Cypress Semiconductor FX2LP Información técnica Pagina 73

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Chapter 2. Endpoint Zero Page 2-19
Configurations, Interfaces, and Alternate Settings
A USB device has one or more configu-
rations. Only one configuration is active
at any time.
A configuration has one or more inter-
faces, all of which are concurrently
active. Multiple interfaces allow different
host-side device drivers to be associated
with different portions of a USB device.
Each interface has one or more alternate
settings. Each alternate setting has a
collection of one or more endpoints.
This structure is a software model; the FX2 takes no action when these settings change.
However, the firmware must re-initialize endpoints when the host changes configurations
or interfaces alternate settings.
As far as the firmware is concerned, a configuration is simply a byte variable that indicates
the current setting.
The host issues a
Set Configuration
request to select a configuration, and a
Get Configura-
tion
request to determine the current configuration.
Device
Config 2
Low Power
Config 1
High Power
Interface 1
audio
Interface 0
CDROM
control
Alt Setting
0
Alt Setting
1
Alt Setting
3
Interface 2
video
Interface 3
data
storage
Concurrent
One at a time
ep
ep
ep
One at a time
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