Spinpoint M8U-Internal Product Manual REV 3.4
63
INSTALLATION
the effect of resetting the device. A reset USB device has the following characteristics:
Responds to the default USB address
Is not configured
Is not initially suspended
When a device is removed from a hub port, the hub disables the port where the device was attached and
notifies the host of the removal.
6.3.6.2.2
Address Assignment
When a USB device is attached, the host is responsible for assigning a unique address to the device. This is
done after the device has been reset by the host, and the hub port where the device is attached has been
enabled.
6.3.6.2.3
Configuration
A USB device must be configured before its function(s) may be used. The host is responsible for configuring
a USB device. The host typically requests configuration information from the USB device to determine the
device’s capabilities.
As part of the configuration process, the host sets the device configuration and, where necessary, selects the
appropriate alternate settings for the interfaces. Within a single configuration, a device may support multiple
interfaces. An interface is a related set of endpoints that present a single feature or function of the device to
the host. The protocol used to communicate with this related set of endpoints and the purpose of each
endpoint within the interface may be specified as part of a device class or vendor-specific definition.
In addition, an interface within a configuration may have alternate settings that redefine the number or
characteristics of the associated endpoints. If this is the case, the device must support the GetInterface ()
request to report the current alternate setting for the specified interface and SetInterface () request to select the
alternate setting for the specified interface.
Within each configuration, each interface descriptor contains fields that identify the interface number and the
alternate setting. Interfaces are numbered from zero to one less than the number of concurrent interfaces
supported by the configuration. Alternate settings range from zero to one less than the number of alternate
settings for a specific interface. The default setting when a device is initially configured is alternate setting
zero.
In support of adaptive device drivers that are capable of managing a related group of USB devices, the device
and interface descriptors contain
Class
,
SubClass
, and
Protocol
fields. These fields are used to identify the
function(s) provided by a USB device and the protocols used to communicate with the function(s) on the
device. A class code is assigned to a group of related devices that has been characterized as a part of a USB
Class Specification. A class of devices may be further subdivided into subclasses, and, within a class or
subclass, a protocol code may define how the Host Software communicates with the device.
Note: The assignment of class, subclass, and protocol codes must be coordinated but is beyond the scope of
this specification.
6.3.6.2.4
Data Transfer
Data may be transferred between a USB device endpoint and the host in one of four ways. An endpoint
number may be used for different types of data transfers in different alternate settings. However, once an
alternate setting is selected (including the default setting of an interface), a USB device endpoint uses only
one data transfer method until a different alternate setting is selected.
6.3.6.2.5
Power Management
■
Power Budgeting
USB bus power is a limited resource. During device enumeration, a host evaluates a device’s power
requirements. If the power requirements of a particular configuration exceed the power available to the
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