during enumeration is to respond to requests for information made by the host

system in a timely and accurate manner. The device transfers all enumeration data across the control endpoint. In

the firmware template, this endpoint is handled during execution of the USB ISR.

6

Rev. 0.2

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