Intel IXP400 manual Configuration, Host-Device Request Summary Sheet 2

Intel® IXP400 Software

Access-Layer Components: USB Access (ixUSB) API

Table 60. Host-Device Request Summary (Sheet 2 of 2)

Request			Name
	Sets existing descriptors or adds new descriptors.
SET_DESCRIPTOR	Existing descriptors include: †
	•	Device	• Configuration	• String
	•	Interface	• Endpoint
GET_DESCRIPTOR	Returns the specified descriptor, if it exists.
SET_INTERFACE	Selects an alternate setting for the UDC’s interface.
GET_INTERFACE	Returns the selected alternate setting for the specified interface.
	Returns the UDC’s status including:
GET_STATUS	•	Remote wake-up	• Self-powered	• Data direction
	•	Endpoint number	• Stall status
SET_ADDRESS	Sets the UDC’s 7-bit address value for all future device accesses.
SYNCH_FRAME	Sets an endpoint’s synchronization frame.

†Interface and endpoint descriptors cannot be retrieved or set individually. They exist only embedded within configuration descriptors.

Via control endpoint 0, the user must decode and respond to the GET_DESCRIPTOR command.

Refer to the Universal Serial Bus Specification Revision 1.1 for a full description of host-device requests.

22.4.1.1Configuration

In response to the GET_DESCRIPTOR command, the user sends back a description of the UDC configuration. The UDC can physically support more data-channel bandwidth than the USB will allow. When responding to the host, the user must be careful to specify a legal USB configuration.

For example, if the user specifies a configuration of six isochronous endpoints of 256 bytes each, the host will not be able to schedule the proper bandwidth and will not take the UDC out of Configuration 0. The user must determine which endpoints to not tell the host about, so that they will not get used.

Another option, especially attractive for isochronous endpoints, is to describe a configuration of less than 256 bytes maximum packet to the host. The direction of the endpoints is fixed and the UDC will physically support only the following maximum packet sizes:

•Interrupt endpoints — 8 bytes

•Bulk endpoints — 64 bytes

•Isochronous endpoints — 256 bytes

In order to increase flexibility, the UDC supports a total of four configurations. While each of these configurations is identical within the UDC, the software can be used to make three distinct configurations. Configuration 0 is a default configuration of endpoint 0 only.

For a detailed description of the configuration descriptor, see the USB 1.1 specification.

April 2005	IXP400 Software Version 2.0	Programmer’s Guide
304	Document Number: 252539, Revision: 007