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Register Description and Programming Model
words and longwords. The user must make sure that any word
or longword fields are stored in the correct byte order.
A device may support multiple configurations. Within any one configuration, the device
may support multiple interfaces. An interface consists of a set of endpoints that presents to
the host a single feature or function of the device. An interface within a configuration may
have alternate settings that redefine the characteristics of the associated endpoints. All
devices must provide a device descriptor and at least one configuration, interface and
endpoint descriptor. Each configuration must have at least one interface and one endpoint
descriptor. Only one configuration is effective at any time, but several interfaces and their
related endpoints may be operational at the same time. Only one setting for a particular
interface is effective at any time.
12.3.3.2 USB Device Configuration Example
The example descriptor structure in Figure 12-23 shows a device with three different
configurations. Refer to Chapter 9 of the USB Specification for information on the contents
of each descriptor.
Interface #0
Descriptor
Endpoint #1
Descriptor
Figure 12-23. Example USB Configuration Descriptor Structure
This example is described in the configuration RAM sequence shown below. The device
descriptor begins at address MBAR + 0x1400. Each descriptor must immediately follow
the previous descriptor without any empty locations between them.
1. Device Descriptor
2. Configuration #1 Descriptor
3. Interface #0 Descriptor
4. Endpoint #1 Descriptor
5. Endpoint #2 Descriptor
12-28
Configuration #1
Descriptor
Interface #1
Descriptor
Endpoint #2
Endpoint #3
Descriptor
Descriptor
MCF5272 User's Manual
Device
Descriptor
Configuration #2
Descriptor
Interface #0
Descriptor
Endpoint #1
Descriptor
Configuration #3
Descriptor
Interface #0
Descriptor
Endpoint #1
Endpoint #2
Descriptor
Descriptor
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