| DIE | Clears stall or remote wake-up and clears power states | |
GET_CONFIGURATION | D | Get current configuration number (or 0 if not configured) |
GET_DESCRIPTOR | D | Get descriptor: Device, String or Configuration, Interface, and Endpoint. |
GET_INTERFACE | I | Get alternate setting for interface |
GET_STATUS | DIE | Get status, e.g., whether device is self-powered andwhether remote wake-up is signalled, or whether end-point is stalled. |
SET_ADDRESS | D | Set the device's address |
SET_CONFIGURATION | D | Set the configuration number |
SET_DESCRIPTOR | D | Set or add a descriptor |
SET_FEATURE | DIE | Sets stall or remote wake-up and sets power states |
SET_INTERFACE | I | Select an alternate interface setting |
SYNCH_FRAME | E | Used in isochronous transfers to indicate the start of a frame pattern. |
For example, the SET_ADDRESS request is sent to assign a USB address to a device. The device returns ACK when complete. A GET_DESCRIPTOR request asks for one of the descriptors. The descriptor is returned in one or more DATA packets.
Each device class usually has various control transfer requests defined. See the appropriate specification for details.
Table 20.5 shows the basic types of descriptor that a device should return, along with a summary of the information in each descriptor. Figure 20.1 gives a view of the relationship between the various descriptors. String descriptors are optional. Further class specific or vendor specific descriptors can be returned. Table 20.6 lists the standard descriptor type constants.
Configuration and endpoint descriptors must not include a descriptor for Endpoint 0.
An interface may have
For isochronous requests, the endpoint maximum packet size reserves bus time.
Table 20.5 USB descriptor types and fields
| Descriptor | Fields |
|---|---|
Device | Vendor ID, Product ID, and Device release number. Device class, sub class, and protocol. Number of configurations |
Configuration | Number of interfaces. Attributes: bus-powered, self-powered, supports remote wake-up. Maximum power required |
Interface | Interface number, class, subclass, and protocol. Number of endpoints. |
Endpoint | Endpoint number, direction, transfer type, maximum packet size, and interrupt polling interval. |
String | String index 0: Language ID supported by device. Others: Unicode string and length |
Table 20.6 Standard descriptor type constants
USB_DEVICE_DESCRIPTOR_TYPE | 0x01 |
