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IXP400 Software
Access-Layer Components: USB Access (ixUSB) API
April 2005 IXP400 Software Version 2.0 Programmer’s Guide
304 Document Number: 252539, Revision: 007
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.
22.4.1.1 Configuration
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.
SET_DESCRIPTOR
Sets existing descriptors or adds new descriptors.
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.
GET_STATUS
Returns the UDC’s status including:
• 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.
Table 60. Host-Device Request Summary (Sheet 2 of 2)
Request Name
† Interface and endpoint descriptors cannot be retrieved or set individually. They exist only embedded within
configuration descriptors.